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Types
Dyssomnias – A broad category of sleep disorders characterized by either hypersomnia or insomnia. The three major subcategories include intrinsic (i.e., arising from within the body), extrinsic (secondary to environmental conditions or various pathologic conditions), and disturbances of circadian rhythm.
Insomnia: Insomnia may be primary or it may be comorbid with or secondary to another disorder such as a mood disorder (i.e., emotional stress, anxiety, depression) or underlying health condition (i.e., asthma, diabetes, heart disease, pregnancy or neurological conditions).
Primary hypersomnia: Hypersomnia of central or brain origin
Narcolepsy: A chronic neurological disorder (or dyssomnia), which is caused by the brain's inability to control sleep and wakefulness.
Idiopathic hypersomnia: A chronic neurological disease similar to narcolepsy, in which there is an increased amount of fatigue and sleep during the day. Patients who have idiopathic hypersomnia cannot obtain a healthy amount of sleep for a regular day of activities. This hinders the patients' ability to perform well, and patients have to deal with this for the rest of their lives.
Recurrent hypersomnia, including Kleine–Levin syndrome
Post traumatic hypersomnia
Menstrual-related hypersomnia
Sleep disordered breathing (SDB), including (non-exhaustive):
Several types of sleep apnea
Snoring
Upper airway resistance syndrome
Restless leg syndrome
Periodic limb movement disorder
Circadian rhythm sleep disorders
Delayed sleep phase disorder
Advanced sleep phase disorder
Non-24-hour sleep–wake disorder
Parasomnias – A category of sleep disorders that involve abnormal and unnatural movements, behaviors, emotions, perceptions, and dreams in connection with sleep.
Bedwetting or sleep enuresis
Bruxism (Tooth-grinding)
Catathrenia – nocturnal groaning
Exploding head syndrome – Waking up in the night hearing loud noises.
Sleep terror (or Pavor nocturnus) – Characterized by a sudden arousal from deep sleep with a scream or cry, accompanied by some behavioral manifestations of intense fear.
REM sleep behavior disorder
Sleepwalking (or somnambulism)
Sleep talking (or somniloquy)
Sleep sex (or sexsomnia)
Medical or psychiatric conditions that may produce sleep disorders
22q11.2 deletion syndrome
Alcoholism
Mood disorders
Depression
Anxiety disorder
Nightmare disorder
Panic | Sleep disorder | Wikipedia | 511 | 46966 | https://en.wikipedia.org/wiki/Sleep%20disorder | Biology and health sciences | Mental disorders | Health |
Dissociative identity disorder
Psychosis (such as Schizophrenia)
Sleeping sickness – a parasitic disease which can be transmitted by the Tsetse fly.
Jet lag disorder – Jet lag disorder is a type of circadian rhythm sleep disorder that results from rapid travel across multiple time zones. Individuals experiencing jet lag may encounter symptoms such as excessive sleepiness, fatigue, insomnia, irritability, and gastrointestinal disturbances upon reaching their destination. These symptoms arise due to the mismatch between the body's circadian rhythm, synchronized with the departure location, and the new sleep/wake cycle needed at the destination. | Sleep disorder | Wikipedia | 129 | 46966 | https://en.wikipedia.org/wiki/Sleep%20disorder | Biology and health sciences | Mental disorders | Health |
Pollen is a powdery substance produced by most types of flowers of seed plants for the purpose of sexual reproduction. It consists of pollen grains (highly reduced microgametophytes), which produce male gametes (sperm cells).
Pollen grains have a hard coat made of sporopollenin that protects the gametophytes during the process of their movement from the stamens to the pistil of flowering plants, or from the male cone to the female cone of gymnosperms. If pollen lands on a compatible pistil or female cone, it germinates, producing a pollen tube that transfers the sperm to the ovule containing the female gametophyte. Individual pollen grains are small enough to require magnification to see detail. The study of pollen is called palynology and is highly useful in paleoecology, paleontology, archaeology, and forensics.
Pollen in plants is used for transferring haploid male genetic material from the anther of a single flower to the stigma of another in cross-pollination. In a case of self-pollination, this process takes place from the anther of a flower to the stigma of the same flower.
Pollen is infrequently used as food and food supplement. Because of agricultural practices, it is often contaminated by agricultural pesticides.
Structure and formation
Pollen itself is not the male gamete. It is a gametophyte, something that could be considered an entire organism, which then produces the male gamete. Each pollen grain contains vegetative (non-reproductive) cells (only a single cell in most flowering plants but several in other seed plants) and a generative (reproductive) cell. In flowering plants the vegetative tube cell produces the pollen tube, and the generative cell divides to form the two sperm nuclei.
Pollen grains come in a wide variety of shapes, sizes, and surface markings characteristic of the species (see electron micrograph, right). Pollen grains of pines, firs, and spruces are winged. The smallest pollen grain, that of the forget-me-not (Myosotis spp.), is 2.5–5 μm (0.005 mm) in diameter. Corn pollen grains are large, about 90–100 μm. Most grass pollen is around 20–25 μm. Some pollen grains are based on geodesic polyhedra like a soccer ball. | Pollen | Wikipedia | 496 | 46980 | https://en.wikipedia.org/wiki/Pollen | Biology and health sciences | Plant reproduction | null |
Formation
Pollen is produced in the microsporangia in the male cone of a conifer or other gymnosperm or in the anthers of an angiosperm flower.
In angiosperms, during flower development the anther is composed of a mass of cells that appear undifferentiated, except for a partially differentiated dermis. As the flower develops, fertile sporogenous cells, the archespore, form within the anther. The sporogenous cells are surrounded by layers of sterile cells that grow into the wall of the pollen sac. Some of the cells grow into nutritive cells that supply nutrition for the microspores that form by meiotic division from the sporogenous cells. The archespore cells divide by mitosis and differentiate to form pollen mother cells (microsporocyte, meiocyte).
In a process called microsporogenesis, four haploid microspores are produced from each diploid pollen mother cell, after meiotic division. After the formation of the four microspores, which are contained by callose walls, the development of the pollen grain walls begins. The callose wall is broken down by an enzyme called callase and the freed pollen grains grow in size and develop their characteristic shape and form a resistant outer wall called the exine and an inner wall called the intine. The exine is what is preserved in the fossil record.
Two basic types of microsporogenesis are recognised, simultaneous and successive. In simultaneous microsporogenesis meiotic steps I and II are completed before cytokinesis, whereas in successive microsporogenesis cytokinesis follows. While there may be a continuum with intermediate forms, the type of microsporogenesis has systematic significance. The predominant form amongst the monocots is successive, but there are important exceptions.
During microgametogenesis, the unicellular microspores undergo mitosis and develop into mature microgametophytes containing the gametes. In some flowering plants, germination of the pollen grain may begin even before it leaves the microsporangium, with the generative cell forming the two sperm cells.
Structure | Pollen | Wikipedia | 445 | 46980 | https://en.wikipedia.org/wiki/Pollen | Biology and health sciences | Plant reproduction | null |
Except in the case of some submerged aquatic plants, the mature pollen grain has a double wall. The vegetative and generative cells are surrounded by a thin delicate wall of unaltered cellulose called the endospore or intine, and a tough resistant outer cuticularized wall composed largely of sporopollenin called the exospore or exine. The exine often bears spines or warts, or is variously sculptured, and the character of the markings is often of value for identifying genus, species, or even cultivar or individual.
The spines may be less than a micron in length (spinulus, plural spinuli) referred to as spinulose (scabrate), or longer than a micron (echina, echinae) referred to as echinate. Various terms also describe the sculpturing such as reticulate, a net like appearance consisting of elements (murus, muri) separated from each other by a lumen (plural lumina). These reticulations may also be referred to as brochi.
The pollen wall protects the sperm while the pollen grain is moving from the anther to the stigma; it protects the vital genetic material from drying out and solar radiation. The pollen grain surface is covered with waxes and proteins, which are held in place by structures called sculpture elements on the surface of the grain. The outer pollen wall, which prevents the pollen grain from shrinking and crushing the genetic material during desiccation, is composed of two layers. These two layers are the tectum and the foot layer, which is just above the intine. The tectum and foot layer are separated by a region called the columella, which is composed of strengthening rods. The outer wall is constructed with a resistant biopolymer called sporopollenin. | Pollen | Wikipedia | 378 | 46980 | https://en.wikipedia.org/wiki/Pollen | Biology and health sciences | Plant reproduction | null |
Pollen apertures are regions of the pollen wall that may involve exine thinning or a significant reduction in exine thickness. They allow shrinking and swelling of the grain caused by changes in moisture content. The process of shrinking the grain is called harmomegathy. Elongated apertures or furrows in the pollen grain are called colpi (singular: colpus) or sulci (singular: sulcus). Apertures that are more circular are called pores. Colpi, sulci and pores are major features in the identification of classes of pollen. Pollen may be referred to as inaperturate (apertures absent) or aperturate (apertures present).
The aperture may have a lid (operculum), hence is described as operculate. However the term inaperturate covers a wide range of morphological types, such as functionally inaperturate (cryptoaperturate) and omniaperturate. Inaperaturate pollen grains often have thin walls, which facilitates pollen tube germination at any position. Terms such as uniaperturate and triaperturate refer to the number of apertures present (one and three respectively). Spiraperturate refers to one or more apertures being spirally shaped.
The orientation of furrows (relative to the original tetrad of microspores) classifies the pollen as sulcate or colpate. Sulcate pollen has a furrow across the middle of what was the outer face when the pollen grain was in its tetrad. If the pollen has only a single sulcus, it is described as monosulcate, has two sulci, as bisulcate, or more, as polysulcate. Colpate pollen has furrows other than across the middle of the outer faces, and similarly may be described as polycolpate if more than two. Syncolpate pollen grains have two or more colpi that are fused at the ends. Eudicots have pollen with three colpi (tricolpate) or with shapes that are evolutionarily derived from tricolpate pollen. The evolutionary trend in plants has been from monosulcate to polycolpate or polyporate pollen. | Pollen | Wikipedia | 460 | 46980 | https://en.wikipedia.org/wiki/Pollen | Biology and health sciences | Plant reproduction | null |
Additionally, gymnosperm pollen grains often have air bladders, or vesicles, called sacci. The sacci are not actually balloons, but are sponge-like, and increase the buoyancy of the pollen grain and help keep it aloft in the wind, as most gymnosperms are anemophilous. Pollen can be monosaccate, (containing one saccus) or bisaccate (containing two sacci). Modern pine, spruce, and yellowwood trees all produce saccate pollen.
Pollination
The transfer of pollen grains to the female reproductive structure (pistil in angiosperms) is called pollination. Pollen transfer is frequently portrayed as a sequential process that begins with placement on the vector, moves through travel, and ends with deposition. This transfer can be mediated by the wind, in which case the plant is described as anemophilous (literally wind-loving). Anemophilous plants typically produce great quantities of very lightweight pollen grains, sometimes with air-sacs.
Non-flowering seed plants (e.g., pine trees) are characteristically anemophilous. Anemophilous flowering plants generally have inconspicuous flowers. Entomophilous (literally insect-loving) plants produce pollen that is relatively heavy, sticky and protein-rich, for dispersal by insect pollinators attracted to their flowers. Many insects and some mites are specialized to feed on pollen, and are called palynivores.
In non-flowering seed plants, pollen germinates in the pollen chamber, located beneath the micropyle, underneath the integuments of the ovule. A pollen tube is produced, which grows into the nucellus to provide nutrients for the developing sperm cells. Sperm cells of Pinophyta and Gnetophyta are without flagella, and are carried by the pollen tube, while those of Cycadophyta and Ginkgophyta have many flagella. | Pollen | Wikipedia | 413 | 46980 | https://en.wikipedia.org/wiki/Pollen | Biology and health sciences | Plant reproduction | null |
When placed on the stigma of a flowering plant, under favorable circumstances, a pollen grain puts forth a pollen tube, which grows down the tissue of the style to the ovary, and makes its way along the placenta, guided by projections or hairs, to the micropyle of an ovule. The nucleus of the tube cell has meanwhile passed into the tube, as does also the generative nucleus, which divides (if it has not already) to form two sperm cells. The sperm cells are carried to their destination in the tip of the pollen tube. Double-strand breaks in DNA that arise during pollen tube growth appear to be efficiently repaired in the generative cell that carries the male genomic information to be passed on to the next plant generation. However, the vegetative cell that is responsible for tube elongation appears to lack this DNA repair capability.
In the fossil record
The sporopollenin outer sheath of pollen grains affords them some resistance to the rigours of the fossilisation process that destroy weaker objects; it is also produced in huge quantities. There is an extensive fossil record of pollen grains, often disassociated from their parent plant. The discipline of palynology is devoted to the study of pollen, which can be used both for biostratigraphy and to gain information about the abundance and variety of plants alive — which can itself yield important information about paleoclimates. Also, pollen analysis has been widely used for reconstructing past changes in vegetation and their associated drivers.
Pollen is first found in the fossil record in the late Devonian period, but at that time it is indistinguishable from spores. It increases in abundance until the present day.
Allergy to pollen
Nasal allergy to pollen is called pollinosis, and allergy specifically to grass pollen is called hay fever. Generally, pollens that cause allergies are those of anemophilous plants (pollen is dispersed by air currents.) Such plants produce large quantities of lightweight pollen (because wind dispersal is random and the likelihood of one pollen grain landing on another flower is small), which can be carried for great distances and are easily inhaled, bringing it into contact with the sensitive nasal passages. | Pollen | Wikipedia | 453 | 46980 | https://en.wikipedia.org/wiki/Pollen | Biology and health sciences | Plant reproduction | null |
Pollen allergies are common in polar and temperate climate zones, where production of pollen is seasonal. In the tropics pollen production varies less by the season, and allergic reactions less.
In northern Europe, common pollens for allergies are those of birch and alder, and in late summer wormwood and different forms of hay. Grass pollen is also associated with asthma exacerbations in some people, a phenomenon termed thunderstorm asthma.
In the US, people often mistakenly blame the conspicuous goldenrod flower for allergies. Since this plant is entomophilous (its pollen is dispersed by animals), its heavy, sticky pollen does not become independently airborne. Most late summer and fall pollen allergies are probably caused by ragweed, a widespread anemophilous plant.
Arizona was once regarded as a haven for people with pollen allergies, although several ragweed species grow in the desert. However, as suburbs grew and people began establishing irrigated lawns and gardens, more irritating species of ragweed gained a foothold and Arizona lost its claim of freedom from hay fever.
Anemophilous spring blooming plants such as oak, birch, hickory, pecan, and early summer grasses may also induce pollen allergies. Most cultivated plants with showy flowers are entomophilous and do not cause pollen allergies.
Symptoms of pollen allergy include sneezing, itchy, or runny nose, nasal congestion, red, itchy, and watery eyes. Substances, including pollen, that cause allergies can trigger asthma. A study found a 54% increased chance of asthma attacks when exposed to pollen.
The number of people in the United States affected by hay fever is between 20 and 40 million, including around 6.1 million children and such allergy has proven to be the most frequent allergic response in the nation. Hay fever affects about 20% of Canadians and the prevalence is increasing. There are certain evidential suggestions pointing out hay fever and similar allergies to be of hereditary origin. Individuals who suffer from eczema or are asthmatic tend to be more susceptible to developing long-term hay fever.
Since 1990, pollen seasons have gotten longer and more pollen-filled, and climate change is responsible, according to a new study. The researchers attributed roughly half of the lengthening pollen seasons and 8% of the trend in pollen concentrations to climate changes driven by human activity. | Pollen | Wikipedia | 496 | 46980 | https://en.wikipedia.org/wiki/Pollen | Biology and health sciences | Plant reproduction | null |
In Denmark, decades of rising temperatures cause pollen to appear earlier and in greater amounts, exacerbated by the introduction of new species such as ragweed.
The most efficient way to handle a pollen allergy is by preventing contact with the material. Individuals carrying the ailment may at first believe that they have a simple summer cold, but hay fever becomes more evident when the apparent cold does not disappear. The confirmation of hay fever can be obtained after examination by a general physician.
Treatment
Antihistamines are effective at treating mild cases of pollinosis; this type of non-prescribed drugs includes loratadine, cetirizine and chlorpheniramine. They do not prevent the discharge of histamine, but it has been proven that they do prevent a part of the chain reaction activated by this biogenic amine, which considerably lowers hay fever symptoms.
Decongestants can be administered in different ways such as tablets and nasal sprays.
Allergy immunotherapy (AIT) treatment involves administering doses of allergens to accustom the body to pollen, thereby inducing specific long-term tolerance. Allergy immunotherapy can be administered orally (as sublingual tablets or sublingual drops), or by injections under the skin (subcutaneous). Discovered by Leonard Noon and John Freeman in 1911, allergy immunotherapy represents the only causative treatment for respiratory allergies. | Pollen | Wikipedia | 300 | 46980 | https://en.wikipedia.org/wiki/Pollen | Biology and health sciences | Plant reproduction | null |
Nutrition
Most major classes of predatory and parasitic arthropods contain species that eat pollen, despite the common perception that bees are the primary pollen-consuming arthropod group. Many Hymenoptera other than bees consume pollen as adults, though only a small number feed on pollen as larvae (including some ant larvae). Spiders are normally considered carnivores but pollen is an important source of food for several species, particularly for spiderlings, which catch pollen on their webs. It is not clear how spiderlings manage to eat pollen however, since their mouths are not large enough to consume pollen grains. Some predatory mites also feed on pollen, with some species being able to subsist solely on pollen, such as Euseius tularensis, which feeds on the pollen of dozens of plant species. Members of some beetle families such as Mordellidae and Melyridae feed almost exclusively on pollen as adults, while various lineages within larger families such as Curculionidae, Chrysomelidae, Cerambycidae, and Scarabaeidae are pollen specialists even though most members of their families are not (e.g., only 36 of 40,000 species of ground beetles, which are typically predatory, have been shown to eat pollen—but this is thought to be a severe underestimate as the feeding habits are only known for 1,000 species). Similarly, Ladybird beetles mainly eat insects, but many species also eat pollen, as either part or all of their diet. Hemiptera are mostly herbivores or omnivores but pollen feeding is known (and has only been well studied in the Anthocoridae). Many adult flies, especially Syrphidae, feed on pollen, and three UK syrphid species feed strictly on pollen (syrphids, like all flies, cannot eat pollen directly due to the structure of their mouthparts, but can consume pollen contents that are dissolved in a fluid). Some species of fungus, including Fomes fomentarius, are able to break down grains of pollen as a secondary nutrition source that is particularly high in nitrogen. Pollen may be valuable diet supplement for detritivores, providing them with nutrients needed for growth, development and maturation. It was suggested that obtaining nutrients from pollen, deposited on the forest floor during periods of pollen rains, allows fungi to decompose nutritionally scarce litter. | Pollen | Wikipedia | 490 | 46980 | https://en.wikipedia.org/wiki/Pollen | Biology and health sciences | Plant reproduction | null |
Some species of Heliconius butterflies consume pollen as adults, which appears to be a valuable nutrient source, and these species are more distasteful to predators than the non-pollen consuming species.
Although bats, butterflies, and hummingbirds are not pollen eaters per se, their consumption of nectar in flowers is an important aspect of the pollination process.
In humans
Bee pollen for human consumption is marketed as a food ingredient and as a dietary supplement. The largest constituent is carbohydrates, with protein content ranging from 7 to 35 percent depending on the plant species collected by bees.
Honey produced by bees from natural sources contains pollen derived p-coumaric acid, an antioxidant and natural bactericide that is also present in a wide variety of plants and plant-derived food products.
The U.S. Food and Drug Administration (FDA) has not found any harmful effects of bee pollen consumption, except for the usual allergies. However, FDA does not allow bee pollen marketers in the United States to make health claims about their produce, as no scientific basis for these has ever been proven. Furthermore, there are possible dangers not only from allergic reactions but also from contaminants such as pesticides and from fungi and bacteria growth related to poor storage procedures. A manufacturers's claim that pollen collecting helps the bee colonies is also controversial.
Pine pollen () is traditionally consumed in Korea as an ingredient in sweets and beverages. Māori of precolonial New Zealand would gather pollen of Typha orientalis to make a special bread called pungapunga.
Parasites
The growing industries in pollen harvesting for human and bee consumption rely on harvesting pollen baskets from honey bees as they return to their hives using a pollen trap. When this pollen has been tested for parasites, it has been found that a multitude of viruses and eukaryotic parasites are present in the pollen. It is currently unclear if the parasites are introduced by the bee that collected the pollen or if it is from the flower. Though this is not likely to pose a risk to humans, it is a major issue for the bumblebee rearing industry that relies on thousands of tonnes of honey bee collected pollen per year. Several sterilization methods have been employed, though no method has been 100% effective at sterilisation without reducing the nutritional value of the pollen
Forensic palynology | Pollen | Wikipedia | 480 | 46980 | https://en.wikipedia.org/wiki/Pollen | Biology and health sciences | Plant reproduction | null |
In forensic biology, pollen can tell a lot about where a person or object has been, because regions of the world, or even more particular locations such a certain set of bushes, will have a distinctive collection of pollen species. Pollen evidence can also reveal the season in which a particular object picked up the pollen. Pollen has been used to trace activity at mass graves in Bosnia, catch a burglar who brushed against a Hypericum bush during a crime, and has even been proposed as an additive for bullets to enable tracking them.
Spiritual purposes
In some Native American religions, pollen was used in prayers and rituals to symbolize life and renewal by sanctifying objects, dancing grounds, trails, and sandpaintings. It may also be sprinkled over heads or in mouths. Many Navajo people believed the body became holy when it traveled over a trail sprinkled with pollen.
Pollen grain staining
For agricultural research purposes, assessing the viability of pollen grains can be necessary and illuminating. A very common, efficient method to do so is known as Alexander's stain. This differential stain consists of ethanol, malachite green, distilled water, glycerol, phenol, chloral hydrate, acid fuchsin, orange G, and glacial acetic acid. (A less-toxic variation omits the phenol and chloral hydrate.) In angiosperms and gymnosperms non-aborted pollen grain will appear red or pink, and aborted pollen grains will appear blue or slightly green. | Pollen | Wikipedia | 316 | 46980 | https://en.wikipedia.org/wiki/Pollen | Biology and health sciences | Plant reproduction | null |
Scutum is a small constellation. Its name is Latin for shield, and it was originally named Scutum Sobiescianum by Johannes Hevelius in 1684. Located just south of the celestial equator, its four brightest stars form a narrow diamond shape. It is one of the 88 IAU designated constellations defined in 1922.
History
Scutum was named in 1684 by Polish astronomer Johannes Hevelius (Jan Heweliusz), who originally named it Scutum Sobiescianum (Shield of Sobieski) to commemorate the victory of the Christian forces led by Polish King John III Sobieski (Jan III Sobieski) in the Battle of Vienna in 1683. Later, the name was shortened to Scutum.
Five bright stars of Scutum (α Sct, β Sct, δ Sct, ε Sct and η Sct) were previously known as 1, 6, 2, 3, and 9 Aquilae respectively.
The constellation of Scutum was adopted by the International Astronomical Union in 1922 as one of the 88 constellations covering the entire sky, with the official abbreviation of "Sct". The constellation boundaries are defined by a quadrilateral. In the equatorial coordinate system, the right ascension coordinates of these borders lie between and , while the declination coordinates are between −3.83° and −15.94°.
Coincidentally, the Chinese also associated these stars with battle armor, incorporating them into the larger asterism known as Tien Pien, i.e., the Heavenly Casque (or Helmet).
Features
Stars
Scutum is not a bright constellation, with the brightest star, Alpha Scuti, being a K-type giant star at magnitude 3.85. However, some stars are notable in the constellation. Beta Scuti is the second brightest at magnitude 4.22, followed by Delta Scuti at magnitude 4.72. It is also known as 6 Aquilae. Beta Scuti is a binary system, with the primary with a spectral type similar to the Sun, although it is 1,270 times brighter. Delta Scuti is a bluish white giant star, which is now coming at the direction of the Solar System. Within 1.3 million years it will come as close to 10 light years from Earth, and will be much brighter than Sirius by that time. | Scutum (constellation) | Wikipedia | 486 | 46981 | https://en.wikipedia.org/wiki/Scutum%20%28constellation%29 | Physical sciences | Other | Astronomy |
UY Scuti is a red supergiant and is also one of the largest stars currently known with a radius over 900 times that of the Sun. RSGC1-F01 is another red supergiant whose radius is over 1,450 times that of the Sun. Scutum contains several clusters of supergiant stars, including RSGC1, Stephenson 2 and RSGC3.
Deep sky objects
Although not a large constellation, Scutum contains several open clusters, as well as a globular cluster and a planetary nebula. The two best known deep sky objects in Scutum are M11 (the Wild Duck Cluster) and the open cluster M26 (NGC 6694). The globular cluster NGC 6712 and the planetary nebula IC 1295 can be found in the eastern part of the constellation, only 24 arcminutes apart.
The most prominent open cluster in Scutum is the Wild Duck Cluster, M11. It was named by William Henry Smyth in 1844 for its resemblance in the eyepiece to a flock of ducks in flight. The cluster, 6200 light-years from Earth and 20 light-years in diameter, contains approximately 3000 stars, making it a particularly rich cluster. It is around 220 million years old, although some studies give older estimates. Estimates for the mass of the star cluster range from to .
Space exploration
The space probe Pioneer 11 is moving in the direction of this constellation. It will not near the closest star in this constellation for over a million years at its present speed, by which time its batteries will be long dead. | Scutum (constellation) | Wikipedia | 322 | 46981 | https://en.wikipedia.org/wiki/Scutum%20%28constellation%29 | Physical sciences | Other | Astronomy |
A buffer solution is a solution where the pH does not change significantly on dilution or if an acid or base is added at constant temperature. Its pH changes very little when a small amount of strong acid or base is added to it. Buffer solutions are used as a means of keeping pH at a nearly constant value in a wide variety of chemical applications. In nature, there are many living systems that use buffering for pH regulation. For example, the bicarbonate buffering system is used to regulate the pH of blood, and bicarbonate also acts as a buffer in the ocean.
Principles of buffering
Buffer solutions resist pH change because of a chemical equilibrium between the weak acid HA and its conjugate base A−:
When some strong acid is added to an equilibrium mixture of the weak acid and its conjugate base, hydrogen ions (H+) are added, and the equilibrium is shifted to the left, in accordance with Le Chatelier's principle. Because of this, the hydrogen ion concentration increases by less than the amount expected for the quantity of strong acid added.
Similarly, if strong alkali is added to the mixture, the hydrogen ion concentration decreases by less than the amount expected for the quantity of alkali added. In Figure 1, the effect is illustrated by the simulated titration of a weak acid with pKa = 4.7. The relative concentration of undissociated acid is shown in blue, and of its conjugate base in red. The pH changes relatively slowly in the buffer region, pH = pKa ± 1, centered at pH = 4.7, where [HA] = [A−]. The hydrogen ion concentration decreases by less than the amount expected because most of the added hydroxide ion is consumed in the reaction
and only a little is consumed in the neutralization reaction (which is the reaction that results in an increase in pH)
Once the acid is more than 95% deprotonated, the pH rises rapidly because most of the added alkali is consumed in the neutralization reaction.
Buffer capacity
Buffer capacity is a quantitative measure of the resistance to change of pH of a solution containing a buffering agent with respect to a change of acid or alkali concentration. It can be defined as follows:
where is an infinitesimal amount of added base, or
where is an infinitesimal amount of added acid. pH is defined as −log10[H+], and d(pH) is an infinitesimal change in pH. | Buffer solution | Wikipedia | 506 | 46999 | https://en.wikipedia.org/wiki/Buffer%20solution | Physical sciences | Concepts | Chemistry |
With either definition the buffer capacity for a weak acid HA with dissociation constant Ka can be expressed as
where [H+] is the concentration of hydrogen ions, and is the total concentration of added acid. Kw is the equilibrium constant for self-ionization of water, equal to 1.0. Note that in solution H+ exists as the hydronium ion H3O+, and further aquation of the hydronium ion has negligible effect on the dissociation equilibrium, except at very high acid concentration.
This equation shows that there are three regions of raised buffer capacity (see figure 2).
In the central region of the curve (coloured green on the plot), the second term is dominant, and Buffer capacity rises to a local maximum at pH = pKa. The height of this peak depends on the value of pKa. Buffer capacity is negligible when the concentration [HA] of buffering agent is very small and increases with increasing concentration of the buffering agent. Some authors show only this region in graphs of buffer capacity. Buffer capacity falls to 33% of the maximum value at pH = pKa ± 1, to 10% at pH = pKa ± 1.5 and to 1% at pH = pKa ± 2. For this reason the most useful range is approximately pKa ± 1. When choosing a buffer for use at a specific pH, it should have a pKa value as close as possible to that pH.
With strongly acidic solutions, pH less than about 2 (coloured red on the plot), the first term in the equation dominates, and buffer capacity rises exponentially with decreasing pH: This results from the fact that the second and third terms become negligible at very low pH. This term is independent of the presence or absence of a buffering agent.
With strongly alkaline solutions, pH more than about 12 (coloured blue on the plot), the third term in the equation dominates, and buffer capacity rises exponentially with increasing pH: This results from the fact that the first and second terms become negligible at very high pH. This term is also independent of the presence or absence of a buffering agent. | Buffer solution | Wikipedia | 441 | 46999 | https://en.wikipedia.org/wiki/Buffer%20solution | Physical sciences | Concepts | Chemistry |
Applications of buffers
The pH of a solution containing a buffering agent can only vary within a narrow range, regardless of what else may be present in the solution. In biological systems this is an essential condition for enzymes to function correctly. For example, in human blood a mixture of carbonic acid (HCO) and bicarbonate (HCO) is present in the plasma fraction; this constitutes the major mechanism for maintaining the pH of blood between 7.35 and 7.45. Outside this narrow range (7.40 ± 0.05 pH unit), acidosis and alkalosis metabolic conditions rapidly develop, ultimately leading to death if the correct buffering capacity is not rapidly restored.
If the pH value of a solution rises or falls too much, the effectiveness of an enzyme decreases in a process, known as denaturation, which is usually irreversible. The majority of biological samples that are used in research are kept in a buffer solution, often phosphate buffered saline (PBS) at pH 7.4.
In industry, buffering agents are used in fermentation processes and in setting the correct conditions for dyes used in colouring fabrics. They are also used in chemical analysis and calibration of pH meters.
Simple buffering agents
{| class="wikitable"
! Buffering agent !! pKa !! Useful pH range
|-
| Citric acid || 3.13, 4.76, 6.40 || 2.1–7.4
|-
| Acetic acid || 4.8 || 3.8–5.8
|-
| KH2PO4 || 7.2 || 6.2–8.2
|-
| CHES || 9.3 || 8.3–10.3
|-
| Borate || 9.24 || 8.25–10.25
|}
For buffers in acid regions, the pH may be adjusted to a desired value by adding a strong acid such as hydrochloric acid to the particular buffering agent. For alkaline buffers, a strong base such as sodium hydroxide may be added. Alternatively, a buffer mixture can be made from a mixture of an acid and its conjugate base. For example, an acetate buffer can be made from a mixture of acetic acid and sodium acetate. Similarly, an alkaline buffer can be made from a mixture of the base and its conjugate acid. | Buffer solution | Wikipedia | 507 | 46999 | https://en.wikipedia.org/wiki/Buffer%20solution | Physical sciences | Concepts | Chemistry |
"Universal" buffer mixtures
By combining substances with pKa values differing by only two or less and adjusting the pH, a wide range of buffers can be obtained. Citric acid is a useful component of a buffer mixture because it has three pKa values, separated by less than two. The buffer range can be extended by adding other buffering agents. The following mixtures (McIlvaine's buffer solutions) have a buffer range of pH 3 to 8.
{| class="wikitable"
! 0.2 M Na2HPO4 (mL)
! 0.1 M citric acid (mL)
! pH
|-
| 20.55
| 79.45
| style="background:#ff0000; color:white" | 3.0
|-
| 38.55
| 61.45
| style="background:#ff7777; color:white" |4.0
|-
| 51.50
| 48.50
| style="background:#ff7700;" | 5.0
|-
| 63.15
| 36.85
| style="background:#ffff00;" |6.0
|-
| 82.35
| 17.65
| style="background:#007777; color:white" | 7.0
|-
| 97.25
| 2.75
|style="background:#0077ff; color:white" | 8.0
|}
A mixture containing citric acid, monopotassium phosphate, boric acid, and diethyl barbituric acid can be made to cover the pH range 2.6 to 12.
Other universal buffers are the Carmody buffer and the Britton–Robinson buffer, developed in 1931.
Common buffer compounds used in biology
For effective range see Buffer capacity, above. Also see Good's buffers for the historic design principles and favourable properties of these buffer substances in biochemical applications.
Calculating buffer pH
Monoprotic acids
First write down the equilibrium expression | Buffer solution | Wikipedia | 420 | 46999 | https://en.wikipedia.org/wiki/Buffer%20solution | Physical sciences | Concepts | Chemistry |
This shows that when the acid dissociates, equal amounts of hydrogen ion and anion are produced. The equilibrium concentrations of these three components can be calculated in an ICE table (ICE standing for "initial, change, equilibrium").
{| class="wikitable"
|+ ICE table for a monoprotic acid
|-
!
! [HA] !! [A−] !! [H+]
|-
! I
| C0 || 0 || y
|-
! C
| −x || x || x
|-
! E
| C0 − x || x || x + y
|}
The first row, labelled I, lists the initial conditions: the concentration of acid is C0, initially undissociated, so the concentrations of A− and H+ would be zero; y is the initial concentration of added strong acid, such as hydrochloric acid. If strong alkali, such as sodium hydroxide, is added, then y will have a negative sign because alkali removes hydrogen ions from the solution. The second row, labelled C for "change", specifies the changes that occur when the acid dissociates. The acid concentration decreases by an amount −x, and the concentrations of A− and H+ both increase by an amount +x. This follows from the equilibrium expression. The third row, labelled E for "equilibrium", adds together the first two rows and shows the concentrations at equilibrium.
To find x, use the formula for the equilibrium constant in terms of concentrations:
Substitute the concentrations with the values found in the last row of the ICE table:
Simplify to
With specific values for C0, Ka and y, this equation can be solved for x. Assuming that pH = −log10[H+], the pH can be calculated as pH = −log10(x + y).
Polyprotic acids | Buffer solution | Wikipedia | 389 | 46999 | https://en.wikipedia.org/wiki/Buffer%20solution | Physical sciences | Concepts | Chemistry |
Polyprotic acids are acids that can lose more than one proton. The constant for dissociation of the first proton may be denoted as Ka1, and the constants for dissociation of successive protons as Ka2, etc. Citric acid is an example of a polyprotic acid H3A, as it can lose three protons.
{| class="wikitable" style="width: 230px;
|+ Stepwise dissociation constants
|-
! |Equilibrium!!Citric acid
|-
| H3A H2A− + H+||pKa1 = 3.13
|-
| H2A− HA2− + H+|| pKa2 = 4.76
|-
| HA2− A3− + H+|| pKa3 = 6.40
|}
When the difference between successive pKa values is less than about 3, there is overlap between the pH range of existence of the species in equilibrium. The smaller the difference, the more the overlap. In the case of citric acid, the overlap is extensive and solutions of citric acid are buffered over the whole range of pH 2.5 to 7.5.
Calculation of the pH with a polyprotic acid requires a speciation calculation to be performed. In the case of citric acid, this entails the solution of the two equations of mass balance:
CA is the analytical concentration of the acid, CH is the analytical concentration of added hydrogen ions, βq are the cumulative association constants. Kw is the constant for self-ionization of water. There are two non-linear simultaneous equations in two unknown quantities [A3−] and [H+]. Many computer programs are available to do this calculation. The speciation diagram for citric acid was produced with the program HySS. | Buffer solution | Wikipedia | 381 | 46999 | https://en.wikipedia.org/wiki/Buffer%20solution | Physical sciences | Concepts | Chemistry |
N.B. The numbering of cumulative, overall constants is the reverse of the numbering of the stepwise, dissociation constants.
{| class="wikitable"
|+ Relationship between cumulative association constant (β) values and stepwise dissociation constant (K) values for a tribasic acid.
! Equilibrium!! Relationship
|-
| A3− + H+ AH2+||Log β1= pka3
|-
| A3− + 2H+ AH2+||Log β2 =pka2 + pka3
|-
| A3− + 3H+ AH3||Log β3 = pka1 + pka2 + pka3
|}
Cumulative association constants are used in general-purpose computer programs such as the one used to obtain the speciation diagram above. | Buffer solution | Wikipedia | 175 | 46999 | https://en.wikipedia.org/wiki/Buffer%20solution | Physical sciences | Concepts | Chemistry |
In physical chemistry, the Arrhenius equation is a formula for the temperature dependence of reaction rates. The equation was proposed by Svante Arrhenius in 1889, based on the work of Dutch chemist Jacobus Henricus van 't Hoff who had noted in 1884 that the van 't Hoff equation for the temperature dependence of equilibrium constants suggests such a formula for the rates of both forward and reverse reactions. This equation has a vast and important application in determining the rate of chemical reactions and for calculation of energy of activation. Arrhenius provided a physical justification and interpretation for the formula. Currently, it is best seen as an empirical relationship. It can be used to model the temperature variation of diffusion coefficients, population of crystal vacancies, creep rates, and many other thermally induced processes and reactions. The Eyring equation, developed in 1935, also expresses the relationship between rate and energy.
Formulation
The Arrhenius equation describes the exponential dependence of the rate constant of a chemical reaction on the absolute temperature as
where
is the rate constant (frequency of collisions resulting in a reaction),
is the absolute temperature,
is the pre-exponential factor or Arrhenius factor or frequency factor. Arrhenius originally considered A to be a temperature-independent constant for each chemical reaction. However more recent treatments include some temperature dependence – see below.
is the molar activation energy for the reaction,
is the universal gas constant.
Alternatively, the equation may be expressed as
where
is the activation energy for the reaction (in the same unit as kBT),
is the Boltzmann constant.
The only difference is the unit of : the former form uses energy per mole, which is common in chemistry, while the latter form uses energy per molecule directly, which is common in physics.
The different units are accounted for in using either the gas constant, , or the Boltzmann constant, , as the multiplier of temperature . | Arrhenius equation | Wikipedia | 394 | 47011 | https://en.wikipedia.org/wiki/Arrhenius%20equation | Physical sciences | Kinetics | Chemistry |
The unit of the pre-exponential factor are identical to those of the rate constant and will vary depending on the order of the reaction. If the reaction is first order it has the unit s−1, and for that reason it is often called the frequency factor or attempt frequency of the reaction. Most simply, is the number of collisions that result in a reaction per second, is the number of collisions (leading to a reaction or not) per second occurring with the proper orientation to react and is the probability that any given collision will result in a reaction. It can be seen that either increasing the temperature or decreasing the activation energy (for example through the use of catalysts) will result in an increase in rate of reaction.
Given the small temperature range of kinetic studies, it is reasonable to approximate the activation energy as being independent of the temperature. Similarly, under a wide range of practical conditions, the weak temperature dependence of the pre-exponential factor is negligible compared to the temperature dependence of the factor ; except in the case of "barrierless" diffusion-limited reactions, in which case the pre-exponential factor is dominant and is directly observable.
With this equation it can be roughly estimated that the rate of reaction increases by a factor of about 2 to 3 for every 10 °C rise in temperature, for common values of activation energy and temperature range.
The factor denotes the fraction of molecules with energy greater than or equal to .
Derivation
Van't Hoff argued that the temperature of a reaction and the standard equilibrium constant exhibit the relation:
where denotes the apposite standard internal energy change value.
Let and respectively denote the forward and backward reaction rates of the reaction of interest, then
, an equation from which naturally follows.
Substituting the expression for in eq.(), we obtain .
The preceding equation can be broken down into the following two equations:
and
where and are the activation energies associated with the forward and backward reactions respectively, with .
Experimental findings suggest that the constants in eq.() and eq.() can be treated as being equal to zero, so that and
Integrating these equations and taking the exponential yields the results and , where each pre-exponential factor or is mathematically the exponential of the constant of integration for the respective indefinite integral in question.
Arrhenius plot
Taking the natural logarithm of Arrhenius equation yields:
Rearranging yields:
This has the same form as an equation for a straight line:
where x is the reciprocal of T. | Arrhenius equation | Wikipedia | 506 | 47011 | https://en.wikipedia.org/wiki/Arrhenius%20equation | Physical sciences | Kinetics | Chemistry |
So, when a reaction has a rate constant obeying the Arrhenius equation, a plot of ln k versus T−1 gives a straight line, whose slope and intercept can be used to determine Ea and A respectively. This procedure is common in experimental chemical kinetics. The activation energy is simply obtained by multiplying by (−R) the slope of the straight line drawn from a plot of ln k versus (1/T):
Modified Arrhenius equation
The modified Arrhenius equation makes explicit the temperature dependence of the pre-exponential factor. The modified equation is usually of the form
The original Arrhenius expression above corresponds to . Fitted rate constants typically lie in the range . Theoretical analyses yield various predictions for n. It has been pointed out that "it is not feasible to establish, on the basis of temperature studies of the rate constant, whether the predicted T1/2 dependence of the pre-exponential factor is observed experimentally". However, if additional evidence is available, from theory and/or from experiment (such as density dependence), there is no obstacle to incisive tests of the Arrhenius law.
Another common modification is the stretched exponential form
where β is a dimensionless number of order 1. This is typically regarded as a purely empirical correction or fudge factor to make the model fit the data, but can have theoretical meaning, for example showing the presence of a range of activation energies or in special cases like the Mott variable range hopping.
Theoretical interpretation
Arrhenius's concept of activation energy
Arrhenius argued that for reactants to transform into products, they must first acquire a minimum amount of energy, called the activation energy Ea. At an absolute temperature T, the fraction of molecules that have a kinetic energy greater than Ea can be calculated from statistical mechanics. The concept of activation energy explains the exponential nature of the relationship, and in one way or another, it is present in all kinetic theories.
The calculations for reaction rate constants involve an energy averaging over a Maxwell–Boltzmann distribution with as lower bound and so are often of the type of incomplete gamma functions, which turn out to be proportional to .
Collision theory | Arrhenius equation | Wikipedia | 447 | 47011 | https://en.wikipedia.org/wiki/Arrhenius%20equation | Physical sciences | Kinetics | Chemistry |
One approach is the collision theory of chemical reactions, developed by Max Trautz and William Lewis in the years 1916–18. In this theory, molecules are supposed to react if they collide with a relative kinetic energy along their line of centers that exceeds Ea. The number of binary collisions between two unlike molecules per second per unit volume is found to be
where NA is the Avogadro constant, dAB is the average diameter of A and B, T is the temperature which is multiplied by the Boltzmann constant kB to convert to energy, and μAB is the reduced mass.
The rate constant is then calculated as , so that the collision theory predicts that the pre-exponential factor is equal to the collision number zAB. However for many reactions this agrees poorly with experiment, so the rate constant is written instead as . Here is an empirical steric factor, often much less than 1.00, which is interpreted as the fraction of sufficiently energetic collisions in which the two molecules have the correct mutual orientation to react.
Transition state theory
The Eyring equation, another Arrhenius-like expression, appears in the "transition state theory" of chemical reactions, formulated by Eugene Wigner, Henry Eyring, Michael Polanyi and M. G. Evans in the 1930s. The Eyring equation can be written:
where is the Gibbs energy of activation, is the entropy of activation, is the enthalpy of activation, is the Boltzmann constant, and is the Planck constant.
At first sight this looks like an exponential multiplied by a factor that is linear in temperature. However, free energy is itself a temperature dependent quantity. The free energy of activation is the difference of an enthalpy term and an entropy term multiplied by the absolute temperature. The pre-exponential factor depends primarily on the entropy of activation. The overall expression again takes the form of an Arrhenius exponential (of enthalpy rather than energy) multiplied by a slowly varying function of T. The precise form of the temperature dependence depends upon the reaction, and can be calculated using formulas from statistical mechanics involving the partition functions of the reactants and of the activated complex. | Arrhenius equation | Wikipedia | 438 | 47011 | https://en.wikipedia.org/wiki/Arrhenius%20equation | Physical sciences | Kinetics | Chemistry |
Limitations of the idea of Arrhenius activation energy
Both the Arrhenius activation energy and the rate constant k are experimentally determined, and represent macroscopic reaction-specific parameters that are not simply related to threshold energies and the success of individual collisions at the molecular level. Consider a particular collision (an elementary reaction) between molecules A and B. The collision angle, the relative translational energy, the internal (particularly vibrational) energy will all determine the chance that the collision will produce a product molecule AB. Macroscopic measurements of E and k are the result of many individual collisions with differing collision parameters. To probe reaction rates at molecular level, experiments are conducted under near-collisional conditions and this subject is often called molecular reaction dynamics.
Another situation where the explanation of the Arrhenius equation parameters falls short is in heterogeneous catalysis, especially for reactions that show Langmuir-Hinshelwood kinetics. Clearly, molecules on surfaces do not "collide" directly, and a simple molecular cross-section does not apply here. Instead, the pre-exponential factor reflects the travel across the surface towards the active site.
There are deviations from the Arrhenius law during the glass transition in all classes of glass-forming matter. The Arrhenius law predicts that the motion of the structural units (atoms, molecules, ions, etc.) should slow down at a slower rate through the glass transition than is experimentally observed. In other words, the structural units slow down at a faster rate than is predicted by the Arrhenius law. This observation is made reasonable assuming that the units must overcome an energy barrier by means of a thermal activation energy. The thermal energy must be high enough to allow for translational motion of the units which leads to viscous flow of the material. | Arrhenius equation | Wikipedia | 372 | 47011 | https://en.wikipedia.org/wiki/Arrhenius%20equation | Physical sciences | Kinetics | Chemistry |
An incandescent light bulb, incandescent lamp or incandescent light globe is an electric light with a filament that is heated until it glows. The filament is enclosed in a glass bulb that is either evacuated or filled with inert gas to protect the filament from oxidation. Electric current is supplied to the filament by terminals or wires embedded in the glass. A bulb socket provides mechanical support and electrical connections.
Incandescent bulbs are manufactured in a wide range of sizes, light output, and voltage ratings, from 1.5 volts to about 300 volts. They require no external regulating equipment, have low manufacturing costs, and work equally well on either alternating current or direct current. As a result, the incandescent bulb became widely used in household and commercial lighting, for portable lighting such as table lamps, car headlamps, and flashlights, and for decorative and advertising lighting.
Incandescent bulbs are much less efficient than other types of electric lighting. Less than 5% of the energy they consume is converted into visible light; the rest is lost as heat. The luminous efficacy of a typical incandescent bulb for 120 V operation is 16 lumens per watt (lm/W), compared with 60 lm/W for a compact fluorescent bulb or 100 lm/W for typical white LED lamps.
The heat produced by filaments is used in some applications, such as heat lamps in incubators, lava lamps, Edison effect bulbs, and the Easy-Bake Oven toy. Quartz envelope halogen infrared heaters are used for industrial processes such as paint curing and space heating.
Incandescent bulbs typically have shorter lifetimes compared to other types of lighting; around 1,000 hours for home light bulbs versus typically 10,000 hours for compact fluorescents and 20,000–30,000 hours for lighting LEDs. Most incandescent bulbs can be replaced by fluorescent lamps, high-intensity discharge lamps, and light-emitting diode lamps (LED). Some governments have begun a phase-out of incandescent light bulbs to reduce energy consumption. | Incandescent light bulb | Wikipedia | 435 | 47139 | https://en.wikipedia.org/wiki/Incandescent%20light%20bulb | Technology | Electricity generation and distribution | null |
History
Historians Robert Friedel and Paul Israel list inventors of incandescent lamps prior to Joseph Swan and Thomas Edison of General Electric. They conclude that Edison's version was the first practical implementation, able to outstrip the others because of a combination of four factors: an effective incandescent material; a vacuum higher than other implementations which was achieved through the use of a Sprengel pump; a high resistance that made power distribution from a centralized source economically viable, and the development of the associated components required for a large-scale lighting system.
Historian Thomas Hughes has attributed Edison's success to his development of an entire, integrated system of electric lighting.
Early pre-commercial research
In 1761, Ebenezer Kinnersley demonstrated heating a wire to incandescence. However such wires tended to melt or oxidize very rapidly (burn) in the presence of air. Limelight became a popular form of stage lighting in the early 19th century, by heating a piece of calcium oxide to incandescence with an oxyhydrogen torch.
In 1802, Humphry Davy used what he described as "a battery of immense size", consisting of 2,000 cells housed in the basement of the Royal Institution of Great Britain, to create an incandescent light by passing the current through a thin strip of platinum, chosen because the metal had an extremely high melting point. It was not bright enough nor did it last long enough to be practical, but it was the precedent behind the efforts of scores of experimenters over the next 75 years. Davy also demonstrated the electric arc, by passing high current between two pieces of charcoal.
For the next 40 years much research was given to turning the carbon arc lamp into a practical means of lighting. The carbon arc itself was dim and violet in color, emitting most of its energy in the ultraviolet, but the positive electrode was heated to just below the melting point of carbon and glowed very brightly with incandescence very close to that of sunlight. Arc lamps burned up their carbon rods very rapidly, expelled dangerous carbon monoxide, and tended to produce outputs in the tens of kilowatts. Therefore, they were only practical for lighting large areas, so researchers continued to search for a way to make lamps suitable for home use.
Over the first three-quarters of the 19th century, many experimenters worked with various combinations of platinum or iridium wires, carbon rods, and evacuated or semi-evacuated enclosures. Many of these devices were demonstrated and some were patented. | Incandescent light bulb | Wikipedia | 509 | 47139 | https://en.wikipedia.org/wiki/Incandescent%20light%20bulb | Technology | Electricity generation and distribution | null |
In 1835, James Bowman Lindsay demonstrated a constant electric light at a public meeting in Dundee, Scotland. He stated that he could "read a book at a distance of one and a half feet". However he did not develop the electric light any further.
In 1838, Belgian lithographer Marcellin Jobard invented an incandescent light bulb with a vacuum atmosphere using a carbon filament.
In 1840, British scientist Warren De la Rue enclosed a coiled platinum filament in a vacuum tube and passed an electric current through it. The design was based on the concept that the high melting point of platinum would allow it to operate at high temperatures and that the evacuated chamber would contain fewer gas molecules to react with the platinum, improving its longevity. Although a workable design, the cost of the platinum made it impractical for commercial use.
In 1841, Frederick de Moleyns of England was granted the first patent for an incandescent lamp, with a design using platinum wires contained within a vacuum bulb. He also used carbon.
In 1845, American John W. Starr patented an incandescent light bulb using carbon filaments. His invention was never produced commercially.
In 1851, Jean Eugène Robert-Houdin publicly demonstrated incandescent light bulbs on his estate in Blois, France. His light bulbs are on display in the museum of the Château de Blois.
In 1859, Moses G. Farmer built an electric incandescent light bulb using a platinum filament. Thomas Edison later saw one of these bulbs in a shop in Boston, and asked Farmer for advice on the electric light business.
In 1872, Russian Alexander Lodygin invented an incandescent light bulb and obtained a Russian patent in 1874. He used as a burner two carbon rods of diminished section in a glass receiver, hermetically sealed, and filled with nitrogen, electrically arranged so that the current could be passed to the second carbon when the first had been consumed. Later he lived in the US, changed his name to Alexander de Lodyguine and applied for and obtained patents for incandescent lamps having chromium, iridium, rhodium, ruthenium, osmium, molybdenum and tungsten filaments. | Incandescent light bulb | Wikipedia | 458 | 47139 | https://en.wikipedia.org/wiki/Incandescent%20light%20bulb | Technology | Electricity generation and distribution | null |
On 24 July 1874, a Canadian patent was filed by Henry Woodward and Mathew Evans for a lamp consisting of carbon rods mounted in a nitrogen-filled glass cylinder. They were unsuccessful at commercializing their lamp, and sold rights to their patent to Thomas Edison in 1879. (Edison needed ownership of the novel claim of lamps connected in a parallel circuit.) The government of Canada maintains that it is Woodward and Evans who invented the lightbulb.
On 4 March 1880, just five months after Edison's light bulb, Alessandro Cruto created his first incandescent lamp. Cruto produced a filament by deposition of graphite on thin platinum filaments, by heating it with an electric current in the presence of gaseous ethyl alcohol. Heating this platinum at high temperatures leaves behind thin filaments of platinum coated with pure graphite. By September 1881 he had achieved a successful version of this the first synthetic filament. The light bulb invented by Cruto lasted five hundred hours as opposed to the forty of Edison's original version. In 1882 Munich Electrical Exhibition in Bavaria, Germany Cruto's lamp was more efficient than the Edison's one and produced a better, white light.
In 1893, Heinrich Göbel claimed he had designed the first incandescent light bulb in 1854, with a thin carbonized bamboo filament of high resistance, platinum lead-in wires in an all-glass envelope, and a high vacuum. Judges of four courts raised doubts about the alleged Göbel anticipation, but there was never a decision in a final hearing due to the expiration of Edison's patent. Research work published in 2007 concluded that the story of the Göbel lamps in the 1850s is fictitious.
Commercialization
Carbon filament and vacuum
Joseph Swan (1828–1914) was a British physicist and chemist. In 1850, he began working with carbonized paper filaments in an evacuated glass bulb. By 1860, he was able to demonstrate a working device but the lack of a good vacuum and an adequate supply of electricity resulted in a short lifetime for the bulb and an inefficient source of light. By the mid-1870s better pumps had become available, and Swan returned to his experiments. | Incandescent light bulb | Wikipedia | 448 | 47139 | https://en.wikipedia.org/wiki/Incandescent%20light%20bulb | Technology | Electricity generation and distribution | null |
With the help of Charles Stearn, an expert on vacuum pumps, in 1878, Swan developed a method of processing that avoided the early bulb blackening. This received a British Patent in 1880. On 18 December 1878, a lamp using a slender carbon rod was shown at a meeting of the Newcastle Chemical Society, and Swan gave a working demonstration at their meeting on 17 January 1879. It was also shown to 700 who attended a meeting of the Literary and Philosophical Society of Newcastle upon Tyne on 3 February 1879. These lamps used a carbon rod from an arc lamp rather than a slender filament. Thus they had low resistance and required very large conductors to supply the necessary current, so they were not commercially practical, although they did furnish a demonstration of the possibilities of incandescent lighting with relatively high vacuum, a carbon conductor, and platinum lead-in wires. This bulb lasted about 40 hours.
Swan then turned his attention to producing a better carbon filament and the means of attaching its ends. He devised a method of treating cotton to produce 'parchmentised thread' in the early 1880s and obtained British Patent 4933 that same year. From this year he began installing light bulbs in homes and landmarks in England. His house, Underhill, Low Fell, Gateshead, was the first in the world to be lit by a lightbulb. In the early 1880s he had started his company. In 1881, the Savoy Theatre in the City of Westminster, London was lit by Swan incandescent lightbulbs, which was the first theatre, and the first public building in the world, to be lit entirely by electricity. The first street in the world to be lit by an incandescent lightbulb was Mosley Street, Newcastle upon Tyne, United Kingdom. It was lit by Joseph Swan's incandescent lamp on 3 February 1879. | Incandescent light bulb | Wikipedia | 376 | 47139 | https://en.wikipedia.org/wiki/Incandescent%20light%20bulb | Technology | Electricity generation and distribution | null |
Thomas Edison began serious research into developing a practical incandescent lamp in 1878. Edison filed his first patent application for "Improvement in Electric Lights" on 14 October 1878. After many experiments, first with carbon in the early 1880s and then with platinum and other metals, in the end Edison returned to a carbon filament. The first successful test was on 22 October 1879, and lasted 13.5 hours. Edison continued to improve this design and by 4 November 1879, filed for a US patent for an electric lamp using "a carbon filament or strip coiled and connected ... to platina contact wires." Although the patent described several ways of creating the carbon filament including using "cotton and linen thread, wood splints, papers coiled in various ways," Edison and his team later discovered that a carbonized bamboo filament could last more than 1200 hours. In 1880, the Oregon Railroad and Navigation Company steamer, Columbia, became the first application for Edison's incandescent electric lamps (it was also the first ship to use a dynamo).
Albon Man, a New York lawyer, started Electro-Dynamic Light Company in 1878 to exploit his patents and those of William Sawyer. Weeks later the United States Electric Lighting Company was organized. This company did not make their first commercial installation of incandescent lamps until the fall of 1880, at the Mercantile Safe Deposit Company in New York City, about six months after the Edison incandescent lamps had been installed on the Columbia. Hiram S. Maxim was the chief engineer at the US Electric Lighting Co. After the great success in the United States, the incandescent light bulb patented by Edison also began to gain widespread popularity in Europe as well; among other places, the first Edison light bulbs in the Nordic countries were installed at the weaving hall of the Finlayson's textile factory in Tampere, Finland in March 1882.
Lewis Latimer, employed at the time by Edison, developed an improved method of heat-treating carbon filaments which reduced breakage and allowed them to be molded into novel shapes, such as the characteristic "M" shape of Maxim filaments. On 17 January 1882, Latimer received a patent for the "Process of Manufacturing Carbons", an improved method for the production of light bulb filaments, which was purchased by the United States Electric Light Company. Latimer patented other improvements such as a better way of attaching filaments to their wire supports. | Incandescent light bulb | Wikipedia | 506 | 47139 | https://en.wikipedia.org/wiki/Incandescent%20light%20bulb | Technology | Electricity generation and distribution | null |
In Britain, the Edison and Swan companies merged into the Edison and Swan United Electric Company (later known as Ediswan, and ultimately incorporated into Thorn Lighting Ltd). Edison was initially against this combination, but Edison was eventually forced to cooperate and the merger was made. Eventually, Edison acquired all of Swan's interest in the company. Swan sold his US patent rights to the Brush Electric Company in June 1882.
The United States Patent Office gave a ruling 8 October 1883, that Edison's patents were based on the prior art of William Sawyer and were invalid. Litigation continued for a number of years. Eventually on 6 October 1889, a judge ruled that Edison's electric light improvement claim for "a filament of carbon of high resistance" was valid.
The main difficulty with evacuating the lamps was moisture inside the bulb, which split when the lamp was lit, with resulting oxygen attacking the filament. In the 1880s, phosphoric anhydride was used in combination with expensive mercury vacuum pumps. However, about 1893, Italian inventor (1865–1939), who lacked these pumps, discovered that phosphorus vapours did the job of chemically binding the remaining amounts of water and oxygen. In 1896 he patented a process of introducing red phosphorus as the so-called getter inside the bulb ), which allowed obtaining economic bulbs lasting 800 hours; his patent was acquired by Edison in 1898.
In 1897, German physicist and chemist Walther Nernst developed the Nernst lamp, a form of incandescent lamp that used a ceramic globar and did not require enclosure in a vacuum or inert gas. Twice as efficient as carbon filament lamps, Nernst lamps were briefly popular until overtaken by lamps using metal filaments.
Metal filament, inert gas | Incandescent light bulb | Wikipedia | 368 | 47139 | https://en.wikipedia.org/wiki/Incandescent%20light%20bulb | Technology | Electricity generation and distribution | null |
US575002A patent on 01.Dec.1897 to Alexander Lodyguine (Lodygin, Russia) describes filament made of rare metals, amongst them was tungsten. Lodygin invented a process where rare metals such as tungsten can be chemically treated and heat-vaporized onto an electrically heated thread-like wire (platinum, carbon, gold) acting as a temporary base or skeletal form. (US patent 575,002). Lodygin later sold the patent rights to GE.
In 1902, Siemens developed a tantalum lamp filament that was more efficient than even graphitized carbon filaments since they could operate at higher temperature. Since tantalum metal has a lower resistivity than carbon, the tantalum lamp filament was quite long and required multiple internal supports. The metal filament gradually shortened in use; the filaments were installed with large slack loops. Lamps used for several hundred hours became quite fragile. Metal filaments had the property of breaking and re-welding, though this would usually decrease resistance and shorten the life of the filament. General Electric bought the rights to use tantalum filaments and produced them in the US until 1913.
From 1898 to around 1905, osmium was also used as a filament in lamps made by Carl Auer von Welsbach. The metal was so expensive that used lamps could be returned for partial credit. It could not be made for 110 V or 220 V so several lamps were wired in series for use on standard voltage circuits. These were primarily sold in Europe.
Tungsten filament
On 13 December 1904, Hungarian Sándor Just and Croatian Franjo Hanaman were granted a Hungarian patent (No. 34541) for a tungsten filament lamp that lasted longer and gave brighter light than the carbon filament. Tungsten filament lamps were first marketed by the Hungarian company Tungsram in 1904. This type is often called Tungsram-bulbs in many European countries. Filling a bulb with an inert gas such as argon or nitrogen slows down the evaporation of the tungsten filament compared to operating it in a vacuum. This allows for greater temperatures and therefore greater efficacy with less reduction in filament life. | Incandescent light bulb | Wikipedia | 472 | 47139 | https://en.wikipedia.org/wiki/Incandescent%20light%20bulb | Technology | Electricity generation and distribution | null |
In 1906, William D. Coolidge developed a method of making "ductile tungsten" from sintered tungsten which could be made into filaments while working for General Electric Company. By 1911 General Electric had begun selling incandescent light bulbs with ductile tungsten wire.
In 1913, Irving Langmuir found that filling a lamp with inert gas (nitrogen at first, and later argon) instead of a vacuum resulted in twice the luminous efficacy and reduced bulb blackening.. He patented his device on April 18, 1916.
In 1917, Burnie Lee Benbow was granted a patent for the coiled coil filament, in which a coiled filament is then itself wrapped into a coil by use of a mandrel. In 1921, Junichi Miura created the first double-coil bulb using a coiled coil tungsten filament while working for Hakunetsusha (a predecessor of Toshiba). At the time, machinery to mass-produce coiled coil filaments did not exist. Hakunetsusha developed a method to mass-produce coiled coil filaments by 1936.
Between 1924 and the outbreak of the Second World War, the Phoebus cartel attempted to fix prices and sales quotas for bulb manufacturers outside of North America.
In 1925, Marvin Pipkin, an American chemist, patented a process for frosting the inside of lamp bulbs without weakening them. In 1947, he patented a process for coating the inside of lamps with silica.
In 1930, Hungarian Imre Bródy filled lamps with krypton gas rather than argon, and designed a process to obtain krypton from air. Production of krypton filled lamps based on his invention started at Ajka in 1937, in a factory co-designed by Polányi and Hungarian-born physicist Egon Orowan.
By 1964, improvements in efficiency and production of incandescent lamps had reduced the cost of providing a given quantity of light by a factor of thirty, compared with the cost at introduction of Edison's lighting system. | Incandescent light bulb | Wikipedia | 418 | 47139 | https://en.wikipedia.org/wiki/Incandescent%20light%20bulb | Technology | Electricity generation and distribution | null |
Consumption of incandescent light bulbs grew rapidly in the US. In 1885, an estimated 300,000 general lighting service lamps were sold, all with carbon filaments. When tungsten filaments were introduced, about 50 million lamp sockets existed in the US. In 1914, 88.5 million lamps were used, (only 15% with carbon filaments), and by 1945, annual sales of lamps were 795 million (more than 5 lamps per person per year).
Efficacy and efficiency
Less than 5% of the power consumed by a typical incandescent light bulb is converted into visible light, with most of the rest being emitted as invisible infrared radiation. Light bulbs are rated by their luminous efficacy, which is the ratio of the amount of visible light emitted (luminous flux) to the electrical power consumed. Luminous efficacy is measured in lumens per watt (lm/W).
The luminous efficiency of a source is defined as the ratio of its luminous efficacy to the maximum possible luminous efficacy, which is 683 lm/W. An ideal white light source could produce about 250 lumens per watt, corresponding to a luminous efficiency of 37%.
For a given quantity of light, an incandescent light bulb consumes more power and emits more heat than most other types of electric light. In buildings where air conditioning is used, incandescent lamps' heat output increases load on the air conditioning system. While heat from lights will reduce the need to run a building's heating system, the latter can usually produce the same amount of heat at lower cost than incandescent lights.
The chart below lists the luminous efficacy and efficiency for several types of incandescent bulb. A longer chart in luminous efficacy compares a broader array of light sources.
Color rendering
The spectrum of light produced by an incandescent lamp closely approximates that of a black body radiator at the same temperature. The basis for light sources used as the standard for color perception is a tungsten incandescent lamp operating at a defined temperature. | Incandescent light bulb | Wikipedia | 414 | 47139 | https://en.wikipedia.org/wiki/Incandescent%20light%20bulb | Technology | Electricity generation and distribution | null |
Light sources such as fluorescent lamps, high-intensity discharge lamps and LED lamps have higher luminous efficiency. These devices produce light by luminescence. Their light has bands of characteristic wavelengths, without the "tail" of invisible infrared emissions, instead of the continuous spectrum produced by a thermal source. By careful selection of fluorescent phosphor coatings or filters which modify the spectral distribution, the spectrum emitted can be tuned to mimic the appearance of incandescent sources, or other different color temperatures of white light. When used for tasks sensitive to color, such as motion picture lighting, these sources may require particular techniques to duplicate the appearance of incandescent lighting. Metamerism describes the effect of different light spectrum distributions on the perception of color.
Cost of lighting
The initial cost of an incandescent bulb is small compared to the cost of the energy it uses over its lifetime. Incandescent bulbs have a shorter life than most other lighting, an important factor if replacement is inconvenient or expensive. Some types of lamp, including incandescent and fluorescent, emit less light as they age; this may be an inconvenience, or may reduce effective lifetime due to lamp replacement before total failure. A comparison of incandescent lamp operating cost with other light sources must include illumination requirements, cost of the lamp and labor cost to replace lamps (taking into account effective lamp lifetime), cost of electricity used, effect of lamp operation on heating and air conditioning systems. When used for lighting in houses and commercial buildings, the energy lost to heat can significantly increase the energy required by a building's air conditioning system. During the heating season heat produced by the bulbs is not wasted, although in most cases it is more cost effective to obtain heat from the heating system. Regardless, over the course of a year a more efficient lighting system saves energy in nearly all climates.
Measures to ban use
Since incandescent light bulbs use more energy than alternatives such as CFLs and LED lamps, many governments have introduced measures to ban their use, by setting minimum efficacy standards higher than can be achieved by incandescent lamps. Measures to ban light bulbs have been implemented in the European Union, the United States, Russia, Brazil, Argentina, Canada and Australia, among others. The European Commission has calculated that the ban contributes to to the economy and saves 40 TWh of electricity every year, translating in emission reductions of . | Incandescent light bulb | Wikipedia | 487 | 47139 | https://en.wikipedia.org/wiki/Incandescent%20light%20bulb | Technology | Electricity generation and distribution | null |
Objections to banning the use of incandescent light bulbs include the higher initial cost of alternatives and lower quality of light of fluorescent lamps. Some people have concerns about the health effects of fluorescent lamps.
Efforts to improve efficacy
Some research has been carried out to improve the efficacy of commercial incandescent lamps. In 2007, General Electric announced a high efficiency incandescent (HEI) lamp project, which they claimed would ultimately be as much as four times more efficient than current incandescents, although their initial production goal was to be approximately twice as efficient. The HEI program was terminated in 2008 due to slow progress.
US Department of Energy research at Sandia National Laboratories initially indicated the potential for dramatically improved efficiency from a photonic lattice filament. However, later work indicated that initially promising results were in error.
Prompted by legislation in various countries mandating increased bulb efficiency, hybrid incandescent bulbs have been introduced by Philips. The Halogena Energy Saver incandescents can produce about 23 lm/W; about 30 percent more efficient than traditional incandescents, by using a reflective capsule to reflect formerly wasted infrared radiation back to the filament from which some is re-emitted as visible light. This concept was pioneered by Duro-Test in 1980 with a commercial product that produced 29.8 lm/W. More advanced reflectors based on interference filters or photonic crystals can theoretically result in higher efficiency, up to a limit of about 270 lm/W (40% of the maximum efficacy possible). Laboratory proof-of-concept experiments have produced as much as 45 lm/W, approaching the efficacy of compact fluorescent bulbs.
Construction
Incandescent light bulbs consist of an air-tight glass enclosure (the envelope, or bulb) with a filament of tungsten wire inside the bulb, through which an electric current is passed. Contact wires and a base with two (or more) conductors provide electrical connections to the filament. Incandescent light bulbs usually contain a stem or glass mount anchored to the bulb's base that allows the electrical contacts to run through the envelope without air or gas leaks. Small wires embedded in the stem in turn support the filament and its lead wires. | Incandescent light bulb | Wikipedia | 455 | 47139 | https://en.wikipedia.org/wiki/Incandescent%20light%20bulb | Technology | Electricity generation and distribution | null |
An electric current heats the filament to typically , well below tungsten's melting point of . Filament temperatures depend on the filament type, shape, size, and amount of current drawn. The heated filament emits light that approximates a continuous spectrum. The useful part of the emitted energy is visible light, but most energy is given off as heat in the near-infrared wavelengths.
Bulbs
Most light bulbs have either clear or coated glass. Coated glass bulbs have kaolin clay blown in and electrostatically deposited on the interior of the bulb. The powder layer diffuses the light from the filament. Pigments may be added to the clay to adjust the color of the light emitted. Kaolin diffused bulbs are used extensively in interior lighting because of their comparatively gentle light. Other kinds of colored bulbs are also made, including the various colors used for "party bulbs", Christmas tree lights and other decorative lighting. These are created by coloring the glass with a dopant; which is often a metal like cobalt (blue) or chromium (green). Neodymium-containing glass is sometimes used to provide a more natural-appearing light.
The glass bulb of a general service lamp can reach temperatures between . Lamps intended for high power operation or used for heating purposes will have envelopes made of hard glass or fused quartz.
If a light bulb envelope leaks, the hot tungsten filament reacts with air, yielding an aerosol of brown tungsten nitride, brown tungsten dioxide, violet-blue tungsten pentoxide, and yellow tungsten trioxide that then gets deposited on the nearby surfaces or the bulb interior.
Gas fill
Most modern bulbs are filled with an inert gas to reduce evaporation of the filament and prevent its oxidation. The gas is at a pressure of about . | Incandescent light bulb | Wikipedia | 376 | 47139 | https://en.wikipedia.org/wiki/Incandescent%20light%20bulb | Technology | Electricity generation and distribution | null |
The gas reduces evaporation of the filament, but the fill must be chosen carefully to avoid introducing significant heat losses. For these properties, chemical inertness and high atomic or molecular weight is desirable. The presence of gas molecules knocks the liberated tungsten atoms back to the filament, reducing its evaporation and allowing it to be operated at higher temperature without reducing its life (or, for operating at the same temperature, prolongs the filament life). On the other hand, the presence of the gas leads to heat loss from the filament—and therefore efficiency loss due to reduced incandescence—by heat conduction and heat convection.
Early lamps used only a vacuum to protect the filament from oxygen. The vacuum increases evaporation of the filament but eliminates two modes of heat loss. Some small modern lamps use vacuum as well.
The most commonly used fills are:
Vacuum, used in small lamps. Provides best thermal insulation of the filament but does not protect against its evaporation. Used also in larger lamps where the outer bulb surface temperature has to be limited.
Argon (93%) and nitrogen (7%), where argon is used for its inertness, low thermal conductivity and low cost, and the nitrogen is added to increase the breakdown voltage and prevent arcing between parts of the filament
Nitrogen, used in some higher-power lamps, e.g. projection lamps, and where higher breakdown voltage is needed due to proximity of filament parts or lead-in wires
Krypton, which is more advantageous than argon due to its higher atomic weight and lower thermal conductivity (which also allows use of smaller bulbs), but its use is hindered by much higher cost, confining it mostly to smaller-size bulbs.
Krypton mixed with xenon, where xenon improves the gas properties further due to its higher atomic weight. Its use is however limited by its very high cost. The improvements by using xenon are modest in comparison to its cost.
Hydrogen, in special flashing lamps where rapid filament cooling is required; its high thermal conductivity is exploited here.
Halogen, a small amount mixed with inert gas. This is used in halogen lamps, which are a distinct type of incandescent lamp.
The gas fill must be free of traces of water, which greatly accelerates bulb blackening (see below). | Incandescent light bulb | Wikipedia | 506 | 47139 | https://en.wikipedia.org/wiki/Incandescent%20light%20bulb | Technology | Electricity generation and distribution | null |
The gas layer close to the filament (called the Langmuir layer) is stagnant, with heat transfer occurring only by conduction. Only at some distance does convection occur to carry heat to the bulb's envelope.
The orientation of the filament influences efficiency. Gas flow parallel to the filament, e.g., a vertically oriented bulb with vertical (or axial) filament, reduces convective losses.
The efficiency of the lamp increases with a larger filament diameter. Thin-filament, low-power bulbs benefit less from a fill gas, so are often only evacuated.
Early light bulbs with carbon filaments also used carbon monoxide, nitrogen, or mercury vapor. However, carbon filaments operate at lower temperatures than tungsten ones, so the effect of the fill gas was not significant as the heat losses offset any benefits.
Manufacturing
Early bulbs were laboriously assembled by hand. After automatic machinery was developed, the cost of bulbs fell. Until 1910, when Libbey's Westlake machine went into production, bulbs were generally produced by a team of three workers (two gatherers and a master gaffer) blowing the bulbs into wooden or cast-iron molds, coated with a paste. Around 150 bulbs per hour were produced by the hand-blowing process in the 1880s at Corning Glass Works.
The Westlake machine, developed by Libbey Glass, was based on an adaptation of the Owens-Libbey bottle-blowing machine. Corning Glass Works soon began developing competing automated bulb-blowing machines, the first of which to be used in production was the E-Machine.
Ribbon machine
Corning continued developing automated bulb-production machines, installing the Ribbon Machine in 1926 in its Wellsboro, Pennsylvania, factory. The Ribbon Machine surpassed any previous attempts to automate bulb production and was used to produce incandescent bulbs into the 21st century. The inventor, William Woods, along with his colleague at Corning Glass Works, David E. Gray, had created a machine that by 1939 was turning out 1,000 bulbs per minute. | Incandescent light bulb | Wikipedia | 428 | 47139 | https://en.wikipedia.org/wiki/Incandescent%20light%20bulb | Technology | Electricity generation and distribution | null |
The Ribbon Machine works by passing a continuous ribbon of glass along a conveyor belt, heated in a furnace, and then blown by precisely aligned air nozzles through holes in the conveyor belt into molds. Thus the glass bulbs or envelopes are created. A typical machine of this sort can produce anywhere from 50,000 to 120,000 bulbs per hour, depending on the size of the bulb. By the 1970s, 15 ribbon machines installed in factories around the world produced the entire supply of incandescent bulbs. The filament and its supports are assembled on a glass stem, which is then fused to the bulb. The air is pumped out of the bulb, and the evacuation tube in the stem press is sealed by a flame. The bulb is then inserted into the lamp base, and the whole assembly tested. The 2016 closing of Osram-Sylvania's Wellsboro, Pennsylvania plant meant that one of the last remaining ribbon machines in the United States was shut down.
Filament
Carbon has the highest melting point of any element, and in carbon arc lamps it had been demonstrated to produce incandescence fairly close to that of sunlight. However, carbon has a tendency to sublimate before reaching its melting point depending on pressure, which led to rapid blackening of vacuumed bulbs. The first commercially successful light bulb filaments were made from carbonized paper or bamboo. Carbon filaments have a negative temperature coefficient of resistance—as they get hotter, their electrical resistance decreases. This made the lamp sensitive to fluctuations in the power supply, since a small increase of voltage would cause the filament to heat up, reducing its resistance and causing it to draw even more power and heat even further.
Carbon filaments were "flashed" by heating in a hydrocarbon vapor (usually gasoline), to improve their strength and uniformity. Metallized or "graphitized" filaments were first heated to high temperature to transform them into graphite, which further strengthened and smoothed the filament. These filaments have a positive temperature coefficient, like a metallic conductor, which stabilized the lamps operating properties against minor variations in supply voltage. | Incandescent light bulb | Wikipedia | 439 | 47139 | https://en.wikipedia.org/wiki/Incandescent%20light%20bulb | Technology | Electricity generation and distribution | null |
Metal filaments were tried in 1897 and started to displace carbon starting around 1904. Tungsten has the highest available melting point, but brittleness was a big obstacle. By 1910, a process was developed by William D. Coolidge at General Electric for production of a ductile form of tungsten. The process required pressing tungsten powder into bars, then several steps of sintering, swaging, and then wire drawing. It was found that very pure tungsten formed filaments that sagged in use, and that a very small "doping" treatment with potassium, silicon, and aluminium oxides at the level of a few hundred parts per million (so-called AKS tungsten) greatly improved the life and durability of the tungsten filaments.
The predominant mechanism for failure in tungsten filaments even now is grain boundary sliding accommodated by diffusional creep. During operation, the tungsten wire is stressed under the load of its own weight and because of the diffusion that can occur at high temperatures, grains begin to rotate and slide. This stress, because of variations in the filament, causes the filament to sag nonuniformly, which ultimately introduces further torque on the filament. It is this sagging that inevitably results in a rupture of the filament, rendering the incandescent lightbulb useless.
Coiled coil filament
To improve the efficiency of the lamp, the filament usually consists of multiple coils of coiled fine wire, also known as a coiled coil. Light bulbs using coiled coil filaments are sometimes referred to as 'double-coil bulbs'. For a 60-watt 120-volt lamp, the uncoiled length of the tungsten filament is usually , and the filament diameter is . The advantage of the coiled coil is that evaporation of the tungsten filament is at the rate of a tungsten cylinder having a diameter equal to that of the coiled coil. The coiled-coil filament evaporates more slowly than a straight filament of the same surface area and light-emitting power. As a result, the filament can then run hotter, which results in a more efficient light source while lasting longer than a straight filament at the same temperature.
Manufacturers designate different forms of lamp filament with an alphanumeric code. | Incandescent light bulb | Wikipedia | 489 | 47139 | https://en.wikipedia.org/wiki/Incandescent%20light%20bulb | Technology | Electricity generation and distribution | null |
Electrical filaments are also used in hot cathodes of fluorescent lamps and vacuum tubes as a source of electrons or in vacuum tubes to heat an electron-emitting electrode. When used as a source of electrons, they may have a special coating that increases electron production.
Reducing filament evaporation
During ordinary operation, the tungsten of the filament evaporates; hotter, more-efficient filaments evaporate faster. Because of this, the lifetime of a filament lamp is a trade-off between efficiency and longevity. The trade-off is typically set to provide a lifetime of 1,000 to 2,000 hours for lamps used for general illumination. Theatrical, photographic, and projection lamps may have a useful life of only a few hours, trading life expectancy for high output in a compact form. Long-life general service lamps have lower efficiency, but prior to the development of compact fluorescent and LED lamps they were useful in applications where the bulb was difficult to change.
Irving Langmuir found that an inert gas, instead of vacuum, would retard evaporation. General service incandescent light bulbs over about 25 watts in rating are now filled with a mixture of mostly argon and some nitrogen, or sometimes krypton. While inert gas reduces filament evaporation, it also conducts heat from the filament, thereby cooling the filament and reducing efficiency. At constant pressure and temperature, the thermal conductivity of a gas depends upon the molecular weight of the gas and the cross sectional area of the gas molecules. Higher molecular weight gases have lower thermal conductivity, because both the molecular weight and cross sectional area are higher. Xenon gas improves efficiency because of its high molecular weight, but is also more expensive, so its use is limited to smaller lamps. | Incandescent light bulb | Wikipedia | 373 | 47139 | https://en.wikipedia.org/wiki/Incandescent%20light%20bulb | Technology | Electricity generation and distribution | null |
Filament notching is due to uneven evaporation of the filament. Small variations in resistivity along the filament cause "hot spots" to form at points of higher resistivity; a variation of diameter of only 1% will cause a 25% reduction in service life. Since filament resistance is highly temperature-dependent, spots with higher temperature will have higher resistance, causing them to dissipate more energy, making them hotter – a positive feedback loop. These hot spots evaporate faster than the rest of the filament, permanently increasing the resistance at that point. The process ends in the familiar tiny gap in an otherwise healthy-looking filament.
Lamps operated on direct current develop random stairstep irregularities on the filament surface which may cut lifespan in half compared to AC operation; different alloys of tungsten and rhenium can be used to counteract the effect.
Since a filament breaking in a gas-filled bulb can form an electric arc, which may spread between the terminals and draw very heavy current, intentionally thin lead-in wires or more elaborate protection devices are therefore often used as fuses built into the light bulb. More nitrogen is used in higher-voltage lamps to reduce the possibility of arcing.
Bulb blackening
In a conventional lamp, the evaporated tungsten eventually condenses on the inner surface of the glass envelope, darkening it. For bulbs that contain a vacuum, the darkening is uniform across the entire surface of the envelope. When a filling of inert gas is used, the evaporated tungsten is carried in the thermal convection currents of the gas, and is deposited preferentially on the uppermost part of the envelope, blackening just that portion of the envelope. An incandescent lamp that gives 93% or less of its initial light output at 75% of its rated life is regarded as unsatisfactory, when tested according to IEC Publication 60064. Light loss is due to filament evaporation and bulb blackening. Study of the problem of bulb blackening led to the discovery of thermionic emission, the invention of the vacuum tube, and evaporation deposition used to make mirrors and other optical coatings. | Incandescent light bulb | Wikipedia | 453 | 47139 | https://en.wikipedia.org/wiki/Incandescent%20light%20bulb | Technology | Electricity generation and distribution | null |
A very small amount of water vapor inside a light bulb can significantly increase lamp darkening. Water vapor dissociates into hydrogen and oxygen at the hot filament. The oxygen attacks the tungsten metal, and the resulting tungsten oxide particles travel to cooler parts of the lamp. Hydrogen from water vapor reduces the oxide, reforming water vapor and continuing this water cycle. The equivalent of a drop of water distributed over 500,000 lamps will significantly increase darkening. Small amounts of substances such as zirconium are placed within the lamp as a getter to react with any oxygen that may bake out of the lamp components during operation.
Some old, high-powered lamps used in theater, projection, searchlight, and lighthouse service with heavy, sturdy filaments contained loose tungsten powder within the envelope. From time to time, the operator would remove the bulb and shake it, allowing the tungsten powder to scrub off most of the tungsten that had condensed on the interior of the envelope, removing the blackening and brightening the lamp again.
Halogen lamps
The halogen lamp reduces uneven evaporation of the filament and eliminates darkening of the envelope by filling the lamp with a halogen gas at low pressure, along with an inert gas. The halogen cycle increases the lifetime of the bulb and prevents its darkening by redepositing tungsten from the inside of the bulb back onto the filament. The halogen lamp can operate its filament at a higher temperature than a standard gas filled lamp of similar power without loss of operating life. Such bulbs are much smaller than normal incandescent bulbs, and are widely used where intense illumination is needed in a limited space. Fiber-optic lamps for optical microscopy is one typical application.
Incandescent arc lamps
A variation of the incandescent lamp did not use a hot wire filament, but instead used an arc struck on a spherical bead electrode to produce heat. The electrode then became incandescent, with the arc contributing little to the light produced. Such lamps were used for projection or illumination for scientific instruments such as microscopes. These arc lamps ran on relatively low voltages and incorporated tungsten filaments to start ionization within the envelope. They provided the intense concentrated light of an arc lamp but were easier to operate. Developed around 1915, these lamps were displaced by mercury and xenon arc lamps.
Electrical characteristics | Incandescent light bulb | Wikipedia | 489 | 47139 | https://en.wikipedia.org/wiki/Incandescent%20light%20bulb | Technology | Electricity generation and distribution | null |
Power
Incandescent lamps are nearly pure resistive loads with a power factor of 1. Unlike discharge lamps or LED lamps, the power consumed is equal to the apparent power in the circuit. Incandescent light bulbs are usually marketed according to the electrical power consumed. This depends mainly on the operating resistance of the filament. For two bulbs of the same voltage, and type, the higher-powered bulb gives more light.
The table shows the approximate typical output, in lumens, of standard 120 volt incandescent light bulbs at various powers. Light output of similar 230 V bulbs is slightly less. The lower current (higher voltage) filament is thinner and has to be operated at a slightly lower temperature for the same life expectancy, which reduces energy efficiency. The lumen values for "soft white" bulbs will generally be slightly lower than for clear bulbs at the same power.
Current and resistance
The resistance of the filament is temperature dependent. The cold resistance of tungsten-filament lamps is about the resistance when operating. For example, a 100-watt, 120-volt lamp has a resistance of 144 ohms when lit, but the cold resistance is much lower (about 9.5 ohms). Since incandescent lamps are resistive loads, simple phase-control TRIAC dimmers can be used to control brightness. Electrical contacts may carry a "T" rating symbol indicating that they are designed to control circuits with the high inrush current characteristic of tungsten lamps. For a 100-watt, 120-volt general-service lamp, the current stabilizes in about 0.10 seconds, and the lamp reaches 90% of its full brightness after about 0.13 seconds.
Physical characteristics
Safety
The filament in a tungsten light bulb is not easy to break when the bulb is cold, but filaments are more vulnerable when they are hot because the incandescent metal is less rigid. An impact on the outside of the bulb may cause the filament to break or experience a surge in electric current that causes part of it to melt or vaporize.
In most modern incandescent bulbs, part of the wire inside the bulb acts like a fuse: if a broken filament produces an electrical short inside the bulb, the fusible section of wire will melt and cut the current off to prevent damage to the supply lines. | Incandescent light bulb | Wikipedia | 486 | 47139 | https://en.wikipedia.org/wiki/Incandescent%20light%20bulb | Technology | Electricity generation and distribution | null |
A hot glass bulb may fracture on contact with cold objects. When the glass envelope breaks, the bulb implodes, exposing the filament to ambient air. The air then usually destroys the hot filament through oxidation.
Bulb shapes
Bulb shape and size designations are given in national standards.
Some designations are one or more letters followed by one or more numbers, e.g. A55 or PAR38, where the letters identify the shape and the numbers some characteristic size.
National standards such as ANSI C79.1-2002, IS 14897:2000 and JIS C 7710:1988 cover a common terminology for bulb shapes.
Common shape codes
General Service/General Lighting Service (GLS)
Light emitted in (nearly) all directions. Available either clear or frosted.
Types: General (A), elliptical (E), mushroom (M), sign (S), tubular (T)
120 V sizes: A17, 19 and 21
230 V sizes: A55 and 60
High Wattage General Service
Lamps greater than 200 watts.
Types: Pear-shaped (PS)
Decorative
lamps used in chandeliers, etc. Smaller candle-sized bulbs may use a smaller socket.
Types: candle (B), twisted candle, bent-tip candle (CA & BA), flame (F), globe (G), lantern chimney (H), fancy round (P)
230 V sizes: P45, G95
Reflector (R) Reflective coating inside the bulb directs light forward. Flood types (FL) spread light. Spot types (SP) concentrate the light. Reflector (R) bulbs put approximately double the amount of light (foot-candles) on the front central area as General Service (A) of same wattage.
Types: Standard reflector (R), bulged reflector (BR), elliptical reflector (ER), crown-silvered
120 V sizes: R16, 20, 25 and 30
230 V sizes: R50, 63, 80 and 95 | Incandescent light bulb | Wikipedia | 413 | 47139 | https://en.wikipedia.org/wiki/Incandescent%20light%20bulb | Technology | Electricity generation and distribution | null |
Parabolic aluminized reflector (PAR)
Parabolic aluminized reflector (PAR) bulbs control light more precisely. They produce about four times the concentrated light intensity of general service (A), and are used in recessed and track lighting. Weatherproof casings are available for outdoor spot and flood fixtures.
120 V sizes: PAR 16, 20, 30, 38, 56 and 64
230 V sizes: PAR 16, 20, 30, 38, 56 and 64
Available in numerous spot and flood beam spreads. Like all light bulbs, the number represents the diameter of the bulb in of an inch. Therefore, a PAR 16 is in diameter, a PAR 20 is in diameter, PAR 30 is and a PAR 38 is in diameter.
Multifaceted reflector (MR)
Multifaceted reflector bulbs are usually smaller in size and run at a lower voltage, often 12 V.
HIR/IRC "HIR" is a GE designation for a lamp with an infrared reflective coating. Since less heat escapes, the filament burns hotter and more efficiently. The Osram designation for a similar coating is "IRC".
Lamp bases
Large lamps may have a screw base or a bayonet base, with one or more contacts on the base. The shell may serve as an electrical contact or only as a mechanical support. Bayonet base lamps are frequently used in automotive lamps to resist loosening by vibration. Some tubular lamps have an electrical contact at either end. Miniature lamps may have a wedge base and wire contacts, and some automotive and special purpose lamps have screw terminals for connection to wires. Very small lamps may have the filament support wires extended through the base of the lamp for connections. A bipin base is often used for halogen or reflector lamps.
In the late 19th century, manufacturers introduced a multitude of incompatible lamp bases. General Electric's "Mazda" standard base sizes were soon adopted across the US.
Lamp bases may be secured to the bulb with a cement, or by mechanical crimping to indentations molded into the glass bulb.
Lamps intended for use in optical systems have bases with alignment features so that the filament is positioned accurately within the optical system. A screw-base lamp may have a random orientation of the filament when the lamp is installed in the socket. | Incandescent light bulb | Wikipedia | 475 | 47139 | https://en.wikipedia.org/wiki/Incandescent%20light%20bulb | Technology | Electricity generation and distribution | null |
Contacts in the lightbulb socket allow the electric current to pass through the base to the filament. The socket provides electrical connections and mechanical support, and allows changing the lamp when it burns out.
Light output and lifetime
Incandescent lamps are very sensitive to changes in the supply voltage. These characteristics are of great practical and economic importance.
For a supply voltage V near the rated voltage of the lamp:
Light output is approximately proportional to V 3.4
Power consumption is approximately proportional to V 1.6
Lifetime is approximately proportional to V −16
Color temperature is approximately proportional to V 0.42
A 5% reduction in voltage will double the life of the bulb, but reduce its light output by about 16%. Long-life bulbs take advantage of this trade-off in applications such as traffic signal lamps. Since electric energy they use costs more than the cost of the bulb, general service lamps emphasize efficiency over long operating life. The objective is to minimize the cost of light, not the cost of lamps. Early bulbs had a life of up to 2500 hours, but in 1924 the Phoebus cartel agreed to limit life to 1000 hours. When this was exposed in 1953, General Electric and other leading American manufacturers were banned from limiting the life.
The relationships above are valid for only a few percent change of voltage around standard rated conditions, but they indicate that a lamp operated at low voltage could last much longer than at rated voltage, albeit with greatly reduced light output. The "Centennial Light" is a light bulb that is accepted by the Guinness Book of World Records as having been burning almost continuously at a fire station in Livermore, California, since 1901. However, the bulb emits the equivalent light of a four watt bulb. A similar story can be told of a 40-watt bulb in Texas that has been illuminated since 21 September 1908. It once resided in an opera house where notable celebrities stopped to take in its glow, and was moved to an area museum in 1977.
Photoflood lamps used for photographic lighting favor light output over life, with some lasting only two hours. The upper temperature limit for the filament is the melting point of the metal. Tungsten is the metal with the highest melting point, . A 50-hour-life projection bulb, for instance, is designed to operate only below that melting point. Such a lamp may achieve up to 22 lumens per watt, compared with 17.5 for a 750-hour general service lamp. | Incandescent light bulb | Wikipedia | 498 | 47139 | https://en.wikipedia.org/wiki/Incandescent%20light%20bulb | Technology | Electricity generation and distribution | null |
Lamps of the same power rating but designed for different voltages have different luminous efficacy. For example, a 100-watt, 1000 hour, 120-volt lamp will produce about 17.1 lumens per watt. A similar lamp designed for 230 V would produce only around 12.8 lumens per watt, and one designed for 30 volts (train lighting) would produce as much as 19.8 lumens per watt. Lower voltage lamps have a thicker filament, for the same power rating. They can run hotter for the same lifetime before the filament evaporates.
The wires used to support the filament make it mechanically stronger, but remove heat, creating another tradeoff between efficiency and long life. Many general-service 120-volt lamps use no additional support wires, but lamps designed for "rough service" or "vibration service" may have as many as five. Low-voltage lamps have filaments made of heavier wire and do not require additional support wires.
Very low voltages are inefficient since the lead wires would conduct too much heat away from the filament, so the practical lower limit for incandescent lamps is 1.5 volts. Very long filaments for high voltages are fragile, and lamp bases become more difficult to insulate, so lamps for illumination are not made with rated voltages over 300 volts. Some infrared heating elements are made for higher voltages, but these use tubular bulbs with widely separated terminals. | Incandescent light bulb | Wikipedia | 308 | 47139 | https://en.wikipedia.org/wiki/Incandescent%20light%20bulb | Technology | Electricity generation and distribution | null |
Vesta (minor-planet designation: 4 Vesta) is one of the largest objects in the asteroid belt, with a mean diameter of . It was discovered by the German astronomer Heinrich Wilhelm Matthias Olbers on 29 March 1807 and is named after Vesta, the virgin goddess of home and hearth from Roman mythology.
Vesta is thought to be the second-largest asteroid, both by mass and by volume, after the dwarf planet Ceres. Measurements give it a nominal volume only slightly larger than that of Pallas (about 5% greater), but it is 25% to 30% more massive. It constitutes an estimated 9% of the mass of the asteroid belt. Vesta is the only known remaining rocky protoplanet (with a differentiated interior) of the kind that formed the terrestrial planets. Numerous fragments of Vesta were ejected by collisions one and two billion years ago that left two enormous craters occupying much of Vesta's southern hemisphere. Debris from these events has fallen to Earth as howardite–eucrite–diogenite (HED) meteorites, which have been a rich source of information about Vesta.
Vesta is the brightest asteroid visible from Earth. It is regularly as bright as magnitude 5.1, at which times it is faintly visible to the naked eye. Its maximum distance from the Sun is slightly greater than the minimum distance of Ceres from the Sun, although its orbit lies entirely within that of Ceres.
NASA's Dawn spacecraft entered orbit around Vesta on 16 July 2011 for a one-year exploration and left the orbit of Vesta on 5 September 2012 en route to its final destination, Ceres. Researchers continue to examine data collected by Dawn for additional insights into the formation and history of Vesta.
History
Discovery | 4 Vesta | Wikipedia | 356 | 47200 | https://en.wikipedia.org/wiki/4%20Vesta | Physical sciences | Solar System | Astronomy |
Heinrich Olbers discovered Pallas in 1802, the year after the discovery of Ceres. He proposed that the two objects were the remnants of a destroyed planet. He sent a letter with his proposal to the British astronomer William Herschel, suggesting that a search near the locations where the orbits of Ceres and Pallas intersected might reveal more fragments. These orbital intersections were located in the constellations of Cetus and Virgo. Olbers commenced his search in 1802, and on 29 March 1807 he discovered Vesta in the constellation Virgo—a coincidence, because Ceres, Pallas, and Vesta are not fragments of a larger body. Because the asteroid Juno had been discovered in 1804, this made Vesta the fourth object to be identified in the region that is now known as the asteroid belt. The discovery was announced in a letter addressed to German astronomer Johann H. Schröter dated 31 March. Because Olbers already had credit for discovering a planet (Pallas; at the time, the asteroids were considered to be planets), he gave the honor of naming his new discovery to German mathematician Carl Friedrich Gauss, whose orbital calculations had enabled astronomers to confirm the existence of Ceres, the first asteroid, and who had computed the orbit of the new planet in the remarkably short time of 10 hours. Gauss decided on the Roman virgin goddess of home and hearth, Vesta.
Name and symbol
Vesta was the fourth asteroid to be discovered, hence the number 4 in its formal designation. The name Vesta, or national variants thereof, is in international use with two exceptions: Greece and China. In Greek, the name adopted was the Hellenic equivalent of Vesta, Hestia in English, that name is used for (Greeks use the name "Hestia" for both, with the minor-planet numbers used for disambiguation). In Chinese, Vesta is called the 'hearth-god(dess) star', , naming the asteroid for Vesta's role, similar to the Chinese names of Uranus, Neptune, and Pluto. | 4 Vesta | Wikipedia | 422 | 47200 | https://en.wikipedia.org/wiki/4%20Vesta | Physical sciences | Solar System | Astronomy |
Upon its discovery, Vesta was, like Ceres, Pallas, and Juno before it, classified as a planet and given a planetary symbol. The symbol represented the altar of Vesta with its sacred fire and was designed by Gauss. In Gauss's conception, now obsolete, this was drawn . His form is in the pipeline for Unicode 17.0 as U+1F777 .
The asteroid symbols were gradually retired from astronomical use after 1852, but the symbols for the first four asteroids were resurrected for astrology in the 1970s. The abbreviated modern astrological variant of the Vesta symbol is .
After the discovery of Vesta, no further objects were discovered for 38 years, and during this time the Solar System was thought to have eleven planets. However, in 1845, new asteroids started being discovered at a rapid pace, and by 1851 there were fifteen, each with its own symbol, in addition to the eight major planets (Neptune had been discovered in 1846). It soon became clear that it would be impractical to continue inventing new planetary symbols indefinitely, and some of the existing ones proved difficult to draw quickly. That year, the problem was addressed by Benjamin Apthorp Gould, who suggested numbering asteroids in their order of discovery, and placing this number in a disk (circle) as the generic symbol of an asteroid. Thus, the fourth asteroid, Vesta, acquired the generic symbol . This was soon coupled with the name into an official number–name designation, as the number of minor planets increased. By 1858, the circle had been simplified to parentheses, which were easier to typeset. Other punctuation, such as and was also briefly used, but had more or less completely died out by 1949.
Early measurements
Photometric observations of Vesta were made at the Harvard College Observatory in 1880–1882 and at the Observatoire de Toulouse in 1909. These and other observations allowed the rotation rate of Vesta to be determined by the 1950s. However, the early estimates of the rotation rate came into question because the light curve included variations in both shape and albedo. | 4 Vesta | Wikipedia | 426 | 47200 | https://en.wikipedia.org/wiki/4%20Vesta | Physical sciences | Solar System | Astronomy |
Early estimates of the diameter of Vesta ranged from in 1825, to . E.C. Pickering produced an estimated diameter of in 1879, which is close to the modern value for the mean diameter, but the subsequent estimates ranged from a low of up to a high of during the next century. The measured estimates were based on photometry. In 1989, speckle interferometry was used to measure a dimension that varied between during the rotational period. In 1991, an occultation of the star SAO 93228 by Vesta was observed from multiple locations in the eastern United States and Canada. Based on observations from 14 different sites, the best fit to the data was an elliptical profile with dimensions of about . Dawn confirmed this measurement. These measurements will help determine the thermal history, size of the core, role of water in asteroid evolution and what meteorites found on Earth come from these bodies, with the ultimate goal of understanding the conditions and processes present at the solar system's earliest epoch and the role of water content and size in planetary evolution.
Vesta became the first asteroid to have its mass determined. Every 18 years, the asteroid 197 Arete approaches within of Vesta. In 1966, based upon observations of Vesta's gravitational perturbations of Arete, Hans G. Hertz estimated the mass of Vesta at (solar masses). More refined estimates followed, and in 2001 the perturbations of 17 Thetis were used to calculate the mass of Vesta to be . Dawn determined it to be .
Orbit
Vesta orbits the Sun between Mars and Jupiter, within the asteroid belt, with a period of 3.6 Earth years, specifically in the inner asteroid belt, interior to the Kirkwood gap at 2.50 AU. Its orbit is moderately inclined (i = 7.1°, compared to 7° for Mercury and 17° for Pluto) and moderately eccentric (e = 0.09, about the same as for Mars).
True orbital resonances between asteroids are considered unlikely. Because of their small masses relative to their large separations, such relationships should be very rare. Nevertheless, Vesta is able to capture other asteroids into temporary 1:1 resonant orbital relationships (for periods up to 2 million years or more) and about forty such objects have been identified. Decameter-sized objects detected in the vicinity of Vesta by Dawn may be such quasi-satellites rather than proper satellites.
Rotation | 4 Vesta | Wikipedia | 494 | 47200 | https://en.wikipedia.org/wiki/4%20Vesta | Physical sciences | Solar System | Astronomy |
Vesta's rotation is relatively fast for an asteroid (5.342 h) and prograde, with the north pole pointing in the direction of right ascension 20 h 32 min, declination +48° (in the constellation Cygnus) with an uncertainty of about 10°. This gives an axial tilt of 29°.
Coordinate systems
Two longitudinal coordinate systems are used for Vesta, with prime meridians separated by 150°. The IAU established a coordinate system in 1997 based on Hubble photos, with the prime meridian running through the center of Olbers Regio, a dark feature 200 km across. When Dawn arrived at Vesta, mission scientists found that the location of the pole assumed by the IAU was off by 10°, so that the IAU coordinate system drifted across the surface of Vesta at 0.06° per year, and also that Olbers Regio was not discernible from up close, and so was not adequate to define the prime meridian with the precision they needed. They corrected the pole, but also established a new prime meridian 4° from the center of Claudia, a sharply defined crater 700 meters across, which they say results in a more logical set of mapping quadrangles. All NASA publications, including images and maps of Vesta, use the Claudian meridian, which is unacceptable to the IAU. The IAU Working Group on Cartographic Coordinates and Rotational Elements recommended a coordinate system, correcting the pole but rotating the Claudian longitude by 150° to coincide with Olbers Regio. It was accepted by the IAU, although it disrupts the maps prepared by the Dawn team, which had been positioned so they would not bisect any major surface features.
Physical characteristics
Vesta is the second most massive body in the asteroid belt, although it is only 28% as massive as Ceres, the most massive body. Vesta is however the most massive body that formed in the asteroid belt, as Ceres is believed to have formed between Jupiter and Saturn. Vesta's density is lower than those of the four terrestrial planets but is higher than those of most asteroids, as well as all of the moons in the Solar System except Io. Vesta's surface area is about the same as the land area of Pakistan, Venezuela, Tanzania, or Nigeria; slightly under . It has a differentiated interior. Vesta is only slightly larger () than 2 Pallas () in mean diameter, but is about 25% more massive. | 4 Vesta | Wikipedia | 505 | 47200 | https://en.wikipedia.org/wiki/4%20Vesta | Physical sciences | Solar System | Astronomy |
Vesta's shape is close to a gravitationally relaxed oblate spheroid, but the large concavity and protrusion at the southern pole (see 'Surface features' below) combined with a mass less than precluded Vesta from automatically being considered a dwarf planet under International Astronomical Union (IAU) Resolution XXVI 5. A 2012 analysis of Vesta's shape and gravity field using data gathered by the Dawn spacecraft has shown that Vesta is currently not in hydrostatic equilibrium.
Temperatures on the surface have been estimated to lie between about with the Sun overhead, dropping to about at the winter pole. Typical daytime and nighttime temperatures are and , respectively. This estimate is for 6 May 1996, very close to perihelion, although details vary somewhat with the seasons.
Surface features
Before the arrival of the Dawn spacecraft, some Vestan surface features had already been resolved using the Hubble Space Telescope and ground-based telescopes (e.g., the Keck Observatory). The arrival of Dawn in July 2011 revealed the complex surface of Vesta in detail.
Rheasilvia and Veneneia | 4 Vesta | Wikipedia | 227 | 47200 | https://en.wikipedia.org/wiki/4%20Vesta | Physical sciences | Solar System | Astronomy |
The most prominent of these surface features are two enormous impact basins, the -wide Rheasilvia, centered near the south pole; and the wide Veneneia. The Rheasilvia impact basin is younger and overlies the Veneneia. The Dawn science team named the younger, more prominent crater Rheasilvia, after the mother of Romulus and Remus and a mythical vestal virgin. Its width is 95% of the mean diameter of Vesta. The crater is about deep. A central peak rises above the lowest measured part of the crater floor and the highest measured part of the crater rim is above the crater floor low point. It is estimated that the impact responsible excavated about 1% of the volume of Vesta, and it is likely that the Vesta family and V-type asteroids are the products of this collision. If this is the case, then the fact that fragments have survived bombardment until the present indicates that the crater is at most only about 1 billion years old. It would also be the site of origin of the HED meteorites. All the known V-type asteroids taken together account for only about 6% of the ejected volume, with the rest presumably either in small fragments, ejected by approaching the 3:1 Kirkwood gap, or perturbed away by the Yarkovsky effect or radiation pressure. Spectroscopic analyses of the Hubble images have shown that this crater has penetrated deep through several distinct layers of the crust, and possibly into the mantle, as indicated by spectral signatures of olivine.
The large peak at the center of Rheasilvia is high and wide, and is possibly a result of a planetary-scale impact.
Other craters
Several old, degraded craters approach Rheasilvia and Veneneia in size, although none are quite so large. They include Feralia Planitia, shown at right, which is across. More-recent, sharper craters range up to Varronilla and Postumia.
Dust fills up some craters, creating so-called dust ponds. They are a phenomenon where pockets of dust are seen in celestial bodies without a significant atmosphere. These are smooth deposits of dust accumulated in depressions on the surface of the body (like craters), contrasting from the Rocky terrain around them. On the surface of Vesta, we have identified both type 1 (formed from impact melt) and type 2 (electrostatically made) dust ponds within 0˚–30°N/S, that is, Equatorial region. 10 craters have been identified with such formations. | 4 Vesta | Wikipedia | 509 | 47200 | https://en.wikipedia.org/wiki/4%20Vesta | Physical sciences | Solar System | Astronomy |
"Snowman craters"
The "snowman craters" are a group of three adjacent craters in Vesta's northern hemisphere. Their official names, from largest to smallest (west to east), are Marcia, Calpurnia, and Minucia. Marcia is the youngest and cross-cuts Calpurnia. Minucia is the oldest.
Troughs
The majority of the equatorial region of Vesta is sculpted by a series of parallel troughs designated Divalia Fossae; its longest trough is wide and long. Despite the fact that Vesta is a one-seventh the size of the Moon, Divalia Fossae dwarfs the Grand Canyon. A second series, inclined to the equator, is found further north. This northern trough system is named Saturnalia Fossae, with its largest trough being roughly 40 km wide and over 370 km long. These troughs are thought to be large-scale graben resulting from the impacts that created Rheasilvia and Veneneia craters, respectively. They are some of the longest chasms in the Solar System, nearly as long as Ithaca Chasma on Tethys. The troughs may be graben that formed after another asteroid collided with Vesta, a process that can happen only in a body that, like Vesta, is differentiated. Vesta's differentiation is one of the reasons why scientists consider it a protoplanet. Alternatively, it is proposed that the troughs may be radial sculptures created by secondary cratering from Rheasilvia. | 4 Vesta | Wikipedia | 305 | 47200 | https://en.wikipedia.org/wiki/4%20Vesta | Physical sciences | Solar System | Astronomy |
Surface composition
Compositional information from the visible and infrared spectrometer (VIR), gamma-ray and neutron detector (GRaND), and framing camera (FC), all indicate that the majority of the surface composition of Vesta is consistent with the composition of the howardite, eucrite, and diogenite meteorites. The Rheasilvia region is richest in diogenite, consistent with the Rheasilvia-forming impact excavating material from deeper within Vesta. The presence of olivine within the Rheasilvia region would also be consistent with excavation of mantle material. However, olivine has only been detected in localized regions of the northern hemisphere, not within Rheasilvia. The origin of this olivine is currently unclear. Though olivine was expected by astronomers to have originated from Vesta's mantle prior to the arrival of the Dawn orbiter, the lack of olivine within the Rheasilvia and Veneneia impact basins complicates this view. Both impact basins excavated Vestian material down to 60–100 km, far deeper than the expected thickness of ~30–40 km for Vesta's crust. Vesta's crust may be far thicker than expected or the violent impact events that created Rheasilvia and Veneneia may have mixed material enough to obscure olivine from observations. Alternatively, Dawn observations of olivine could instead be due to delivery by olivine-rich impactors, unrelated to Vesta's internal structure.
Features associated with volatiles
Pitted terrain has been observed in four craters on Vesta: Marcia, Cornelia, Numisia and Licinia. The formation of the pitted terrain is proposed to be degassing of impact-heated volatile-bearing material. Along with the pitted terrain, curvilinear gullies are found in Marcia and Cornelia craters. The curvilinear gullies end in lobate deposits, which are sometimes covered by pitted terrain, and are proposed to form by the transient flow of liquid water after buried deposits of ice were melted by the heat of the impacts. Hydrated materials have also been detected, many of which are associated with areas of dark material. Consequently, dark material is thought to be largely composed of carbonaceous chondrite, which was deposited on the surface by impacts. Carbonaceous chondrites are comparatively rich in mineralogically bound OH.
Geology | 4 Vesta | Wikipedia | 494 | 47200 | https://en.wikipedia.org/wiki/4%20Vesta | Physical sciences | Solar System | Astronomy |
A large collection of potential samples from Vesta is accessible to scientists, in the form of over 1200 HED meteorites (Vestan achondrites), giving insight into Vesta's geologic history and structure. NASA Infrared Telescope Facility (NASA IRTF) studies of asteroid suggest that it originated from deeper within Vesta than the HED meteorites.
Vesta is thought to consist of a metallic iron–nickel core 214–226 km in diameter, an overlying rocky olivine mantle, with a surface crust. From the first appearance of calcium–aluminium-rich inclusions (the first solid matter in the Solar System, forming about 4.567 billion years ago), a likely time line is as follows:
Vesta is the only known intact asteroid that has been resurfaced in this manner. Because of this, some scientists refer to Vesta as a protoplanet. However, the presence of iron meteorites and achondritic meteorite classes without identified parent bodies indicates that there once were other differentiated planetesimals with igneous histories, which have since been shattered by impacts.
On the basis of the sizes of V-type asteroids (thought to be pieces of Vesta's crust ejected during large impacts), and the depth of Rheasilvia crater (see below), the crust is thought to be roughly thick.
Findings from the Dawn spacecraft have found evidence that the troughs that wrap around Vesta could be graben formed by impact-induced faulting (see Troughs section above), meaning that Vesta has more complex geology than other asteroids. Vesta's differentiated interior implies that it was in hydrostatic equilibrium and thus a dwarf planet in the past, but it is not today. The impacts that created the Rheasilvia and Veneneia craters occurred when Vesta was no longer warm and plastic enough to return to an equilibrium shape, distorting its once rounded shape and prohibiting it from being classified as a dwarf planet today. | 4 Vesta | Wikipedia | 404 | 47200 | https://en.wikipedia.org/wiki/4%20Vesta | Physical sciences | Solar System | Astronomy |
Regolith
Vesta's surface is covered by regolith distinct from that found on the Moon or asteroids such as Itokawa. This is because space weathering acts differently. Vesta's surface shows no significant trace of nanophase iron because the impact speeds on Vesta are too low to make rock melting and vaporization an appreciable process. Instead, regolith evolution is dominated by brecciation and subsequent mixing of bright and dark components. The dark component is probably due to the infall of carbonaceous material, whereas the bright component is the original Vesta basaltic soil.
Fragments
Some small Solar System bodies are suspected to be fragments of Vesta caused by impacts. The Vestian asteroids and HED meteorites are examples. The V-type asteroid 1929 Kollaa has been determined to have a composition akin to cumulate eucrite meteorites, indicating its origin deep within Vesta's crust.
Vesta is currently one of only eight identified Solar System bodies of which we have physical samples, coming from a number of meteorites suspected to be Vestan fragments. It is estimated that 1 out of 16 meteorites originated from Vesta. The other identified Solar System samples are from Earth itself, meteorites from Mars, meteorites from the Moon, and samples returned from the Moon, the comet Wild 2, and the asteroids 25143 Itokawa, 162173 Ryugu, and 101955 Bennu.
Exploration | 4 Vesta | Wikipedia | 295 | 47200 | https://en.wikipedia.org/wiki/4%20Vesta | Physical sciences | Solar System | Astronomy |
In 1981, a proposal for an asteroid mission was submitted to the European Space Agency (ESA). Named the Asteroidal Gravity Optical and Radar Analysis (AGORA), this spacecraft was to launch some time in 1990–1994 and perform two flybys of large asteroids. The preferred target for this mission was Vesta. AGORA would reach the asteroid belt either by a gravitational slingshot trajectory past Mars or by means of a small ion engine. However, the proposal was refused by the ESA. A joint NASA–ESA asteroid mission was then drawn up for a Multiple Asteroid Orbiter with Solar Electric Propulsion (MAOSEP), with one of the mission profiles including an orbit of Vesta. NASA indicated they were not interested in an asteroid mission. Instead, the ESA set up a technological study of a spacecraft with an ion drive. Other missions to the asteroid belt were proposed in the 1980s by France, Germany, Italy and the United States, but none were approved. Exploration of Vesta by fly-by and impacting penetrator was the second main target of the first plan of the multi-aimed Soviet Vesta mission, developed in cooperation with European countries for realisation in 1991–1994 but canceled due to the dissolution of the Soviet Union.
In the early 1990s, NASA initiated the Discovery Program, which was intended to be a series of low-cost scientific missions. In 1996, the program's study team recommended a mission to explore the asteroid belt using a spacecraft with an ion engine as a high priority. Funding for this program remained problematic for several years, but by 2004 the Dawn vehicle had passed its critical design review and construction proceeded.
It launched on 27 September 2007 as the first space mission to Vesta. On 3 May 2011, Dawn acquired its first targeting image 1.2 million kilometers from Vesta. On 16 July 2011, NASA confirmed that it received telemetry from Dawn indicating that the spacecraft successfully entered Vesta's orbit. It was scheduled to orbit Vesta for one year, until July 2012. Dawn arrival coincided with late summer in the southern hemisphere of Vesta, with the large crater at Vesta's south pole (Rheasilvia) in sunlight. Because a season on Vesta lasts eleven months, the northern hemisphere, including anticipated compression fractures opposite the crater, would become visible to Dawn cameras before it left orbit. Dawn left orbit around Vesta on 4 September 2012 to travel to Ceres. | 4 Vesta | Wikipedia | 491 | 47200 | https://en.wikipedia.org/wiki/4%20Vesta | Physical sciences | Solar System | Astronomy |
NASA/DLR released imagery and summary information from a survey orbit, two high-altitude orbits (60–70 m/pixel) and a low-altitude mapping orbit (20 m/pixel), including digital terrain models, videos and atlases. Scientists also used Dawn to calculate Vesta's precise mass and gravity field. The subsequent determination of the J2 component yielded a core diameter estimate of about 220 km assuming a crustal density similar to that of the HED.
Dawn data can be accessed by the public at the UCLA website.
Observations from Earth orbit
Observations from Dawn
Vesta comes into view as the Dawn spacecraft approaches and enters orbit:
True-color images
Detailed images retrieved during the high-altitude (60–70 m/pixel) and low-altitude (~20 m/pixel) mapping orbits are available on the Dawn Mission website of JPL/NASA.
Visibility
Its size and unusually bright surface make Vesta the brightest asteroid, and it is occasionally visible to the naked eye from dark skies (without light pollution). In May and June 2007, Vesta reached a peak magnitude of +5.4, the brightest since 1989. At that time, opposition and perihelion were only a few weeks apart. It was brighter still at its 22 June 2018 opposition, reaching a magnitude of +5.3.
Less favorable oppositions during late autumn 2008 in the Northern Hemisphere still had Vesta at a magnitude of from +6.5 to +7.3. Even when in conjunction with the Sun, Vesta will have a magnitude around +8.5; thus from a pollution-free sky it can be observed with binoculars even at elongations much smaller than near opposition.
2010–2011
In 2010, Vesta reached opposition in the constellation of Leo on the night of 17–18 February, at about magnitude 6.1, a brightness that makes it visible in binocular range but generally not for the naked eye. Under perfect dark sky conditions where all light pollution is absent it might be visible to an experienced observer without the use of a telescope or binoculars. Vesta came to opposition again on 5 August 2011, in the constellation of Capricornus at about magnitude 5.6. | 4 Vesta | Wikipedia | 448 | 47200 | https://en.wikipedia.org/wiki/4%20Vesta | Physical sciences | Solar System | Astronomy |
2012–2013
Vesta was at opposition again on 9 December 2012. According to Sky and Telescope magazine, this year Vesta came within about 6 degrees of 1 Ceres during the winter of 2012 and spring 2013. Vesta orbits the Sun in 3.63 years and Ceres in 4.6 years, so every 17.4 years Vesta overtakes Ceres (the previous overtaking was in April 1996). On 1 December 2012, Vesta had a magnitude of 6.6, but it had decreased to 8.4 by 1 May 2013.
2014
Ceres and Vesta came within one degree of each other in the night sky in July 2014. | 4 Vesta | Wikipedia | 135 | 47200 | https://en.wikipedia.org/wiki/4%20Vesta | Physical sciences | Solar System | Astronomy |
Pallas (minor-planet designation: 2 Pallas) is the third-largest asteroid in the Solar System by volume and mass. It is the second asteroid to have been discovered, after Ceres, and is likely a remnant protoplanet. Like Ceres, it is believed to have a mineral composition similar to carbonaceous chondrite meteorites, though significantly less hydrated than Ceres. It is 79% the mass of Vesta and 22% the mass of Ceres, constituting an estimated 7% of the mass of the asteroid belt. Its estimated volume is equivalent to a sphere in diameter, 90–95% the volume of Vesta.
During the planetary formation era of the Solar System, objects grew in size through an accretion process to approximately the size of Pallas. Most of these protoplanets were incorporated into the growth of larger bodies, which became the planets, whereas others were ejected by the planets or destroyed in collisions with each other. Pallas, Vesta and Ceres appear to be the only intact bodies from this early stage of planetary formation to survive within the orbit of Neptune.
When Pallas was discovered by the German astronomer Heinrich Wilhelm Matthias Olbers on 28 March 1802, it was considered to be a planet, as were other asteroids in the early 19th century. The discovery of many more asteroids after 1845 eventually led to the separate listing of "minor" planets from "major" planets, and the realization in the 1950s that such small bodies did not form in the same way as (other) planets led to the gradual abandonment of the term "minor planet" in favor of "asteroid" (or, for larger bodies such as Pallas, "planetoid").
With an orbital inclination of 34.8°, Pallas's orbit is unusually highly inclined to the plane of the asteroid belt, making Pallas relatively inaccessible to spacecraft, and its orbital eccentricity is nearly as large as that of Pluto.
The high inclination of the orbit of Pallas results in the possibility of close conjunctions to stars that other solar objects always pass at great angular distance. This resulted in Pallas passing Sirius on 9 October 2022, only 8.5 arcminutes southwards, while no planet can get closer than 30 degrees to Sirius.
History | 2 Pallas | Wikipedia | 462 | 47262 | https://en.wikipedia.org/wiki/2%20Pallas | Physical sciences | Solar System | Astronomy |
Discovery
On the night of 5 April 1779, Charles Messier recorded Pallas on a star chart he used to track the path of a comet, now known as C/1779 A1 (Bode), that he observed in the spring of 1779, but apparently assumed it was nothing more than a star.
In 1801, the astronomer Giuseppe Piazzi discovered an object which he initially believed to be a comet. Shortly thereafter he announced his observations of this object, noting that the slow, uniform motion was uncharacteristic of a comet, suggesting it was a different type of object. This was lost from sight for several months, but was recovered later that year by the Baron von Zach and Heinrich W. M. Olbers after a preliminary orbit was computed by Carl Friedrich Gauss. This object came to be named Ceres, and was the first asteroid to be discovered.
A few months later, Olbers was again attempting to locate Ceres when he noticed another moving object in the vicinity. This was the asteroid Pallas, coincidentally passing near Ceres at the time. The discovery of this object created interest in the astronomy community. Before this point it had been speculated by astronomers that there should be a planet in the gap between Mars and Jupiter. Now, unexpectedly, a second such body had been found. When Pallas was discovered, some estimates of its size were as high as 3,380 km in diameter. Even as recently as 1979, Pallas was estimated to be 673 km in diameter, 26% greater than the currently accepted value.
The orbit of Pallas was determined by Gauss, who found the period of 4.6 years was similar to the period for Ceres. Pallas has a relatively high orbital inclination to the plane of the ecliptic.
Later observations
In 1917, the Japanese astronomer Kiyotsugu Hirayama began to study asteroid motions. By plotting the mean orbital motion, inclination, and eccentricity of a set of asteroids, he discovered several distinct groupings. In a later paper he reported a group of three asteroids associated with Pallas, which became named the Pallas family, after the largest member of the group. Since 1994 more than 10 members of this family have been identified, with semi-major axes between 2.50 and 2.82 AU and inclinations of 33–38°. The validity of the family was confirmed in 2002 by a comparison of their spectra. | 2 Pallas | Wikipedia | 487 | 47262 | https://en.wikipedia.org/wiki/2%20Pallas | Physical sciences | Solar System | Astronomy |
Pallas has been observed occulting stars several times, including the best-observed of all asteroid occultation events, by 140 observers on 29 May 1983. These measurements resulted in the first accurate calculation of its diameter.
After an occultation on 29 May 1979, the discovery of a possible tiny satellite with a diameter of about 1 km was reported, which was never confirmed.
Radio signals from spacecraft in orbit around Mars and/or on its surface have been used to estimate the mass of Pallas from the tiny perturbations induced by it onto the motion of Mars.
The Dawn team was granted viewing time on the Hubble Space Telescope in September 2007 for a once-in-twenty-year opportunity to view Pallas at closest approach, to obtain comparative data for Ceres and Vesta.
Name and symbol
Pallas is an epithet of the Greek goddess Athena (). In some versions of the myth, Athena killed Pallas, daughter of Triton, then adopted her friend's name out of mourning.
The adjectival form of the name is Palladian. The d is part of the oblique stem of the Greek name, which appears before a vowel but disappears before the nominative ending -s. The oblique form is seen in the Italian and Russian names for the asteroid, and ().
The stony-iron pallasite meteorites are not Palladian, being named instead after the German naturalist Peter Simon Pallas. The chemical element palladium, on the other hand, was named after the asteroid, which had been discovered just before the element.
The old astronomical symbol of Pallas, still used in astrology, is a spear or lance, , one of the symbols of the goddess. The blade was most often a lozenge (), but various graphic variants were published, including an acute/elliptic leaf shape, a cordate leaf shape (: ), and a triangle (); the last made it effectively the alchemical symbol for sulfur, . The generic asteroid symbol of a disk with its discovery number, , was introduced in 1852 and quickly became the norm. The iconic lozenge symbol was resurrected for astrological use in 1973.
Orbit and rotation | 2 Pallas | Wikipedia | 444 | 47262 | https://en.wikipedia.org/wiki/2%20Pallas | Physical sciences | Solar System | Astronomy |
Pallas has unusual dynamic parameters for such a large body. Its orbit is highly inclined and moderately eccentric, despite being at the same distance from the Sun as the central part of the asteroid belt. Furthermore, Pallas has a very high axial tilt of 84°, with its north pole pointing towards ecliptic coordinates (β, λ) = (30°, −16°) with a 5° uncertainty in the Ecliptic J2000.0 reference frame. This means that every Palladian summer and winter, large parts of the surface are in constant sunlight or constant darkness for a time on the order of an Earth year, with areas near the poles experiencing continuous sunlight for as long as two years.
Near resonances
Pallas is in a near-1:1 orbital resonance with Ceres, which is probably coincidental. Pallas also has a near-18:7 resonance (91,000-year period) and an approximate 5:2 resonance (83-year period) with Jupiter.
Transits of planets from Pallas
From Pallas, the planets Mercury, Venus, Mars, and Earth can occasionally appear to transit, or pass in front of, the Sun. Earth last did so in 1968 and 1998, and will next transit in 2224. Mercury did in October 2009. The last and next by Venus are in 1677 and 2123, and for Mars they are in 1597 and 2759.
Physical characteristics
Both Vesta and Pallas have assumed the title of second-largest asteroid from time to time. At in diameter, Pallas is slightly smaller than Vesta (). The mass of Pallas is that of Vesta, that of Ceres, and a quarter of one percent that of the Moon.
Pallas is farther from Earth and has a much lower albedo than Vesta, and hence is dimmer as seen from Earth. Indeed, the much smaller asteroid 7 Iris marginally exceeds Pallas in mean opposition magnitude. Pallas's mean opposition magnitude is +8.0, which is well within the range of 10×50 binoculars, but, unlike Ceres and Vesta, it will require more-powerful optical aid to view at small elongations, when its magnitude can drop as low as +10.6. During rare perihelic oppositions, Pallas can reach a magnitude of +6.4, right on the edge of naked-eye visibility. During late February 2014 Pallas shone with magnitude 6.96. | 2 Pallas | Wikipedia | 505 | 47262 | https://en.wikipedia.org/wiki/2%20Pallas | Physical sciences | Solar System | Astronomy |
Pallas is a B-type asteroid. Based on spectroscopic observations, the primary component of the material on Pallas's surface is a silicate containing little iron and water. Minerals of this type include olivine and pyroxene, which are found in CM chondrules. The surface composition of Pallas is very similar to the Renazzo carbonaceous chondrite (CR) meteorites, which are even lower in hydrous minerals than the CM type. The Renazzo meteorite was discovered in Italy in 1824 and is one of the most primitive meteorites known. Pallas's visible and near-infrared spectrum is almost flat, being slightly brighter in towards the blue. There is only one clear absorption band in the 3-micron part, which suggests an anhydrous component mixed with hydrated CM-like silicates.
Pallas's surface is most likely composed of a silicate material; its spectrum and calculated density () correspond to CM chondrite meteorites (), suggesting a mineral composition similar to that of Ceres, but significantly less hydrated.
To within observational limits, Pallas appears to be saturated with craters. Its high inclination and eccentricity means that average impacts are much more energetic than on Vesta or Ceres (with on average twice their velocity), meaning that smaller (and thus more common) impactors can create equivalently sized craters. Indeed, Pallas appears to have many more large craters than either Vesta or Ceres, with craters larger than 40 km covering at least 9% of its surface.
Pallas's shape departs significantly from the dimensions of an equilibrium body at its current rotational period, indicating that it is not a dwarf planet. It's possible that a suspected large impact basin at the south pole, which ejected of the volume of Pallas (twice the volume of the Rheasilvia basin on Vesta), may have increased its inclination and slowed its rotation; the shape of Pallas without such a basin would be close to an equilibrium shape for a 6.2-hour rotational period. A smaller crater near the equator is associated with the Palladian family of asteroids. | 2 Pallas | Wikipedia | 449 | 47262 | https://en.wikipedia.org/wiki/2%20Pallas | Physical sciences | Solar System | Astronomy |
Pallas probably has a quite homogeneous interior. The close match between Pallas and CM chondrites suggests that they formed in the same era and that the interior of Pallas never reached the temperature (≈820 K) needed to dehydrate silicates, which would be necessary to differentiate a dry silicate core beneath a hydrated mantle. Thus Pallas should be rather homogeneous in composition, though some upward flow of water could have occurred since. Such a migration of water to the surface would have left salt deposits, potentially explaining Pallas's relatively high albedo. Indeed, one bright spot is reminiscent of those found on Ceres. Although other explanations for the bright spot are possible (e.g. a recent ejecta blanket), if the near-Earth asteroid 3200 Phaethon is an ejected piece of Pallas, as some have theorized, then a Palladian surface enriched in salts would explain the sodium abundance in the Geminid meteor shower caused by Phaethon.
Surface features
Besides one bright spot in the southern hemisphere, the only surface features identified on Pallas are craters. As of 2020, 36 craters have been identified, 34 of which are larger than 40 km in diameter. Provisional names have been provided for some of them. The craters are named after ancient weapons.
Satellites
A small moon about 1 kilometer in diameter was suggested based on occultation data from 29 May 1978. In 1980, speckle interferometry suggested a much larger satellite, whose existence was refuted a few years later with occultation data.
Exploration
Pallas itself has never been visited by spacecraft. Proposals have been made in the past though none have come to fruition. A flyby of the Dawn probe's visits to 4 Vesta and 1 Ceres was discussed but was not possible due to the high orbital inclination of Pallas. The proposed Athena SmallSat mission would have been launched in 2022 as a secondary payload of the Psyche mission and travel on separate trajectory to a flyby encounter with 2 Pallas, though was not funded due to being outcompeted by other mission concepts such as the TransOrbital Trailblazer Lunar Orbiter. The authors of the proposal cited Pallas as the "largest unexplored" main-belt protoplanet.
Gallery | 2 Pallas | Wikipedia | 469 | 47262 | https://en.wikipedia.org/wiki/2%20Pallas | Physical sciences | Solar System | Astronomy |
243 Ida is an asteroid in the Koronis family of the asteroid belt. It was discovered on 29 September 1884 by Austrian astronomer Johann Palisa at Vienna Observatory and named after a nymph from Greek mythology. Later telescopic observations categorized Ida as an S-type asteroid, the most numerous type in the inner asteroid belt. On 28 August 1993, Ida was visited by the uncrewed Galileo spacecraft while en route to Jupiter. It was the second asteroid visited by a spacecraft and the first found to have a natural satellite.
Ida's orbit lies between the planets Mars and Jupiter, like all main-belt asteroids. Its orbital period is 4.84 years, and its rotation period is 4.63 hours. Ida has an average diameter of . It is irregularly shaped and elongated, apparently composed of two large objects connected together. Its surface is one of the most heavily cratered in the Solar System, featuring a wide variety of crater sizes and ages.
Ida's moon Dactyl was discovered by mission member Ann Harch in images returned from Galileo. It was named after the Dactyls, creatures which inhabited Mount Ida in Greek mythology. Dactyl is only in diameter, about 1/20 the size of Ida. Its orbit around Ida could not be determined with much accuracy, but the constraints of possible orbits allowed a rough determination of Ida's density and revealed that it is depleted of metallic minerals. Dactyl and Ida share many characteristics, suggesting a common origin.
The images returned from Galileo and the subsequent measurement of Ida's mass provided new insights into the geology of S-type asteroids. Before the Galileo flyby, many different theories had been proposed to explain their mineral composition. Determining their composition permits a correlation between meteorites falling to the Earth and their origin in the asteroid belt. Data returned from the flyby pointed to S-type asteroids as the source for the ordinary chondrite meteorites, the most common type found on the Earth's surface.
Discovery and observations
Ida was discovered on 29 September 1884 by Austrian astronomer Johann Palisa at the Vienna Observatory. It was his 45th asteroid discovery. Ida was named by Moriz von Kuffner, a Viennese brewer and amateur astronomer. In Greek mythology, Ida was a nymph of Crete who raised the god Zeus. Ida was recognized as a member of the Koronis family by Kiyotsugu Hirayama, who proposed in 1918 that the group comprised the remnants of a destroyed precursor body. | 243 Ida | Wikipedia | 506 | 47263 | https://en.wikipedia.org/wiki/243%20Ida | Physical sciences | Solar System | Astronomy |
Ida's reflection spectrum was measured on 16 September 1980 by astronomers David J. Tholen and Edward F. Tedesco as part of the eight-color asteroid survey (ECAS). Its spectrum matched those of the asteroids in the S-type classification. Many observations of Ida were made in early 1993 by the US Naval Observatory in Flagstaff and the Oak Ridge Observatory. These improved the measurement of Ida's orbit around the Sun and reduced the uncertainty of its position during the Galileo flyby from .
Exploration
Galileo flyby
Ida was visited in 1993 by the Jupiter-bound space probe Galileo. Its encounters of the asteroids Gaspra and Ida were secondary to the Jupiter mission. These were selected as targets in response to a new NASA policy directing mission planners to consider asteroid flybys for all spacecraft crossing the belt. No prior missions had attempted such a flyby. Galileo was launched into orbit by the Space Shuttle Atlantis mission STS-34 on 18 October 1989. Changing Galileo's trajectory to approach Ida required that it consume of propellant. Mission planners delayed the decision to attempt a flyby until they were certain that this would leave the spacecraft enough propellant to complete its Jupiter mission.
Galileo's trajectory carried it into the asteroid belt twice on its way to Jupiter. During its second crossing, it flew by Ida on 28 August 1993 at a speed of relative to the asteroid. The onboard imager observed Ida from a distance of to its closest approach of . Ida was the second asteroid, after Gaspra, to be imaged by a spacecraft. About 95% of Ida's surface came into view of the probe during the flyby.
Transmission of many Ida images was delayed due to a permanent failure in the spacecraft's high-gain antenna. The first five images were received in September 1993. These comprised a high-resolution mosaic of the asteroid at a resolution of 31–38 m/pixel. The remaining images were sent in February 1994, when the spacecraft's proximity to the Earth allowed higher speed transmissions.
Discoveries
The data returned from the Galileo flybys of Gaspra and Ida, and the later NEAR Shoemaker asteroid mission, permitted the first study of asteroid geology. Ida's relatively large surface exhibited a diverse range of geological features. The discovery of Ida's moon Dactyl, the first confirmed satellite of an asteroid, provided additional insights into Ida's composition. | 243 Ida | Wikipedia | 481 | 47263 | https://en.wikipedia.org/wiki/243%20Ida | Physical sciences | Solar System | Astronomy |
Ida is classified as an S-type asteroid based on ground-based spectroscopic measurements. The composition of S-types was uncertain before the Galileo flybys, but was interpreted to be either of two minerals found in meteorites that had fallen to the Earth: ordinary chondrite (OC) and stony-iron. Estimates of Ida's density are constrained to less than 3.2 g/cm3 by the long-term stability of Dactyl's orbit. This all but rules out a stony-iron composition; were Ida made of 5 g/cm3 iron- and nickel-rich material, it would have to contain more than 40% empty space.
The Galileo images also led to the discovery that space weathering was taking place on Ida, a process which causes older regions to become more red in color over time. The same process affects both Ida and its moon, although Dactyl shows a lesser change. The weathering of Ida's surface revealed another detail about its composition: the reflection spectra of freshly exposed parts of the surface resembled that of OC meteorites, but the older regions matched the spectra of S-type asteroids.Both of these discoveries—the space weathering effects and the low density—led to a new understanding about the relationship between S-type asteroids and OC meteorites. S-types are the most numerous kind of asteroid in the inner part of the asteroid belt. OC meteorites are, likewise, the most common type of meteorite found on the Earth's surface. The reflection spectra measured by remote observations of S-type asteroids, however, did not match that of OC meteorites. The Galileo flyby of Ida found that some S-types, particularly the Koronis family, could be the source of these meteorites.
Physical characteristics
Ida's mass is between 3.65 and 4.99 × 1016 kg. Its gravitational field produces an acceleration of about 0.3 to 1.1 cm/s2 over its surface. This field is so weak that an astronaut standing on its surface could leap from one end of Ida to the other, and an object moving in excess of could escape the asteroid entirely. | 243 Ida | Wikipedia | 445 | 47263 | https://en.wikipedia.org/wiki/243%20Ida | Physical sciences | Solar System | Astronomy |
Ida is a distinctly elongated asteroid, with an irregular surface. Ida is 2.35 times as long as it is wide, and a "waist" separates it into two geologically dissimilar halves. This constricted shape is consistent with Ida being made of two large, solid components, with loose debris filling the gap between them. However, no such debris was seen in high-resolution images captured by Galileo. Although there are a few steep slopes tilting up to about 50° on Ida, the slope generally does not exceed 35°. Ida's irregular shape is responsible for the asteroid's very uneven gravitational field. The surface acceleration is lowest at the extremities because of their high rotational speed. It is also low near the "waist" because the mass of the asteroid is concentrated in the two halves, away from this location.
Surface features
Ida's surface appears heavily cratered and mostly gray, although minor color variations mark newly formed or uncovered areas. Besides craters, other features are evident, such as grooves, ridges, and protrusions. Ida is covered by a thick layer of regolith, loose debris that obscures the solid rock beneath. The largest, boulder-sized, debris fragments are called ejecta blocks, several of which have been observed on the surface.
Regolith
The surface of Ida is covered in a blanket of pulverized rock, called regolith, about thick. This material is produced in impact events and redistributed across Ida's surface by geological processes. Galileo observed evidence of recent downslope regolith movement.
Ida's regolith is composed of the silicate minerals olivine and pyroxene. Its appearance changes over time through a process called space weathering. Because of this process, older regolith appears more red in color compared to freshly exposed material.
About 20 large (40–150 m across) ejecta blocks have been identified, embedded in Ida's regolith. Ejecta blocks constitute the largest pieces of the regolith. Because ejecta blocks are expected to break down quickly by impact events, those present on the surface must have been either formed recently or uncovered by an impact event. Most of them are located within the craters Lascaux and Mammoth, but they may not have been produced there. This area attracts debris due to Ida's irregular gravitational field. Some blocks may have been ejected from the young crater Azzurra on the opposite side of the asteroid. | 243 Ida | Wikipedia | 512 | 47263 | https://en.wikipedia.org/wiki/243%20Ida | Physical sciences | Solar System | Astronomy |
Structures
Several major structures mark Ida's surface. The asteroid appears to be split into two halves, here referred to as region 1 and region 2, connected by a "waist". This feature may have been filled in by debris, or blasted out of the asteroid by impacts.
Region 1 of Ida contains two major structures. One is a prominent ridge named Townsend Dorsum that stretches 150 degrees around Ida's surface. The other structure is a large indentation named Vienna Regio.
Ida's region 2 features several sets of grooves, most of which are wide or less and up to long. They are located near, but are not connected with, the craters Mammoth, Lascaux, and Kartchner. Some grooves are related to major impact events, for example a set opposite Vienna Regio.
Craters
Ida is one of the most densely cratered bodies yet explored in the Solar System, and impacts have been the primary process shaping its surface. Cratering has reached the saturation point, meaning that new impacts erase evidence of old ones, leaving the total crater count roughly the same. It is covered with craters of all sizes and stages of degradation, and ranging in age from fresh to as old as Ida itself. The oldest may have been formed during the breakup of the Koronis family parent body. The largest crater, Lascaux, is almost across. Region 2 contains nearly all of the craters larger than in diameter, but Region 1 has no large craters at all. Some craters are arranged in chains.
Ida's major craters are named after caves and lava tubes on Earth. The crater Azzurra, for example, is named after a submerged cave on the island of Capri, also known as the Blue Grotto. Azzurra seems to be the most recent major impact on Ida. The ejecta from this collision is distributed discontinuously over Ida and is responsible for the large-scale color and albedo variations across its surface. An exception to the crater morphology is the fresh, asymmetric Fingal, which has a sharp boundary between the floor and wall on one side. Another significant crater is Afon, which marks Ida's prime meridian. | 243 Ida | Wikipedia | 442 | 47263 | https://en.wikipedia.org/wiki/243%20Ida | Physical sciences | Solar System | Astronomy |
The craters are simple in structure: bowl-shaped with no flat bottoms and no central peaks. They are distributed evenly around Ida, except for a protrusion north of crater Choukoutien which is smoother and less cratered. The ejecta excavated by impacts is deposited differently on Ida than on planets because of its rapid rotation, low gravity and irregular shape. Ejecta blankets settle asymmetrically around their craters, but fast-moving ejecta that escapes from the asteroid is permanently lost.
Composition
Ida was classified as an S-type asteroid based on the similarity of its reflectance spectra with similar asteroids. S-types may share their composition with stony-iron or ordinary chondrite (OC) meteorites. The composition of the interior has not been directly analyzed, but is assumed to be similar to OC material based on observed surface color changes and Ida's bulk density of 2.27–3.10 g/cm3. OC meteorites contain varying amounts of the silicates olivine and pyroxene, iron, and feldspar. Olivine and pyroxene were detected on Ida by Galileo. The mineral content appears to be homogeneous throughout its extent. Galileo found minimal variations on the surface, and the asteroid's spin indicates a consistent density. Assuming that its composition is similar to OC meteorites, which range in density from 3.48 to 3.64 g/cm3, Ida would have a porosity of 11–42%.
Ida's interior probably contains some amount of impact-fractured rock, called megaregolith. The megaregolith layer of Ida extends between hundreds of meters below the surface to a few kilometers. Some rock in Ida's core may have been fractured below the large craters Mammoth, Lascaux, and Undara.
Orbit and rotation
Ida is a member of the Koronis family of asteroid-belt asteroids. Ida orbits the Sun at an average distance of , between the orbits of Mars and Jupiter. Ida takes 4.84089 years to complete one orbit. | 243 Ida | Wikipedia | 426 | 47263 | https://en.wikipedia.org/wiki/243%20Ida | Physical sciences | Solar System | Astronomy |
Ida rotates in the retrograde direction with a rotation period of 4.63 hours (roughly 5 hours). The calculated maximum moment of inertia of a uniformly dense object the same shape as Ida coincides with the spin axis of the asteroid. This suggests that there are no major variations of density within the asteroid. Ida's axis of rotation precesses with a period of 77 thousand years, due to the gravity of the Sun acting upon the nonspherical shape of the asteroid.
Origin
Ida originated in the breakup of the roughly diameter Koronis parent body. The progenitor asteroid had partially differentiated, with heavier metals migrating to the core. Ida carried away insignificant amounts of this core material. It is uncertain how long ago the disruption event occurred. According to an analysis of Ida's cratering processes, its surface is more than a billion years old. However, this is inconsistent with the estimated age of the Ida–Dactyl system of less than 100 million years; it is unlikely that Dactyl, due to its small size, could have escaped being destroyed in a major collision for longer. The difference in age estimates may be explained by an increased rate of cratering from the debris of the Koronis parent body's destruction.
Dactyl
Ida has a moon named Dactyl, official designation (243) Ida I Dactyl. It was discovered in images taken by the Galileo spacecraft during its flyby in 1993. These images provided the first direct confirmation of an asteroid moon. At the time, it was separated from Ida by a distance of , moving in a prograde orbit. Dactyl is heavily cratered, like Ida, and consists of similar materials. Its origin is uncertain, but evidence from the flyby suggests that it originated as a fragment of the Koronis parent body.
Discovery
Dactyl was found on 17 February 1994 by Galileo mission member Ann Harch, while examining delayed image downloads from the spacecraft. Galileo recorded 47 images of Dactyl over an observation period of 5.5 hours in August 1993. The spacecraft was from Ida and from Dactyl when the first image of the moon was captured, 14 minutes before Galileo made its closest approach.
Dactyl was initially designated 1993 (243) 1. It was named by the International Astronomical Union in 1994, for the mythological dactyls who inhabited Mount Ida on the island of Crete. | 243 Ida | Wikipedia | 489 | 47263 | https://en.wikipedia.org/wiki/243%20Ida | Physical sciences | Solar System | Astronomy |
Physical characteristics
Dactyl is an "egg-shaped" but "remarkably spherical" object measuring . It is oriented with its longest axis pointing towards Ida. Like Ida, Dactyl's surface exhibits saturation cratering. It is marked by more than a dozen craters with a diameter greater than , indicating that the moon has suffered many collisions during its history. At least six craters form a linear chain, suggesting that it was caused by locally produced debris, possibly ejected from Ida. Dactyl's craters may contain central peaks, unlike those found on Ida. These features, and Dactyl's spheroidal shape, imply that the moon is gravitationally controlled despite its small size. Like Ida, its average temperature is about .
Dactyl shares many characteristics with Ida. Their albedos and reflection spectra are very similar. The small differences indicate that the space weathering process is less active on Dactyl. Its small size would make the formation of significant amounts of regolith impossible. This contrasts with Ida, which is covered by a deep layer of regolith.
The two largest imaged craters on Dactyl were named Acmon and Celmis , after two of the mythological dactyls. Acmon is the largest crater in the above image, and Celmis is near the bottom of the image, mostly obscured in shadow. The craters are 300 and 200 meters in diameter, respectively.
Orbit
Dactyl's orbit around Ida is not precisely known. Galileo was in the plane of Dactyl's orbit when most of the images were taken, which made determining its exact orbit difficult. Dactyl orbits in the prograde direction and is inclined about 8° to Ida's equator. Based on computer simulations, Dactyl's pericenter must be more than about from Ida for it to remain in a stable orbit. The range of orbits generated by the simulations was narrowed down by the necessity of having the orbits pass through points at which Galileo observed Dactyl to be at 16:52:05 UT on 28 August 1993, about from Ida at longitude 85°. On 26 April 1994, the Hubble Space Telescope observed Ida for eight hours and was unable to spot Dactyl. It would have been able to observe it if it were more than about from Ida. | 243 Ida | Wikipedia | 475 | 47263 | https://en.wikipedia.org/wiki/243%20Ida | Physical sciences | Solar System | Astronomy |
If in a circular orbit at the distance at which it was seen, Dactyl's orbital period would be about 20 hours. Its orbital speed is roughly , "about the speed of a fast run or a slowly thrown baseball".
Age and origin
Dactyl may have originated at the same time as Ida, from the disruption of the Koronis parent body. However, it may have formed more recently, perhaps as ejecta from a large impact on Ida. It is extremely unlikely that it was captured by Ida. Dactyl may have suffered a major impact around 100 million years ago, which reduced its size. | 243 Ida | Wikipedia | 127 | 47263 | https://en.wikipedia.org/wiki/243%20Ida | Physical sciences | Solar System | Astronomy |
The asteroid belt is a torus-shaped region in the Solar System, centered on the Sun and roughly spanning the space between the orbits of the planets Jupiter and Mars. It contains a great many solid, irregularly shaped bodies called asteroids or minor planets. The identified objects are of many sizes, but much smaller than planets, and, on average, are about one million kilometers (or six hundred thousand miles) apart. This asteroid belt is also called the main asteroid belt or main belt to distinguish it from other asteroid populations in the Solar System.
The asteroid belt is the smallest and innermost known circumstellar disc in the Solar System. Classes of small Solar System bodies in other regions are the near-Earth objects, the centaurs, the Kuiper belt objects, the scattered disc objects, the sednoids, and the Oort cloud objects. About 60% of the main belt mass is contained in the four largest asteroids: Ceres, Vesta, Pallas, and Hygiea. The total mass of the asteroid belt is estimated to be 3% that of the Moon.
Ceres, the only object in the asteroid belt large enough to be a dwarf planet, is about 950 km in diameter, whereas Vesta, Pallas, and Hygiea have mean diameters less than 600 km. The remaining mineralogically classified bodies range in size down to a few metres. The asteroid material is so thinly distributed that numerous uncrewed spacecraft have traversed it without incident. Nonetheless, collisions between large asteroids occur and can produce an asteroid family, whose members have similar orbital characteristics and compositions. Individual asteroids within the belt are categorized by their spectra, with most falling into three basic groups: carbonaceous (C-type), silicate (S-type), and metal-rich (M-type). | Asteroid belt | Wikipedia | 376 | 47264 | https://en.wikipedia.org/wiki/Asteroid%20belt | Physical sciences | Solar System | null |
The asteroid belt formed from the primordial solar nebula as a group of planetesimals, the smaller precursors of the protoplanets. However, between Mars and Jupiter gravitational perturbations from Jupiter disrupted their accretion into a planet, imparting excess kinetic energy which shattered colliding planetesimals and most of the incipient protoplanets. As a result, 99.9% of the asteroid belt's original mass was lost in the first 100 million years of the Solar System's history. Some fragments eventually found their way into the inner Solar System, leading to meteorite impacts with the inner planets. Asteroid orbits continue to be appreciably perturbed whenever their period of revolution about the Sun forms an orbital resonance with Jupiter. At these orbital distances, a Kirkwood gap occurs as they are swept into other orbits.
History of observation
In 1596, Johannes Kepler wrote, "Between Mars and Jupiter, I place a planet," in his Mysterium Cosmographicum, stating his prediction that a planet would be found there. While analyzing Tycho Brahe's data, Kepler thought that too large a gap existed between the orbits of Mars and Jupiter to fit his own model of where planetary orbits should be found.
In an anonymous footnote to his 1766 translation of Charles Bonnet's Contemplation de la Nature, the astronomer Johann Daniel Titius of Wittenberg noted an apparent pattern in the layout of the planets, now known as the Titius-Bode Law. If one began a numerical sequence at 0, then included 3, 6, 12, 24, 48, etc., doubling each time, and added four to each number and divided by 10, this produced a remarkably close approximation to the radii of the orbits of the known planets as measured in astronomical units, provided one allowed for a "missing planet" (equivalent to 24 in the sequence) between the orbits of Mars (12) and Jupiter (48). In his footnote, Titius declared, "But should the Lord Architect have left that space empty? Not at all." When William Herschel discovered Uranus in 1781, the planet's orbit closely matched the law, leading some astronomers to conclude that a planet had to be between the orbits of Mars and Jupiter. | Asteroid belt | Wikipedia | 471 | 47264 | https://en.wikipedia.org/wiki/Asteroid%20belt | Physical sciences | Solar System | null |
On January 1, 1801, Giuseppe Piazzi, chairman of astronomy at the University of Palermo, Sicily, found a tiny moving object in an orbit with exactly the radius predicted by this pattern. He dubbed it "Ceres", after the Roman goddess of the harvest and patron of Sicily. Piazzi initially believed it to be a comet, but its lack of a coma suggested it was a planet.
Thus, the aforementioned pattern predicted the semimajor axes of all eight planets of the time (Mercury, Venus, Earth, Mars, Ceres, Jupiter, Saturn, and Uranus). Concurrent with the discovery of Ceres, an informal group of 24 astronomers dubbed the "celestial police" was formed under the invitation of Franz Xaver von Zach with the express purpose of finding additional planets; they focused their search for them in the region between Mars and Jupiter where the Titius–Bode law predicted there should be a planet.
About 15 months later, Heinrich Olbers, a member of the celestial police, discovered a second object in the same region, Pallas. Unlike the other known planets, Ceres and Pallas remained points of light even under the highest telescope magnifications instead of resolving into discs. Apart from their rapid movement, they appeared indistinguishable from stars.
Accordingly, in 1802, William Herschel suggested they be placed into a separate category, named "asteroids", after the Greek asteroeides, meaning "star-like". Upon completing a series of observations of Ceres and Pallas, he concluded,
Neither the appellation of planets nor that of comets can with any propriety of language be given to these two stars ... They resemble small stars so much as hardly to be distinguished from them. From this, their asteroidal appearance, if I take my name, and call them Asteroids; reserving for myself, however, the liberty of changing that name, if another, more expressive of their nature, should occur.
By 1807, further investigation revealed two new objects in the region: Juno and Vesta. The burning of Lilienthal in the Napoleonic wars, where the main body of work had been done, brought this first period of discovery to a close. | Asteroid belt | Wikipedia | 451 | 47264 | https://en.wikipedia.org/wiki/Asteroid%20belt | Physical sciences | Solar System | null |
Despite Herschel's coinage, for several decades it remained common practice to refer to these objects as planets and to prefix their names with numbers representing their sequence of discovery: 1 Ceres, 2 Pallas, 3 Juno, 4 Vesta. In 1845, though, the astronomer Karl Ludwig Hencke detected a fifth object (5 Astraea) and, shortly thereafter, new objects were found at an accelerating rate. Counting them among the planets became increasingly cumbersome. Eventually, they were dropped from the planet list (as first suggested by Alexander von Humboldt in the early 1850s) and Herschel's coinage, "asteroids", gradually came into common use.
The discovery of Neptune in 1846 led to the discrediting of the Titius–Bode law in the eyes of scientists because its orbit was nowhere near the predicted position. To date, no scientific explanation for the law has been given, and astronomers' consensus regards it as a coincidence.
[[File:951 Gaspra.jpg|right|thumb|951 Gaspra, the first asteroid imaged by a spacecraft, as viewed during Galileo'''s 1991 flyby; colors are exaggerated]]
The expression "asteroid belt" came into use in the early 1850s, although pinpointing who coined the term is difficult. The first English use seems to be in the 1850 translation (by Elise Otté) of Alexander von Humboldt's Cosmos: "[...] and the regular appearance, about the 13th of November and the 11th of August, of shooting stars, which probably form part of a belt of asteroids intersecting the Earth's orbit and moving with planetary velocity". Another early appearance occurred in Robert James Mann's A Guide to the Knowledge of the Heavens: "The orbits of the asteroids are placed in a wide belt of space, extending between the extremes of [...]". The American astronomer Benjamin Peirce seems to have adopted that terminology and to have been one of its promoters.
Over 100 asteroids had been located by mid-1868, and in 1891, the introduction of astrophotography by Max Wolf accelerated the rate of discovery. A total of 1,000 asteroids had been found by 1921, 10,000 by 1981, and 100,000 by 2000. Modern asteroid survey systems now use automated means to locate new minor planets in ever-increasing numbers. | Asteroid belt | Wikipedia | 480 | 47264 | https://en.wikipedia.org/wiki/Asteroid%20belt | Physical sciences | Solar System | null |
On 22 January 2014, European Space Agency (ESA) scientists reported the detection, for the first definitive time, of water vapor on Ceres, the largest object in the asteroid belt. The detection was made by using the far-infrared abilities of the Herschel Space Observatory. The finding was unexpected because comets, not asteroids, are typically considered to "sprout jets and plumes". According to one of the scientists, "The lines are becoming more and more blurred between comets and asteroids".
Origin
Formation
In 1802, shortly after discovering Pallas, Olbers suggested to Herschel and Carl Gauss that Ceres and Pallas were fragments of a much larger planet that once occupied the Mars–Jupiter region, with this planet having suffered an internal explosion or a cometary impact many million years before, while Odesan astronomer K. N. Savchenko suggested that Ceres, Pallas, Juno, and Vesta were escaped moons rather than fragments of the exploded planet. The large amount of energy required to destroy a planet, combined with the belt's low combined mass, which is only about 4% of the mass of Earth's Moon, does not support these hypotheses. Further, the significant chemical differences between the asteroids become difficult to explain if they come from the same planet.
A modern hypothesis for the asteroid belt's creation relates to how, in general for the Solar System, planetary formation is thought to have occurred via a process comparable to the long-standing nebular hypothesis; a cloud of interstellar dust and gas collapsed under the influence of gravity to form a rotating disc of material that then conglomerated to form the Sun and planets. During the first few million years of the Solar System's history, an accretion process of sticky collisions caused the clumping of small particles, which gradually increased in size. Once the clumps reached sufficient mass, they could draw in other bodies through gravitational attraction and become planetesimals. This gravitational accretion led to the formation of the planets. | Asteroid belt | Wikipedia | 411 | 47264 | https://en.wikipedia.org/wiki/Asteroid%20belt | Physical sciences | Solar System | null |
Planetesimals within the region that would become the asteroid belt were strongly perturbed by Jupiter's gravity. Orbital resonances occurred where the orbital period of an object in the belt formed an integer fraction of the orbital period of Jupiter, perturbing the object into a different orbit; the region lying between the orbits of Mars and Jupiter contains many such orbital resonances. As Jupiter migrated inward following its formation, these resonances would have swept across the asteroid belt, dynamically exciting the region's population and increasing their velocities relative to each other. In regions where the average velocity of the collisions was too high, the shattering of planetesimals tended to dominate over accretion, preventing the formation of a planet. Instead, they continued to orbit the Sun as before, occasionally colliding.
During the early history of the Solar System, the asteroids melted to some degree, allowing elements within them to be differentiated by mass. Some of the progenitor bodies may even have undergone periods of explosive volcanism and formed magma oceans. Because of the relatively small size of the bodies, though, the period of melting was necessarily brief compared to the much larger planets, and had generally ended about 4.5 billion years ago, in the first tens of millions of years of formation. In August 2007, a study of zircon crystals in an Antarctic meteorite believed to have originated from Vesta suggested that it, and by extension the rest of the asteroid belt, had formed rather quickly, within 10 million years of the Solar System's origin.
Evolution
The asteroids are not pristine samples of the primordial Solar System. They have undergone considerable evolution since their formation, including internal heating (in the first few tens of millions of years), surface melting from impacts, space weathering from radiation, and bombardment by micrometeorites. Although some scientists refer to the asteroids as residual planetesimals, other scientists consider them distinct.
The current asteroid belt is believed to contain only a small fraction of the mass of the primordial belt. Computer simulations suggest that the original asteroid belt may have contained mass equivalent to the Earth's. Primarily because of gravitational perturbations, most of the material was ejected from the belt within about 1 million years of formation, leaving behind less than 0.1% of the original mass. Since its formation, the size distribution of the asteroid belt has remained relatively stable; no significant increase or decrease in the typical dimensions of the main-belt asteroids has occurred. | Asteroid belt | Wikipedia | 509 | 47264 | https://en.wikipedia.org/wiki/Asteroid%20belt | Physical sciences | Solar System | null |
The 4:1 orbital resonance with Jupiter, at a radius 2.06 astronomical units (AUs), can be considered the inner boundary of the asteroid belt. Perturbations by Jupiter send bodies straying there into unstable orbits. Most bodies formed within the radius of this gap were swept up by Mars (which has an aphelion at 1.67 AU) or ejected by its gravitational perturbations in the early history of the Solar System. The Hungaria asteroids lie closer to the Sun than the 4:1 resonance, but are protected from disruption by their high inclination.
When the asteroid belt was first formed, the temperatures at a distance of 2.7 AU from the Sun formed a "snow line" below the freezing point of water. Planetesimals formed beyond this radius were able to accumulate ice.
In 2006, a population of comets had been discovered within the asteroid belt beyond the snow line, which may have provided a source of water for Earth's oceans. According to some models, outgassing of water during the Earth's formative period was insufficient to form the oceans, requiring an external source such as a cometary bombardment.
The outer asteroid belt appears to include a few objects that may have arrived there during the last few hundred years, the list includes also known as 362P.
Characteristics
Contrary to popular imagery, the asteroid belt is mostly empty. The asteroids are spread over such a large volume that reaching an asteroid without aiming carefully would be improbable. Nonetheless, hundreds of thousands of asteroids are currently known, and the total number ranges in the millions or more, depending on the lower size cutoff. Over 200 asteroids are known to be larger than 100 km, and a survey in the infrared wavelengths has shown that the asteroid belt has between 700,000 and 1.7 million asteroids with a diameter of 1 km or more.
The number of asteroids in the main belt steadily increases with decreasing size. Although the size distribution generally follows a power law, there are 'bumps' in the curve at about and , where more asteroids than expected from such a curve are found. Most asteroids larger than approximately in diameter are primordial, having survived from the accretion epoch, whereas most smaller asteroids are products of fragmentation of primordial asteroids. The primordial population of the main belt was probably 200 times what it is today. | Asteroid belt | Wikipedia | 479 | 47264 | https://en.wikipedia.org/wiki/Asteroid%20belt | Physical sciences | Solar System | null |
The absolute magnitudes of most of the known asteroids are between 11 and 19, with the median at about 16. On average the distance between the asteroids is about , although this varies among asteroid families and smaller undetected asteroids might be even closer. The total mass of the asteroid belt is estimated to be kg, which is 3% of the mass of the Moon. The four largest objects, Ceres, Vesta, Pallas, and Hygiea, contain an estimated 62% of the belt's total mass, with 39% accounted for by Ceres alone.For recent estimates of the masses of Ceres, Vesta, Pallas and Hygiea, see the references in the infoboxes of their respective articles.
Composition
The present day belt consists primarily of three categories of asteroids: C-type carbonaceous asteroids, S-type silicate asteroids, and a hybrid group of X-type asteroids. The hybrid group have featureless spectra, but they can be divided into three groups based on reflectivity, yielding the M-type metallic, P-type primitive, and E-type enstatite asteroids. Additional types have been found that do not fit within these primary classes. There is a compositional trend of asteroid types by increasing distance from the Sun, in the order of S, C, P, and the spectrally-featureless D-types.
Carbonaceous asteroids, as their name suggests, are carbon-rich. They dominate the asteroid belt's outer regions, and are rare in the inner belt. Together they comprise over 75% of the visible asteroids. They are redder in hue than the other asteroids and have a low albedo. Their surface compositions are similar to carbonaceous chondrite meteorites. Chemically, their spectra match the primordial composition of the early Solar System, with hydrogen, helium, and volatiles removed.
S-type (silicate-rich) asteroids are more common toward the inner region of the belt, within 2.5 AU of the Sun. The spectra of their surfaces reveal the presence of silicates and some metal, but no significant carbonaceous compounds. This indicates that their materials have been significantly modified from their primordial composition, probably through melting and reformation. They have a relatively high albedo and form about 17% of the total asteroid population. | Asteroid belt | Wikipedia | 477 | 47264 | https://en.wikipedia.org/wiki/Asteroid%20belt | Physical sciences | Solar System | null |
M-type (metal-rich) asteroids are typically found in the middle of the main belt, and they make up much of the remainder of the total population. Their spectra resemble that of iron-nickel. Some are believed to have formed from the metallic cores of differentiated progenitor bodies that were disrupted through collision. However, some silicate compounds also can produce a similar appearance. For example, the large M-type asteroid 22 Kalliope does not appear to be primarily composed of metal. Within the asteroid belt, the number distribution of M-type asteroids peaks at a semimajor axis of about 2.7 AU. Whether all M-types are compositionally similar, or whether it is a label for several varieties which do not fit neatly into the main C and S classes is not yet clear.
One mystery is the relative rarity of V-type (Vestoid) or basaltic asteroids in the asteroid belt. Theories of asteroid formation predict that objects the size of Vesta or larger should form crusts and mantles, which would be composed mainly of basaltic rock, resulting in more than half of all asteroids being composed either of basalt or of olivine. However, observations suggest that 99% of the predicted basaltic material is missing. Until 2001, most basaltic bodies discovered in the asteroid belt were believed to originate from the asteroid Vesta (hence their name V-type), but the discovery of the asteroid 1459 Magnya revealed a slightly different chemical composition from the other basaltic asteroids discovered until then, suggesting a different origin. This hypothesis was reinforced by the further discovery in 2007 of two asteroids in the outer belt, 7472 Kumakiri and , with a differing basaltic composition that could not have originated from Vesta. These two are the only V-type asteroids discovered in the outer belt to date.
The temperature of the asteroid belt varies with the distance from the Sun. For dust particles within the belt, typical temperatures range from 200 K (−73 °C) at 2.2 AU down to 165 K (−108 °C) at 3.2 AU. However, due to rotation, the surface temperature of an asteroid can vary considerably as the sides are alternately exposed to solar radiation then to the stellar background.
Main-belt comets | Asteroid belt | Wikipedia | 463 | 47264 | https://en.wikipedia.org/wiki/Asteroid%20belt | Physical sciences | Solar System | null |
Several otherwise unremarkable bodies in the outer belt show cometary activity. Because their orbits cannot be explained through the capture of classical comets, many of the outer asteroids are thought to be icy, with the ice occasionally exposed to sublimation through small impacts. Main-belt comets may have been a major source of the Earth's oceans because the deuterium-hydrogen ratio is too low for classical comets to have been the principal source.
Orbits
Most asteroids within the asteroid belt have orbital eccentricities of less than 0.4, and an inclination of less than 30°. The orbital distribution of the asteroids reaches a maximum at an eccentricity around 0.07 and an inclination below 4°. Thus, although a typical asteroid has a relatively circular orbit and lies near the plane of the ecliptic, some asteroid orbits can be highly eccentric or travel well outside the ecliptic plane.
Sometimes, the term "main belt" is used to refer only to the more compact "core" region where the greatest concentration of bodies is found. This lies between the strong 4:1 and 2:1 Kirkwood gaps at 2.06 and 3.27 AU, and at orbital eccentricities less than roughly 0.33, along with orbital inclinations below about 20°. , this "core" region contained 93% of all discovered and numbered minor planets within the Solar System. The JPL Small-Body Database lists over 1 million known main-belt asteroids.
Kirkwood gaps
The semimajor axis of an asteroid is used to describe the dimensions of its orbit around the Sun, and its value determines the minor planet's orbital period. In 1866, Daniel Kirkwood announced the discovery of gaps in the distances of these bodies' orbits from the Sun. They were located in positions where their period of revolution about the Sun was an integer fraction of Jupiter's orbital period. Kirkwood proposed that the gravitational perturbations of the planet led to the removal of asteroids from these orbits. | Asteroid belt | Wikipedia | 402 | 47264 | https://en.wikipedia.org/wiki/Asteroid%20belt | Physical sciences | Solar System | null |
When the mean orbital period of an asteroid is an integer fraction of the orbital period of Jupiter, a mean-motion resonance with the gas giant is created that is sufficient to perturb an asteroid to new orbital elements. Primordial asteroids entered these gaps because of the migration of Jupiter's orbit. Subsequently, asteroids primarily migrate into these gap orbits due to the Yarkovsky effect, but may also enter because of perturbations or collisions. After entering, an asteroid is gradually nudged into a different, random orbit with a larger or smaller semimajor axis.
Collisions
The high population of the asteroid belt makes for an active environment, where collisions between asteroids occur frequently (on deep time scales). Impact events between main-belt bodies with a mean radius of 10 km are expected to occur about once every 10 million years. A collision may fragment an asteroid into numerous smaller pieces (leading to the formation of a new asteroid family). Conversely, collisions that occur at low relative speeds may also join two asteroids. After more than 4 billion years of such processes, the members of the asteroid belt now bear little resemblance to the original population.
Evidence suggests that most main belt asteroids between 200 m and 10 km in diameter are rubble piles formed by collisions. These bodies consist of a multitude of irregular objects that are mostly bound together by self-gravity, resulting in significant amounts of internal porosity. Along with the asteroid bodies, the asteroid belt also contains bands of dust with particle radii of up to a few hundred micrometres. This fine material is produced, at least in part, from collisions between asteroids, and by the impact of micrometeorites upon the asteroids. Due to the Poynting–Robertson effect, the pressure of solar radiation causes this dust to slowly spiral inward toward the Sun. | Asteroid belt | Wikipedia | 364 | 47264 | https://en.wikipedia.org/wiki/Asteroid%20belt | Physical sciences | Solar System | null |
The combination of this fine asteroid dust, as well as ejected cometary material, produces the zodiacal light. This faint auroral glow can be viewed at night extending from the direction of the Sun along the plane of the ecliptic. Asteroid particles that produce visible zodiacal light average about 40 μm in radius. The typical lifetimes of main-belt zodiacal cloud particles are about 700,000 years. Thus, to maintain the bands of dust, new particles must be steadily produced within the asteroid belt. It was once thought that collisions of asteroids form a major component of the zodiacal light. However, computer simulations by Nesvorný and colleagues attributed 85 percent of the zodiacal-light dust to fragmentations of Jupiter-family comets, rather than to comets and collisions between asteroids in the asteroid belt. At most 10 percent of the dust is attributed to the asteroid belt.
Meteorites
Some of the debris from collisions can form meteoroids that enter the Earth's atmosphere. Of the 50,000 meteorites found on Earth to date, 99.8 percent are believed to have originated in the asteroid belt.
Families and groups
In 1918, the Japanese astronomer Kiyotsugu Hirayama noticed that the orbits of some of the asteroids had similar parameters, forming families or groups.
Approximately one-third of the asteroids in the asteroid belt are members of an asteroid family. These share similar orbital elements, such as semi-major axis, eccentricity, and orbital inclination as well as similar spectral features, which indicate a common origin in the breakup of a larger body. Graphical displays of these element pairs, for members of the asteroid belt, show concentrations indicating the presence of an asteroid family. There are about 20 to 30 associations that are likely asteroid families. Additional groupings have been found that are less certain. Asteroid families can be confirmed when the members display similar spectral features. Smaller associations of asteroids are called groups or clusters. | Asteroid belt | Wikipedia | 386 | 47264 | https://en.wikipedia.org/wiki/Asteroid%20belt | Physical sciences | Solar System | null |
Some of the most prominent families in the asteroid belt (in order of increasing semi-major axes) are the Flora, Eunomia, Koronis, Eos, and Themis families. The Flora family, one of the largest with more than 800 known members, may have formed from a collision less than 1 billion years ago.
The largest asteroid to be a true member of a family is 4 Vesta. (This is in contrast to an interloper, in the case of Ceres with the Gefion family.) The Vesta family is believed to have formed as the result of a crater-forming impact on Vesta. Likewise, the HED meteorites may also have originated from Vesta as a result of this collision.
Three prominent bands of dust have been found within the asteroid belt. These have similar orbital inclinations as the Eos, Koronis, and Themis asteroid families, and so are possibly associated with those groupings.
The main belt evolution after the Late Heavy Bombardment was likely affected by the passages of large Centaurs and trans-Neptunian objects (TNOs). Centaurs and TNOs that reach the inner Solar System can modify the orbits of main belt asteroids, though only if their mass is of the order of for single encounters or, one order less in case of multiple close encounters. However, Centaurs and TNOs are unlikely to have significantly dispersed young asteroid families in the main belt, although they can have perturbed some old asteroid families. Current main belt asteroids that originated as Centaurs or trans-Neptunian objects may lie in the outer belt with short lifetime of less than 4 million years, most likely orbiting between 2.8 and 3.2 AU at larger eccentricities than typical of main belt asteroids.
Periphery
Skirting the inner edge of the belt (ranging between 1.78 and 2.0 AU, with a mean semi-major axis of 1.9 AU) is the Hungaria family of minor planets. They are named after the main member, 434 Hungaria; the group contains at least 52 named asteroids. The Hungaria group is separated from the main body by the 4:1 Kirkwood gap and their orbits have a high inclination. Some members belong to the Mars-crossing category of asteroids, and gravitational perturbations by Mars are likely a factor in reducing the total population of this group. | Asteroid belt | Wikipedia | 490 | 47264 | https://en.wikipedia.org/wiki/Asteroid%20belt | Physical sciences | Solar System | null |
Another high-inclination group in the inner part of the asteroid belt is the Phocaea family. These are composed primarily of S-type asteroids, whereas the neighboring Hungaria family includes some E-types. The Phocaea family orbit between 2.25 and 2.5 AU from the Sun.
Skirting the outer edge of the asteroid belt is the Cybele group, orbiting between 3.3 and 3.5 AU. These have a 7:4 orbital resonance with Jupiter. The Hilda family orbit between 3.5 and 4.2 AU with relatively circular orbits and a stable 3:2 orbital resonance with Jupiter. There are few asteroids beyond 4.2 AU, until Jupiter's orbit. At the latter the two families of Trojan asteroids can be found, which, at least for objects larger than 1 km, are approximately as numerous as the asteroids of the asteroid belt.
New families
Some asteroid families have formed recently, in astronomical terms. The Karin family apparently formed about 5.7 million years ago from a collision with a progenitor asteroid 33 km in radius. The Veritas family formed about 8.3 million years ago; evidence includes interplanetary dust recovered from ocean sediment.
More recently, the Datura cluster appears to have formed about 530,000 years ago from a collision with a main-belt asteroid. The age estimate is based on the probability of the members having their current orbits, rather than from any physical evidence. However, this cluster may have been a source for some zodiacal dust material. Other recent cluster formations, such as the Iannini cluster ( million years ago), may have provided additional sources of this asteroid dust.
Exploration
The first spacecraft to traverse the asteroid belt was Pioneer 10, which entered the region on 16 July 1972. At the time there was some concern that the debris in the belt would pose a hazard to the spacecraft, but it has since been safely traversed by multiple spacecraft without incident. Pioneer 11, Voyagers 1 and 2 and Ulysses passed through the belt without imaging any asteroids. Cassini measured plasma and fine dust grains while traversing the belt in 2000. On its way to Jupiter, Juno traversed the asteroid belt without collecting science data. Due to the low density of materials within the belt, the odds of a probe running into an asteroid are estimated at less than 1 in 1 billion. | Asteroid belt | Wikipedia | 474 | 47264 | https://en.wikipedia.org/wiki/Asteroid%20belt | Physical sciences | Solar System | null |
Most main belt asteroids imaged to date have come from brief flyby opportunities by probes headed for other targets. Only the Dawn mission has studied main belt asteroids for a protracted period in orbit. The Galileo spacecraft imaged 951 Gaspra in 1991 and 243 Ida in 1993, then NEAR imaged 253 Mathilde in 1997 and landed on near–Earth asteroid 433 Eros in February 2001. Cassini imaged 2685 Masursky in 2000, Stardust imaged 5535 Annefrank in 2002, New Horizons imaged 132524 APL in 2006, and Rosetta imaged 2867 Šteins in September 2008 and 21 Lutetia in July 2010. Dawn orbited Vesta between July 2011 and September 2012 and has orbited Ceres since March 2015.
The Lucy space probe made a flyby of 152830 Dinkinesh in 2023, on its way to the Jupiter Trojans. ESA's JUICE mission will pass through the asteroid belt twice, with a proposed flyby of the asteroid 223 Rosa in 2029. The Psyche'' spacecraft is a NASA mission to the large M-type asteroid 16 Psyche. | Asteroid belt | Wikipedia | 233 | 47264 | https://en.wikipedia.org/wiki/Asteroid%20belt | Physical sciences | Solar System | null |
Sponges or sea sponges are primarily marine invertebrates of the metazoan phylum Porifera ( ; meaning 'pore bearer'), a basal animal clade and a sister taxon of the diploblasts. They are sessile filter feeders that are bound to the seabed, and are one of the most ancient members of macrobenthos, with many historical species being important reef-building organisms.
Sponges are multicellular organisms consisting of jelly-like mesohyl sandwiched between two thin layers of cells, and usually have tube-like bodies full of pores and channels that allow water to circulate through them. They have unspecialized cells that can transform into other types and that often migrate between the main cell layers and the mesohyl in the process. They do not have complex nervous, digestive or circulatory systems. Instead, most rely on maintaining a constant water flow through their bodies to obtain food and oxygen and to remove wastes, usually via flagella movements of the so-called "collar cells".
Believed to be some of the most basal animals alive today, sponges were possibly the first outgroup to branch off the evolutionary tree from the last common ancestor of all animals, with fossil evidence of primitive sponges such as Otavia from as early as the Tonian period (around 800 Mya). The branch of zoology that studies sponges is known as spongiology.
Etymology
The term sponge derives from the Ancient Greek word . The scientific name Porifera is a neuter plural of the Modern Latin term porifer, which comes from the roots porus meaning "pore, opening", and -fer meaning "bearing or carrying".
Overview | Sponge | Wikipedia | 353 | 47271 | https://en.wikipedia.org/wiki/Sponge | Biology and health sciences | Porifera | null |
Sponges are similar to other animals in that they are multicellular, heterotrophic, lack cell walls and produce sperm cells. Unlike other animals, they lack true tissues and organs. Some of them are radially symmetrical, but most are asymmetrical. The shapes of their bodies are adapted for maximal efficiency of water flow through the central cavity, where the water deposits nutrients and then leaves through a hole called the osculum. The single-celled choanoflagellates resemble the choanocyte cells of sponges which are used to drive their water flow systems and capture most of their food. This along with phylogenetic studies of ribosomal molecules have been used as morphological evidence to suggest sponges are the sister group to the rest of animals. A great majority are marine (salt-water) species, ranging in habitat from tidal zones to depths exceeding , though there are freshwater species. All adult sponges are sessile, meaning that they attach to an underwater surface and remain fixed in place (i.e., do not travel). While in their larval stage of life, they are motile.
Many sponges have internal skeletons of spicules (skeletal-like fragments of calcium carbonate or silicon dioxide), and/or spongin (a modified type of collagen protein). An internal gelatinous matrix called mesohyl functions as an endoskeleton, and it is the only skeleton in soft sponges that encrust such hard surfaces as rocks. More commonly, the mesohyl is stiffened by mineral spicules, by spongin fibers, or both. 90% of all known sponge species that have the widest range of habitats including all freshwater ones are demosponges that use spongin; many species have silica spicules, whereas some species have calcium carbonate exoskeletons. Calcareous sponges have calcium carbonate spicules and, in some species, calcium carbonate exoskeletons, are restricted to relatively shallow marine waters where production of calcium carbonate is easiest. The fragile glass sponges, with "scaffolding" of silica spicules, are restricted to polar regions and the ocean depths where predators are rare. Fossils of all of these types have been found in rocks dated from . In addition Archaeocyathids, whose fossils are common in rocks from , are now regarded as a type of sponge. | Sponge | Wikipedia | 496 | 47271 | https://en.wikipedia.org/wiki/Sponge | Biology and health sciences | Porifera | null |
Although most of the approximately 5,000–10,000 known species of sponges feed on bacteria and other microscopic food in the water, some host photosynthesizing microorganisms as endosymbionts, and these alliances often produce more food and oxygen than they consume. A few species of sponges that live in food-poor environments have evolved as carnivores that prey mainly on small crustaceans.
Most sponges reproduce sexually, but they can also reproduce asexually. Sexually reproducing species release sperm cells into the water to fertilize ova released or retained by its mate or "mother"; the fertilized eggs develop into larvae which swim off in search of places to settle. Sponges are known for regenerating from fragments that are broken off, although this only works if the fragments include the right types of cells. Some species reproduce by budding. When environmental conditions become less hospitable to the sponges, for example as temperatures drop, many freshwater species and a few marine ones produce gemmules, "survival pods" of unspecialized cells that remain dormant until conditions improve; they then either form completely new sponges or recolonize the skeletons of their parents.
The few species of demosponge that have entirely soft fibrous skeletons with no hard elements have been used by humans over thousands of years for several purposes, including as padding and as cleaning tools. By the 1950s, though, these had been overfished so heavily that the industry almost collapsed, and most sponge-like materials are now synthetic. Sponges and their microscopic endosymbionts are now being researched as possible sources of medicines for treating a wide range of diseases. Dolphins have been observed using sponges as tools while foraging.
Distinguishing features
Sponges constitute the phylum Porifera, and have been defined as sessile metazoans (multicelled immobile animals) that have water intake and outlet openings connected by chambers lined with choanocytes, cells with whip-like flagella. However, a few carnivorous sponges have lost these water flow systems and the choanocytes. All known living sponges can remold their bodies, as most types of their cells can move within their bodies and a few can change from one type to another. | Sponge | Wikipedia | 476 | 47271 | https://en.wikipedia.org/wiki/Sponge | Biology and health sciences | Porifera | null |
Even if a few sponges are able to produce mucus – which acts as a microbial barrier in all other animals – no sponge with the ability to secrete a functional mucus layer has been recorded. Without such a mucus layer their living tissue is covered by a layer of microbial symbionts, which can contribute up to 40–50% of the sponge wet mass. This inability to prevent microbes from penetrating their porous tissue could be a major reason why they have never evolved a more complex anatomy.
Like cnidarians (jellyfish, etc.) and ctenophores (comb jellies), and unlike all other known metazoans, sponges' bodies consist of a non-living jelly-like mass (mesohyl) sandwiched between two main layers of cells. Cnidarians and ctenophores have simple nervous systems, and their cell layers are bound by internal connections and by being mounted on a basement membrane (thin fibrous mat, also known as "basal lamina"). Sponges do not have a nervous system similar to that of vertebrates but may have one that is quite different. Their middle jelly-like layers have large and varied populations of cells, and some types of cells in their outer layers may move into the middle layer and change their functions.
Basic structure
Cell types
A sponge's body is hollow and is held in shape by the mesohyl, a jelly-like substance made mainly of collagen and reinforced by a dense network of fibers also made of collagen. 18 distinct cell types have been identified. The inner surface is covered with choanocytes, cells with cylindrical or conical collars surrounding one flagellum per choanocyte. The wave-like motion of the whip-like flagella drives water through the sponge's body. All sponges have ostia, channels leading to the interior through the mesohyl, and in most sponges these are controlled by tube-like porocytes that form closable inlet valves. Pinacocytes, plate-like cells, form a single-layered external skin over all other parts of the mesohyl that are not covered by choanocytes, and the pinacocytes also digest food particles that are too large to enter the ostia, while those at the base of the animal are responsible for anchoring it.
Other types of cells live and move within the mesohyl: | Sponge | Wikipedia | 497 | 47271 | https://en.wikipedia.org/wiki/Sponge | Biology and health sciences | Porifera | null |
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