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Atlas Autocode
When AA was ported to the English Electric KDF9 computer, the character set was changed to International Organization for Standardization (ISO) and that compiler has been recovered from an old paper tape by the Edinburgh Computer History Project and is available online, as is a high-quality scan of the original Edinburgh version of the Atlas Autocode manual.
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Atlas Autocode
Keywords in AA were distinguishable from other text by being underlined, which was implemented via overstrike in the Flexowriter (compare to bold in ALGOL). There were also two stropping regimes. First, there was an "uppercasedelimiters" mode where all uppercase letters (outside strings) were treated as underlined lowercase. Second, in some versions (but not in the original Atlas version), it was possible to strop keywords by placing a "%" sign in front of them, for example the keyword endofprogramme could be typed as %end %of %programme or %endofprogramme. This significantly reduced typing, due to only needing one character, rather than overstriking the whole keyword. As in ALGOL, there were no reserved words in the language as keywords were identified by underlining (or stropping), not by recognising reserved character sequences. In the statement if token=if then result = token, there is both a keyword if and a variable named if.
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Atlas Autocode
As in ALGOL, AA allowed spaces in variable names, such as integer previous value. Spaces were not significant and were removed before parsing in a trivial pre-lexing stage called "line reconstruction". What the compiler would see in the above example would be "iftoken=ifthenresult=token". Spaces were possible due partly to keywords being distinguished in other ways, and partly because the source was processed by scannerless parsing, without a separate lexing phase, which allowed the lexical syntax to be context-sensitive.
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Atlas Autocode
The syntax for expressions let the multiplication operator be omitted, e.g., 3a was treated as 3*a, and a(i+j) was treated as a*(i+j) if a was not an array. In ambiguous uses, the longest possible name was taken (maximal munch), for example ab was not treated as a*b, whether or not a and b had been declared. In the original Atlas Autocode for the Atlas computer, Atlas machine code instructions could be interpolated between the AA statements. References Ferranti History of computing in the United Kingdom Structured programming languages
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Annals of Mathematics
The Annals of Mathematics is a mathematical journal published every two months by Princeton University and the Institute for Advanced Study. History
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Annals of Mathematics
The journal was established as The Analyst in 1874 and with Joel E. Hendricks as the founding editor-in-chief. It was "intended to afford a medium for the presentation and analysis of any and all questions of interest or importance in pure and applied Mathematics, embracing especially all new and interesting discoveries in theoretical and practical astronomy, mechanical philosophy, and engineering". It was published in Des Moines, Iowa, and was the earliest American mathematics journal to be published continuously for more than a year or two. This incarnation of the journal ceased publication after its tenth year, in 1883, giving as an explanation Hendricks' declining health, but Hendricks made arrangements to have it taken over by new management, and it was continued from March 1884 as the Annals of Mathematics. The new incarnation of the journal was edited by Ormond Stone (University of Virginia). It moved to Harvard in 1899 before reaching its current home in Princeton in 1911.
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Annals of Mathematics
An important period for the journal was 1928–1958 with Solomon Lefschetz as editor. During this time, it became an increasingly well-known and respected journal. Its rise, in turn, stimulated American mathematics. Norman Steenrod characterized Lefschetz' impact as editor as follows: "The importance to American mathematicians of a first-class journal is that it sets high standards for them to aim at. In this somewhat indirect manner, Lefschetz profoundly affected the development of mathematics in the United States."
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Annals of Mathematics
Princeton University continued to publish the Annals on its own until 1933, when the Institute for Advanced Study took joint editorial control. Since 1998 it has been available in an electronic edition, alongside its regular print edition. The electronic edition was available without charge, as an open access journal, but since 2008 this is no longer the case. Issues from before 2003 were transferred to the non-free JSTOR archive, and articles are not freely available until 5 years after publication.
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Annals of Mathematics
Editors The current editors of the Annals of Mathematics are Nick Katz, Sergiu Klainerman, Fernando Codá Marques, Assaf Naor, Peter Sarnak and Zoltán Szabó (all from Princeton University, with Peter Sarnak being also a Professor at the Institute for Advanced Study).
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Annals of Mathematics
Abstracting and indexing The journal is abstracted and indexed in the Science Citation Index, Current Contents/Physical, Chemical & Earth Sciences, and Scopus. According to the Journal Citation Reports, the journal has a 2020 impact factor of 5.246, ranking it third out of 330 journals in the category "Mathematics". References External links Mathematics journals Publications established in 1874 English-language journals Bimonthly journals Princeton University publications Academic journals published by universities and colleges of the United States 1874 establishments in Iowa
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Astrobiology
Astrobiology, known as exobiology, is an interdisciplinary scientific field that studies the origins, early evolution, distribution, and future of life in the universe. Astrobiology is the multidisciplinary field that investigates the deterministic conditions and contingent events with which life arises, distributes, and evolves in the universe. It considers the question of whether extraterrestrial life exists, and if it does, how humans can detect it.
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Astrobiology
Astrobiology makes use of molecular biology, biophysics, biochemistry, chemistry, astronomy, physical cosmology, exoplanetology, geology, paleontology, and ichnology to investigate the possibility of life on other worlds and help recognize biospheres that might be different from that on Earth. The origin and early evolution of life is an inseparable part of the discipline of astrobiology. Astrobiology concerns itself with interpretation of existing scientific data, and although speculation is entertained to give context, astrobiology concerns itself primarily with hypotheses that fit firmly into existing scientific theories.
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Astrobiology
This interdisciplinary field encompasses research on the origin of planetary systems, origins of organic compounds in space, rock-water-carbon interactions, abiogenesis on Earth, planetary habitability, research on biosignatures for life detection, and studies on the potential for life to adapt to challenges on Earth and in outer space.
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Astrobiology
Biochemistry may have begun shortly after the Big Bang, 13.8 billion years ago, during a habitable epoch when the Universe was only 10–17 million years old. According to the panspermia hypothesis, microscopic life—distributed by meteoroids, asteroids and other small Solar System bodies—may exist throughout the universe. According to research published in August 2015, very large galaxies may be more favorable to the creation and development of habitable planets than such smaller galaxies as the Milky Way. Nonetheless, Earth is the only place in the universe humans know to harbor life. Estimates of habitable zones around other stars, sometimes referred to as "Goldilocks zones", along with the discovery of thousands of extrasolar planets and new insights into extreme habitats here on Earth, suggest that there may be many more habitable places in the universe than considered possible until very recently.
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Astrobiology
Current studies on the planet Mars by the Curiosity and Perseverance rovers are searching for evidence of ancient life as well as plains related to ancient rivers or lakes that may have been habitable. The search for evidence of habitability, taphonomy (related to fossils), and organic molecules on the planet Mars is now a primary NASA and ESA objective. Even if extraterrestrial life is never discovered, the interdisciplinary nature of astrobiology, and the cosmic and evolutionary perspectives engendered by it, may still result in a range of benefits here on Earth.
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Astrobiology
Overview The term was first proposed by the Russian (Soviet) astronomer Gavriil Tikhov in 1953. Astrobiology is etymologically derived from the Greek , astron, "constellation, star"; , bios, "life"; and , -logia, study. The synonyms of astrobiology are diverse; however, the synonyms were structured in relation to the most important sciences implied in its development: astronomy and biology. A close synonym is exobiology from the Greek , "external"; Βίος, bios, "life"; and λογία, -logia, study. The term exobiology was coined by molecular biologist and Nobel Prize winner Joshua Lederberg. Exobiology is considered to have a narrow scope limited to search of life external to Earth, whereas subject area of astrobiology is wider and investigates the link between life and the universe, which includes the search for extraterrestrial life, but also includes the study of life on Earth, its origin, evolution and limits.
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Astrobiology
Another term used in the past is xenobiology, ("biology of the foreigners") a word used in 1954 by science fiction writer Robert Heinlein in his work The Star Beast. The term xenobiology is now used in a more specialized sense, to mean "biology based on foreign chemistry", whether of extraterrestrial or terrestrial (possibly synthetic) origin. Since alternate chemistry analogs to some life-processes have been created in the laboratory, xenobiology is now considered as an extant subject.
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Astrobiology
While it is an emerging and developing field, the question of whether life exists elsewhere in the universe is a verifiable hypothesis and thus a valid line of scientific inquiry. Though once considered outside the mainstream of scientific inquiry, astrobiology has become a formalized field of study. Planetary scientist David Grinspoon calls astrobiology a field of natural philosophy, grounding speculation on the unknown, in known scientific theory. NASA's interest in exobiology first began with the development of the U.S. Space Program. In 1959, NASA funded its first exobiology project, and in 1960, NASA founded an Exobiology Program, which is now one of four main elements of NASA's current Astrobiology Program. In 1971, NASA funded the search for extraterrestrial intelligence (SETI) to search radio frequencies of the electromagnetic spectrum for interstellar communications transmitted by extraterrestrial life outside the Solar System. NASA's Viking missions to Mars, launched in 1976, included three biology experiments designed to look for metabolism of present life on Mars.
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Astrobiology
Advancements in the fields of astrobiology, observational astronomy and discovery of large varieties of extremophiles with extraordinary capability to thrive in the harshest environments on Earth, have led to speculation that life may possibly be thriving on many of the extraterrestrial bodies in the universe. A particular focus of current astrobiology research is the search for life on Mars due to this planet's proximity to Earth and geological history. There is a growing body of evidence to suggest that Mars has previously had a considerable amount of water on its surface, water being considered an essential precursor to the development of carbon-based life.
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Astrobiology
Missions specifically designed to search for current life on Mars were the Viking program and Beagle 2 probes. The Viking results were inconclusive, and Beagle 2 failed minutes after landing. A future mission with a strong astrobiology role would have been the Jupiter Icy Moons Orbiter, designed to study the frozen moons of Jupiter—some of which may have liquid water—had it not been cancelled. In late 2008, the Phoenix lander probed the environment for past and present planetary habitability of microbial life on Mars, and researched the history of water there.
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Astrobiology
The European Space Agency's astrobiology roadmap from 2016, identified five main research topics, and specifies several key scientific objectives for each topic. The five research topics are: 1) Origin and evolution of planetary systems; 2) Origins of organic compounds in space; 3) Rock-water-carbon interactions, organic synthesis on Earth, and steps to life; 4) Life and habitability; 5) Biosignatures as facilitating life detection.
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In November 2011, NASA launched the Mars Science Laboratory mission carrying the Curiosity rover, which landed on Mars at Gale Crater in August 2012. The Curiosity rover is currently probing the environment for past and present planetary habitability of microbial life on Mars. On 9 December 2013, NASA reported that, based on evidence from Curiosity studying Aeolis Palus, Gale Crater contained an ancient freshwater lake which could have been a hospitable environment for microbial life.
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The European Space Agency is currently collaborating with the Russian Federal Space Agency (Roscosmos) and developing the ExoMars astrobiology rover, which was scheduled to be launched in July 2020, but was postponed to 2022. Meanwhile, NASA launched the Mars 2020 astrobiology rover and sample cacher for a later return to Earth. Methodology Planetary habitability
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Astrobiology
When looking for life on other planets like Earth, some simplifying assumptions are useful to reduce the size of the task of the astrobiologist. One is the informed assumption that the vast majority of life forms in our galaxy are based on carbon chemistries, as are all life forms on Earth. Carbon is well known for the unusually wide variety of molecules that can be formed around it. Carbon is the fourth most abundant element in the universe and the energy required to make or break a bond is at just the appropriate level for building molecules which are not only stable, but also reactive. The fact that carbon atoms bond readily to other carbon atoms allows for the building of extremely long and complex molecules.
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The presence of liquid water is an assumed requirement, as it is a common molecule and provides an excellent environment for the formation of complicated carbon-based molecules that could eventually lead to the emergence of life. Some researchers posit environments of water-ammonia mixtures as possible solvents for hypothetical types of biochemistry.
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A third assumption is to focus on planets orbiting Sun-like stars for increased probabilities of planetary habitability. Very large stars have relatively short lifetimes, meaning that life might not have time to emerge on planets orbiting them. Very small stars provide so little heat and warmth that only planets in very close orbits around them would not be frozen solid, and in such close orbits these planets would be tidally "locked" to the star. The long lifetimes of red dwarfs could allow the development of habitable environments on planets with thick atmospheres. This is significant, as red dwarfs are extremely common. (See Habitability of red dwarf systems).
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Since Earth is the only planet known to harbor life, there is no evident way to know if any of these simplifying assumptions are correct. Communication attempts Research on communication with extraterrestrial intelligence (CETI) focuses on composing and deciphering messages that could theoretically be understood by another technological civilization. Communication attempts by humans have included broadcasting mathematical languages, pictorial systems such as the Arecibo message and computational approaches to detecting and deciphering 'natural' language communication. The SETI program, for example, uses both radio telescopes and optical telescopes to search for deliberate signals from an extraterrestrial intelligence.
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While some high-profile scientists, such as Carl Sagan, have advocated the transmission of messages, scientist Stephen Hawking warned against it, suggesting that aliens might simply raid Earth for its resources and then move on. Elements of astrobiology Astronomy
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Astrobiology
Most astronomy-related astrobiology research falls into the category of extrasolar planet (exoplanet) detection, the hypothesis being that if life arose on Earth, then it could also arise on other planets with similar characteristics. To that end, a number of instruments designed to detect Earth-sized exoplanets have been considered, most notably NASA's Terrestrial Planet Finder (TPF) and ESA's Darwin programs, both of which have been cancelled. NASA launched the Kepler mission in March 2009, and the French Space Agency launched the COROT space mission in 2006. There are also several less ambitious ground-based efforts underway.
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Astrobiology
The goal of these missions is not only to detect Earth-sized planets but also to directly detect light from the planet so that it may be studied spectroscopically. By examining planetary spectra, it would be possible to determine the basic composition of an extrasolar planet's atmosphere and/or surface. Given this knowledge, it may be possible to assess the likelihood of life being found on that planet. A NASA research group, the Virtual Planet Laboratory, is using computer modeling to generate a wide variety of virtual planets to see what they would look like if viewed by TPF or Darwin. It is hoped that once these missions come online, their spectra can be cross-checked with these virtual planetary spectra for features that might indicate the presence of life.
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An estimate for the number of planets with intelligent communicative extraterrestrial life can be gleaned from the Drake equation, essentially an equation expressing the probability of intelligent life as the product of factors such as the fraction of planets that might be habitable and the fraction of planets on which life might arise:
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Astrobiology
where: N = The number of communicative civilizations R* = The rate of formation of suitable stars (stars such as our Sun) fp = The fraction of those stars with planets (current evidence indicates that planetary systems may be common for stars like the Sun) ne = The number of Earth-sized worlds per planetary system fl = The fraction of those Earth-sized planets where life actually develops fi = The fraction of life sites where intelligence develops fc = The fraction of communicative planets (those on which electromagnetic communications technology develops) L = The "lifetime" of communicating civilizations
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However, whilst the rationale behind the equation is sound, it is unlikely that the equation will be constrained to reasonable limits of error any time soon. The problem with the formula is that it is not used to generate or support hypotheses because it contains factors that can never be verified. The first term, R*, number of stars, is generally constrained within a few orders of magnitude. The second and third terms, fp, stars with planets and fe, planets with habitable conditions, are being evaluated for the star's neighborhood. Drake originally formulated the equation merely as an agenda for discussion at the Green Bank conference, but some applications of the formula had been taken literally and related to simplistic or pseudoscientific arguments. Another associated topic is the Fermi paradox, which suggests that if intelligent life is common in the universe, then there should be obvious signs of it.
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Astrobiology
Another active research area in astrobiology is planetary system formation. It has been suggested that the peculiarities of the Solar System (for example, the presence of Jupiter as a protective shield) may have greatly increased the probability of intelligent life arising on our planet. Biology
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Biology cannot state that a process or phenomenon, by being mathematically possible, has to exist forcibly in an extraterrestrial body. Biologists specify what is speculative and what is not. The discovery of extremophiles, organisms able to survive in extreme environments, became a core research element for astrobiologists, as they are important to understand four areas in the limits of life in planetary context: the potential for panspermia, forward contamination due to human exploration ventures, planetary colonization by humans, and the exploration of extinct and extant extraterrestrial life.
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Until the 1970s, life was thought to be entirely dependent on energy from the Sun. Plants on Earth's surface capture energy from sunlight to photosynthesize sugars from carbon dioxide and water, releasing oxygen in the process that is then consumed by oxygen-respiring organisms, passing their energy up the food chain. Even life in the ocean depths, where sunlight cannot reach, was thought to obtain its nourishment either from consuming organic detritus rained down from the surface waters or from eating animals that did. The world's ability to support life was thought to depend on its access to sunlight. However, in 1977, during an exploratory dive to the Galapagos Rift in the deep-sea exploration submersible Alvin, scientists discovered colonies of giant tube worms, clams, crustaceans, mussels, and other assorted creatures clustered around undersea volcanic features known as black smokers. These creatures thrive despite having no access to sunlight, and it was soon discovered that they comprise an entirely independent ecosystem. Although most of these multicellular lifeforms need dissolved oxygen (produced by oxygenic photosynthesis) for their aerobic cellular respiration and thus are not completely independent from sunlight by themselves, the basis for their food chain is a form of bacterium that derives its energy from oxidization of reactive chemicals, such as hydrogen or hydrogen sulfide, that bubble up from the Earth's interior. Other lifeforms entirely decoupled from the energy from sunlight are green sulfur bacteria which are capturing geothermal light for anoxygenic photosynthesis or bacteria running chemolithoautotrophy based on the radioactive decay of uranium. This chemosynthesis revolutionized the study of biology and astrobiology by revealing that life need not be sun-dependent; it only requires water and an energy gradient in order to exist.
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Biologists have found extremophiles that thrive in ice, boiling water, acid, alkali, the water core of nuclear reactors, salt crystals, toxic waste and in a range of other extreme habitats that were previously thought to be inhospitable for life. This opened up a new avenue in astrobiology by massively expanding the number of possible extraterrestrial habitats. Characterization of these organisms, their environments and their evolutionary pathways, is considered a crucial component to understanding how life might evolve elsewhere in the universe. For example, some organisms able to withstand exposure to the vacuum and radiation of outer space include the lichen fungi Rhizocarpon geographicum and Xanthoria elegans, the bacterium Bacillus safensis, Deinococcus radiodurans, Bacillus subtilis, yeast Saccharomyces cerevisiae, seeds from Arabidopsis thaliana ('mouse-ear cress'), as well as the invertebrate animal Tardigrade. While tardigrades are not considered true extremophiles, they are considered extremotolerant microorganisms that have contributed to the field of astrobiology. Their extreme radiation tolerance and presence of DNA protection proteins may provide answers as to whether life can survive away from the protection of the Earth's atmosphere.
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Astrobiology
Jupiter's moon, Europa, and Saturn's moon, Enceladus, are now considered the most likely locations for extant extraterrestrial life in the Solar System due to their subsurface water oceans where radiogenic and tidal heating enables liquid water to exist.
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The origin of life, known as abiogenesis, distinct from the evolution of life, is another ongoing field of research. Oparin and Haldane postulated that the conditions on the early Earth were conducive to the formation of organic compounds from inorganic elements and thus to the formation of many of the chemicals common to all forms of life we see today. The study of this process, known as prebiotic chemistry, has made some progress, but it is still unclear whether or not life could have formed in such a manner on Earth. The alternative hypothesis of panspermia is that the first elements of life may have formed on another planet with even more favorable conditions (or even in interstellar space, asteroids, etc.) and then have been carried over to Earth.
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The cosmic dust permeating the universe contains complex organic compounds ("amorphous organic solids with a mixed aromatic-aliphatic structure") that could be created naturally, and rapidly, by stars. Further, a scientist suggested that these compounds may have been related to the development of life on Earth and said that, "If this is the case, life on Earth may have had an easier time getting started as these organics can serve as basic ingredients for life."
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More than 20% of the carbon in the universe may be associated with polycyclic aromatic hydrocarbons (PAHs), possible starting materials for the formation of life. PAHs seem to have been formed shortly after the Big Bang, are widespread throughout the universe, and are associated with new stars and exoplanets. PAHs are subjected to interstellar medium conditions and are transformed through hydrogenation, oxygenation and hydroxylation, to more complex organics—"a step along the path toward amino acids and nucleotides, the raw materials of proteins and DNA, respectively".
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In October 2020, astronomers proposed the idea of detecting life on distant planets by studying the shadows of trees at certain times of the day to find patterns that could be detected through observation of exoplanets. Astroecology Astroecology concerns the interactions of life with space environments and resources, in planets, asteroids and comets. On a larger scale, astroecology concerns resources for life about stars in the galaxy through the cosmological future. Astroecology attempts to quantify future life in space, addressing this area of astrobiology.
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Experimental astroecology investigates resources in planetary soils, using actual space materials in meteorites. The results suggest that Martian and carbonaceous chondrite materials can support bacteria, algae and plant (asparagus, potato) cultures, with high soil fertilities. The results support that life could have survived in early aqueous asteroids and on similar materials imported to Earth by dust, comets and meteorites, and that such asteroid materials can be used as soil for future space colonies.
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On the largest scale, cosmoecology concerns life in the universe over cosmological times. The main sources of energy may be red giant stars and white and red dwarf stars, sustaining life for 1020 years. Astroecologists suggest that their mathematical models may quantify the potential amounts of future life in space, allowing a comparable expansion in biodiversity, potentially leading to diverse intelligent life forms. Astrogeology
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Astrogeology is a planetary science discipline concerned with the geology of celestial bodies such as the planets and their moons, asteroids, comets, and meteorites. The information gathered by this discipline allows the measure of a planet's or a natural satellite's potential to develop and sustain life, or planetary habitability.
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An additional discipline of astrogeology is geochemistry, which involves study of the chemical composition of the Earth and other planets, chemical processes and reactions that govern the composition of rocks and soils, the cycles of matter and energy and their interaction with the hydrosphere and the atmosphere of the planet. Specializations include cosmochemistry, biochemistry and organic geochemistry.
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The fossil record provides the oldest known evidence for life on Earth. By examining the fossil evidence, paleontologists are able to better understand the types of organisms that arose on the early Earth. Some regions on Earth, such as the Pilbara in Western Australia and the McMurdo Dry Valleys of Antarctica, are also considered to be geological analogs to regions of Mars, and as such, might be able to provide clues on how to search for past life on Mars.
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The various organic functional groups, composed of hydrogen, oxygen, nitrogen, phosphorus, sulfur, and a host of metals, such as iron, magnesium, and zinc, provide the enormous diversity of chemical reactions necessarily catalyzed by a living organism. Silicon, in contrast, interacts with only a few other atoms, and the large silicon molecules are monotonous compared with the combinatorial universe of organic macromolecules. Indeed, it seems likely that the basic building blocks of life anywhere will be similar to those on Earth, in the generality if not in the detail. Although terrestrial life and life that might arise independently of Earth are expected to use many similar, if not identical, building blocks, they also are expected to have some biochemical qualities that are unique. If life has had a comparable impact elsewhere in the Solar System, the relative abundances of chemicals key for its survival—whatever they may be—could betray its presence. Whatever extraterrestrial life may be, its tendency to chemically alter its environment might just give it away.
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Life in the Solar System
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People have long speculated about the possibility of life in settings other than Earth, however, speculation on the nature of life elsewhere often has paid little heed to constraints imposed by the nature of biochemistry. The likelihood that life throughout the universe is probably carbon-based is suggested by the fact that carbon is one of the most abundant of the higher elements. Only two of the natural atoms, carbon and silicon, are known to serve as the backbones of molecules sufficiently large to carry biological information. As the structural basis for life, one of carbon's important features is that, unlike silicon, it can readily engage in the formation of chemical bonds with many other atoms, thereby allowing for the chemical versatility required to conduct the reactions of biological metabolism and propagation.
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Discussion on where in the Solar System life might occur was limited historically by the understanding that life relies ultimately on light and warmth from the Sun and, therefore, is restricted to the surfaces of planets. The four most likely candidates for life in the Solar System are the planet Mars, the Jovian moon Europa, and Saturn's moons Titan and Enceladus.
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Mars, Enceladus and Europa are considered likely candidates in the search for life primarily because they may have underground liquid water, a molecule essential for life as we know it for its use as a solvent in cells. Water on Mars is found frozen in its polar ice caps, and newly carved gullies recently observed on Mars suggest that liquid water may exist, at least transiently, on the planet's surface. At the Martian low temperatures and low pressure, liquid water is likely to be highly saline. As for Europa and Enceladus, large global oceans of liquid water exist beneath these moons' icy outer crusts. This water may be warmed to a liquid state by volcanic vents on the ocean floor, but the primary source of heat is probably tidal heating. On 11 December 2013, NASA reported the detection of "clay-like minerals" (specifically, phyllosilicates), often associated with organic materials, on the icy crust of Europa. The presence of the minerals may have been the result of a collision with an asteroid or comet according to the scientists. Additionally, on 27 June 2018, astronomers reported the detection of complex macromolecular organics on Enceladus and, according to NASA scientists in May 2011, "is emerging as the most habitable spot beyond Earth in the Solar System for life as we know it".
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Another planetary body that could potentially sustain extraterrestrial life is Saturn's largest moon, Titan. Titan has been described as having conditions similar to those of early Earth. On its surface, scientists have discovered the first liquid lakes outside Earth, but these lakes seem to be composed of ethane and/or methane, not water. Some scientists think it possible that these liquid hydrocarbons might take the place of water in living cells different from those on Earth. After Cassini data were studied, it was reported in March 2008 that Titan may also have an underground ocean composed of liquid water and ammonia.
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Phosphine has been detected in the atmosphere of the planet Venus. There are no known abiotic processes on the planet that could cause its presence. Given that Venus has the hottest surface temperature of any planet in the solar system, Venusian life, if it exists, is most likely limited to extremophile microorganisms that float in the planet's upper atmosphere, where conditions are almost Earth-like.
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Measuring the ratio of hydrogen and methane levels on Mars may help determine the likelihood of life on Mars. According to the scientists, "...low H2/CH4 ratios (less than approximately 40) indicate that life is likely present and active." Other scientists have recently reported methods of detecting hydrogen and methane in extraterrestrial atmospheres.
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Complex organic compounds of life, including uracil, cytosine and thymine, have been formed in a laboratory under outer space conditions, using starting chemicals such as pyrimidine, found in meteorites. Pyrimidine, like polycyclic aromatic hydrocarbons (PAHs), is the most carbon-rich chemical found in the universe. Rare Earth hypothesis
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The Rare Earth hypothesis postulates that multicellular life forms found on Earth may actually be more of a rarity than scientists assume. According to this hypothesis, life on Earth (and more, multi-cellular life) is possible because of a conjunction of the right circumstances (galaxy and location within it, solar system, star, orbit, planetary size, atmosphere, etc.); and the chance for all those circumstances to repeat elsewhere may be rare. It provides a possible answer to the Fermi paradox which suggests, "If extraterrestrial aliens are common, why aren't they obvious?" It is apparently in opposition to the principle of mediocrity, assumed by famed astronomers Frank Drake, Carl Sagan, and others. The Principle of Mediocrity suggests that life on Earth is not exceptional, and it is more than likely to be found on innumerable other worlds.
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Research The systematic search for possible life outside Earth is a valid multidisciplinary scientific endeavor. However, hypotheses and predictions as to its existence and origin vary widely, and at the present, the development of hypotheses firmly grounded on science may be considered astrobiology's most concrete practical application. It has been proposed that viruses are likely to be encountered on other life-bearing planets, and may be present even if there are no biological cells. Research outcomes
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, no evidence of extraterrestrial life has been identified. Examination of the Allan Hills 84001 meteorite, which was recovered in Antarctica in 1984 and originated from Mars, is thought by David McKay, as well as few other scientists, to contain microfossils of extraterrestrial origin; this interpretation is controversial.
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Yamato 000593, the second largest meteorite from Mars, was found on Earth in 2000. At a microscopic level, spheres are found in the meteorite that are rich in carbon compared to surrounding areas that lack such spheres. The carbon-rich spheres may have been formed by biotic activity according to some NASA scientists.
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On 5 March 2011, Richard B. Hoover, a scientist with the Marshall Space Flight Center, speculated on the finding of alleged microfossils similar to cyanobacteria in CI1 carbonaceous meteorites in the fringe Journal of Cosmology, a story widely reported on by mainstream media. However, NASA formally distanced itself from Hoover's claim. According to American astrophysicist Neil deGrasse Tyson: "At the moment, life on Earth is the only known life in the universe, but there are compelling arguments to suggest we are not alone." Extreme environments on Earth
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On 17 March 2013, researchers reported that microbial life forms thrive in the Mariana Trench, the deepest spot on the Earth. Other researchers reported that microbes thrive inside rocks up to below the sea floor under of ocean off the coast of the northwestern United States. According to one of the researchers, "You can find microbes everywhere—they're extremely adaptable to conditions, and survive wherever they are." Evidence of perchlorates have been found throughout the solar system, and specifically on Mars. Dr. Kennda Lynch discovered the first known instance of perchlorates and perchlorates-reducing microbes in a paleolake in Pilot Valley, Utah. These finds expand the potential habitability of certain niches of other planets.
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Methane In 2004, the spectral signature of methane () was detected in the Martian atmosphere by both Earth-based telescopes as well as by the Mars Express orbiter. Because of solar radiation and cosmic radiation, methane is predicted to disappear from the Martian atmosphere within several years, so the gas must be actively replenished in order to maintain the present concentration. On 7 June 2018, NASA announced a cyclical seasonal variation in atmospheric methane, which may be produced by geological or biological sources. The European ExoMars Trace Gas Orbiter is currently measuring and mapping the atmospheric methane.
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Planetary systems It is possible that some exoplanets may have moons with solid surfaces or liquid oceans that are hospitable. Most of the planets so far discovered outside the Solar System are hot gas giants thought to be inhospitable to life, so it is not yet known whether the Solar System, with a warm, rocky, metal-rich inner planet such as Earth, is of an aberrant composition. Improved detection methods and increased observation time will undoubtedly discover more planetary systems, and possibly some more like ours. For example, NASA's Kepler Mission seeks to discover Earth-sized planets around other stars by measuring minute changes in the star's light curve as the planet passes between the star and the spacecraft. Progress in infrared astronomy and submillimeter astronomy has revealed the constituents of other star systems.
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Planetary habitability Efforts to answer questions such as the abundance of potentially habitable planets in habitable zones and chemical precursors have had much success. Numerous extrasolar planets have been detected using the wobble method and transit method, showing that planets around other stars are more numerous than previously postulated. The first Earth-sized extrasolar planet to be discovered within its star's habitable zone is Gliese 581 c.
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Extremophiles Studying extremophiles is useful for understanding the possible origin of life on Earth as well as for finding the most likely candidates for future colonization of other planets. The aim is to detect those organisms that are able to survive space travel conditions and to maintain the proliferating capacity. The best candidates are extremophiles, since they have adapted to survive in different kind of extreme conditions on earth. During the course of evolution, extremophiles have developed various strategies to survive the different stress conditions of different extreme environments. These stress responses could also allow them to survive in harsh space conditions, although evolution also puts some restrictions on their use as analogues to extraterrestrial life.
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Thermophilic species G. thermantarcticus is a good example of a microorganism that could survive space travel. It is a bacterium of the spore-forming genus Bacillus. The formation of spores allows for it to survive extreme environments while still being able to restart cellular growth. It is capable of effectively protecting its DNA, membrane and proteins integrity in different extreme conditions (desiccation, temperatures up to -196 °C, UVC and C-ray radiation...). It is also able to repair the damage produced by space environment.
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Some locations on Earth are particularly well-suited for astrobiological studies of extremophiles. For example, Valeria Souza and colleagues proposed that the Cuatro Ciénegas basin in Coahuila, Mexico, could serve as an "astrobiological Precambrian park" due to the similarity of some of its ecosystems to an earlier time in Earth's history when multicellular life began to dominate.
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By understanding how extremophilic organisms can survive the Earth's extreme environments, we can also understand how microorganisms could have survived space travel and how the panspermia hypothesis could be possible. Missions Research into the environmental limits of life and the workings of extreme ecosystems is ongoing, enabling researchers to better predict what planetary environments might be most likely to harbor life. Missions such as the Phoenix lander, Mars Science Laboratory, ExoMars, Mars 2020 rover to Mars, and the Cassini probe to Saturn's moons aim to further explore the possibilities of life on other planets in the Solar System. Viking program
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The two Viking landers each carried four types of biological experiments to the surface of Mars in the late 1970s. These were the only Mars landers to carry out experiments looking specifically for metabolism by current microbial life on Mars. The landers used a robotic arm to collect soil samples into sealed test containers on the craft. The two landers were identical, so the same tests were carried out at two places on Mars' surface; Viking 1 near the equator and Viking 2 further north. The result was inconclusive, and is still disputed by some scientists. Norman Horowitz was the chief of the Jet Propulsion Laboratory bioscience section for the Mariner and Viking missions from 1965 to 1976. Horowitz considered that the great versatility of the carbon atom makes it the element most likely to provide solutions, even exotic solutions, to the problems of survival of life on other planets. However, he also considered that the conditions found on Mars were incompatible with carbon based life.
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Beagle 2 Beagle 2 was an unsuccessful British Mars lander that formed part of the European Space Agency's 2003 Mars Express mission. Its primary purpose was to search for signs of life on Mars, past or present. Although it landed safely, it was unable to correctly deploy its solar panels and telecom antenna. EXPOSE EXPOSE is a multi-user facility mounted in 2008 outside the International Space Station dedicated to astrobiology. EXPOSE was developed by the European Space Agency (ESA) for long-term spaceflights that allow exposure of organic chemicals and biological samples to outer space in low Earth orbit.
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Mars Science Laboratory The Mars Science Laboratory (MSL) mission landed the Curiosity rover that is currently in operation on Mars. It was launched 26 November 2011, and landed at Gale Crater on 6 August 2012. Mission objectives are to help assess Mars' habitability and in doing so, determine whether Mars is or has ever been able to support life, collect data for a future human mission, study Martian geology, its climate, and further assess the role that water, an essential ingredient for life as we know it, played in forming minerals on Mars.
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Tanpopo The Tanpopo mission is an orbital astrobiology experiment investigating the potential interplanetary transfer of life, organic compounds, and possible terrestrial particles in the low Earth orbit. The purpose is to assess the panspermia hypothesis and the possibility of natural interplanetary transport of microbial life as well as prebiotic organic compounds. Early mission results show evidence that some clumps of microorganism can survive for at least one year in space. This may support the idea that clumps greater than 0.5 millimeters of microorganisms could be one way for life to spread from planet to planet.
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ExoMars rover ExoMars is a robotic mission to Mars to search for possible biosignatures of Martian life, past or present. This astrobiological mission is currently under development by the European Space Agency (ESA) in partnership with the Russian Federal Space Agency (Roscosmos); it is planned for a 2022 launch. Mars 2020
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Mars 2020 successfully landed its rover Perseverance in Jezero Crater on 18 February 2021. It will investigate environments on Mars relevant to astrobiology, investigate its surface geological processes and history, including the assessment of its past habitability and potential for preservation of biosignatures and biomolecules within accessible geological materials. The Science Definition Team is proposing the rover collect and package at least 31 samples of rock cores and soil for a later mission to bring back for more definitive analysis in laboratories on Earth. The rover could make measurements and technology demonstrations to help designers of a human expedition understand any hazards posed by Martian dust and demonstrate how to collect carbon dioxide (CO2), which could be a resource for making molecular oxygen (O2) and rocket fuel.
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Europa Clipper Europa Clipper is a mission planned by NASA for a 2025 launch that will conduct detailed reconnaissance of Jupiter's moon Europa and will investigate whether its internal ocean could harbor conditions suitable for life. It will also aid in the selection of future landing sites. Proposed concepts
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Icebreaker Life Icebreaker Life is a lander mission that was proposed for NASA's Discovery Program for the 2021 launch opportunity, but it was not selected for development. It would have had a stationary lander that would be a near copy of the successful 2008 Phoenix and it would have carried an upgraded astrobiology scientific payload, including a 1-meter-long core drill to sample ice-cemented ground in the northern plains to conduct a search for organic molecules and evidence of current or past life on Mars. One of the key goals of the Icebreaker Life mission is to test the hypothesis that the ice-rich ground in the polar regions has significant concentrations of organics due to protection by the ice from oxidants and radiation.
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Journey to Enceladus and Titan Journey to Enceladus and Titan (JET) is an astrobiology mission concept to assess the habitability potential of Saturn's moons Enceladus and Titan by means of an orbiter. Enceladus Life Finder Enceladus Life Finder (ELF) is a proposed astrobiology mission concept for a space probe intended to assess the habitability of the internal aquatic ocean of Enceladus, Saturn's sixth-largest moon.
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Life Investigation For Enceladus Life Investigation For Enceladus (LIFE) is a proposed astrobiology sample-return mission concept. The spacecraft would enter into Saturn orbit and enable multiple flybys through Enceladus' icy plumes to collect icy plume particles and volatiles and return them to Earth on a capsule. The spacecraft may sample Enceladus' plumes, the E ring of Saturn, and the upper atmosphere of Titan.
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Oceanus Oceanus is an orbiter proposed in 2017 for the New Frontiers mission No. 4. It would travel to the moon of Saturn, Titan, to assess its habitability. Oceanus objectives are to reveal Titan's organic chemistry, geology, gravity, topography, collect 3D reconnaissance data, catalog the organics and determine where they may interact with liquid water.
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Explorer of Enceladus and Titan Explorer of Enceladus and Titan (E2T) is an orbiter mission concept that would investigate the evolution and habitability of the Saturnian satellites Enceladus and Titan. The mission concept was proposed in 2017 by the European Space Agency. See also Astrobiology.com Top ranked news source for Astrobiology The Living Cosmos References
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Bibliography The International Journal of Astrobiology, published by Cambridge University Press, is the forum for practitioners in this interdisciplinary field. Astrobiology, published by Mary Ann Liebert, Inc., is a peer-reviewed journal that explores the origins of life, evolution, distribution, and destiny in the universe. Loeb, Avi (2021). Extraterrestrial: The First Sign of Intelligent Life Beyond Earth. Houghton Mifflin Harcourt. Further reading D. Goldsmith, T. Owen, The Search For Life in the Universe, Addison-Wesley Publishing Company, 2001 (3rd edition).
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Andy Weir's best-selling 2021 novel, Project Hail Mary, centers on astrobiology. Dealing with climate change caused by space-dwelling microbes, an astronaut finds that another civilization is suffering from the same problem. External links Astrobiology.nasa.gov UK Centre for Astrobiology Spanish Centro de Astrobiología Astrobiology Research at The Library of Congress Astrobiology Magazine Exploring Solar System and Beyond Astrobiology Survey – An introductory course on astrobiology Summary - Search For Life Beyond Earth (NASA; 25 June 2021) Extraterrestrial life Origin of life Astronomical sub-disciplines Branches of biology Speculative evolution
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AIM (AOL Instant Messenger) was an instant messaging and presence computer program created by AOL, which used the proprietary OSCAR instant messaging protocol and the TOC protocol to allow registered users to communicate in real time.
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AIM was popular by the late 1990s, in United States and other countries, and was the leading instant messaging application in that region into the following decade. Teens and college students were known to use the messenger's away message feature to keep in touch with friends, often frequently changing their away message throughout a day or leaving a message up with one's computer left on to inform buddies of their ongoings, location, parties, thoughts, or jokes. AIM's popularity declined as AOL subscribers started decreasing and steeply towards the 2010s, as Gmail's Google Talk, SMS, and Internet social networks, like Facebook gained popularity. Its fall has often been compared with other once-popular Internet services, such as Myspace.
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In June 2015, AOL was acquired by Verizon Communications. In June 2017, Verizon combined AOL and Yahoo into its subsidiary Oath Inc. (now called Yahoo). The company discontinued AIM as a service on December 15, 2017.
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History In May 1997, AIM was released unceremoniously as a stand-alone download for Microsoft Windows. AIM was an outgrowth of "online messages" in the original platform written in PL/1 on a Stratus computer by Dave Brown. At one time, the software had the largest share of the instant messaging market in North America, especially in the United States (with 52% of the total reported ). This does not include other instant messaging software related to or developed by AOL, such as ICQ and iChat.
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During its heyday, its main competitors were ICQ (although AOL acquired ICQ in 1998), Yahoo! Messenger and MSN Messenger. AOL particularly had a rivalry or "chat war" with PowWow and Microsoft, starting in 1999. There were several attempts from Microsoft to simultaneously log into their own and AIM's protocol servers. AOL was not happy about this and started blocking MSN Messenger from being able to access AIM. This led to efforts by many companies to challenge the AOL and Time Warner merger on the grounds of antitrust behaviour, leading to the formation of the OpenNet Coalition.
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Official mobile versions of AIM appeared as early as 2001 on Palm OS through the AOL application. Third-party applications allowed it to be used in 2002 for the Sidekick. A version for Symbian OS was announced in 2003 and others for BlackBerry and Windows Mobile After 2012, stand-alone official AIM client software includes advertisements and was available for Microsoft Windows, Windows Mobile, Classic Mac OS, macOS, Android, iOS, BlackBerry OS.
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Usage decline and product sunset Around 2011, AIM started to lose popularity rapidly, partly due to the quick rise of Gmail and its built-in real-time Google Chat instant messenger integration in 2011 and because many people migrated to SMS or iMessages text messaging and later, social networking websites and apps for instant messaging, in particular, Facebook Messenger, which was released as a standalone application the same year. AOL made a partnership to integrate AIM messaging in Google Talk, and had a feature for AIM users to send SMS messages directly from AIM to any number, as well as for SMS users to send an IM to any AIM user.
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As of June 2011, one source reported AOL Instant Messenger market share had collapsed to 0.73%. However, this number only reflected installed IM applications, and not active users. The engineers responsible for AIM claimed that they were unable to convince AOL management that free was the future.
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On March 3, 2012, AOL ended employment of AIM's development staff while leaving it active and with help support still provided. On October 6, 2017, it was announced that the AIM service would be discontinued on December 15; however, a non-profit development team known as Wildman Productions started up a server for older versions of AOL Instant Messenger, known as AIM Phoenix. The "AIM Man"
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The AIM mascot was designed by JoRoan Lazaro and was implemented in the first release in 1997. This was a yellow stickman-like figure, often called the "Running Man". The mascot appeared on all AIM logos and most wordmarks, and always appeared at the top of the buddy list. AIM's popularity in the late 1990s and the 2000s led to the "Running Man" becoming a familiar brand on the Internet. After over 14 years, the iconic logo disappeared as part of the AIM rebranding in 2011. However, in August 2013, the "Running Man" returned.
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In 2014, a Complex editor called it a "symbol of America". In April 2015, the Running Man was officially featured in the Virgin London Marathon, dressed by a person for the AOL-partnered Free The Children charity.
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Protocol The standard protocol that AIM clients used to communicate is called Open System for CommunicAtion in Realtime (OSCAR). Most AOL-produced versions of AIM and popular third party AIM clients use this protocol. However, AOL also created a simpler protocol called TOC that lacks many of OSCAR's features, but was sometimes used for clients that only require basic chat functionality. The TOC/TOC2 protocol specifications were made available by AOL, while OSCAR is a closed protocol that third parties had to reverse-engineer.
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In January 2008, AOL introduced experimental Extensible Messaging and Presence Protocol (XMPP) support for AIM, allowing AIM users to communicate using the standardized, open-source XMPP. However, in March 2008, this service was discontinued. In May 2011, AOL started offering limited XMPP support. On March 1, 2017, AOL announced (via XMPP-login-time messages) that the AOL XMPP gateway would be desupported, effective March 28, 2017.
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Privacy For privacy regulations, AIM had strict age restrictions. AIM accounts are available only for people over the age of 13; children younger than that were not permitted access to AIM. Under the AIM Privacy Policy, AOL had no rights to read or monitor any private communications between users. The profile of the user had no privacy. In November 2002, AOL targeted the corporate industry with Enterprise AIM Services (EAS), a higher security version of AIM.
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If public content was accessed, it could be used for online, print or broadcast advertising, etc. This was outlined in the policy and terms of service: "... you grant AOL, its parent, affiliates, subsidiaries, assigns, agents and licensees the irrevocable, perpetual, worldwide right to reproduce, display, perform, distribute, adapt and promote this Content in any medium". This allowed anything users posted to be used without a separate request for permission.
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AIM's security was called into question. AOL stated that it had taken great pains to ensure that personal information will not be accessed by unauthorized members, but that it cannot guarantee that it will not happen.
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AIM was different from other clients, such as Yahoo! Messenger, in that it did not require approval from users to be added to other users' buddy lists. As a result, it was possible for users to keep other unsuspecting users on their buddy list to see when they were online, read their status and away messages, and read their profiles. There was also a Web API to display one's status and away message as a widget on one's webpage. Though one could block a user from communicating with them and seeing their status, this did not prevent that user from creating a new account that would not automatically be blocked and therefore able to track their status. A more conservative privacy option was to select a menu feature that only allowed communication with users on one's buddy list; however, this option also created the side-effect of blocking all users who were not on one's buddy list.
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