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= = History = = |
= = = Discovery = = = |
Johann Elert Bode , in 1772 , first suggested that an undiscovered planet could exist between the orbits of Mars and Jupiter . Kepler had already noticed the gap between Mars and Jupiter in 1596 . Bode based his idea on the Titius – Bode law — a now @-@ discredited hypothesis Johann Daniel Titius first proposed in 176... |
One of the astronomers selected for the search was Giuseppe Piazzi , a Catholic priest at the Academy of Palermo , Sicily . Before receiving his invitation to join the group , Piazzi discovered Ceres on 1 January 1801 . He was searching for " the 87th [ star ] of the Catalogue of the Zodiacal stars of Mr la Caille " ,... |
By this time , the apparent position of Ceres had changed ( mostly due to Earth 's orbital motion ) , and was too close to the Sun 's glare for other astronomers to confirm Piazzi 's observations . Toward the end of the year , Ceres should have been visible again , but after such a long time it was difficult to predic... |
The early observers were only able to calculate the size of Ceres to within an order of magnitude . Herschel underestimated its diameter as 260 km in 1802 , whereas in 1811 Johann Hieronymus Schröter overestimated it as 2 @,@ 613 km . |
= = = Name = = = |
Piazzi originally suggested the name Cerere Ferdinandea for his discovery , after the goddess Ceres ( Roman goddess of agriculture , Cerere in Italian , who was believed to have originated in Sicily and whose oldest temple was there ) and King Ferdinand of Sicily . " Ferdinandea " , however , was not acceptable to oth... |
The regular adjectival forms of the name are Cererian and Cererean , derived from the Latin genitive Cereris , but Ceresian is occasionally seen for the goddess ( as in the sickle @-@ shaped Ceresian Lake ) , as is the shorter form Cerean . |
The old astronomical symbol of Ceres is a sickle , 〈 ⚳ 〉 ( ) , similar to Venus ' symbol 〈 ♀ 〉 but with a break in the circle . It has a variant 〈 〉 , reversed under the influence of the initial letter ' C ' of ' Ceres ' . These were later replaced with the generic asteroid symbol of a numbered disk , 〈 ① 〉 . |
Cerium , a rare @-@ earth element discovered in 1803 , was named after Ceres . In the same year another element was also initially named after Ceres , but when cerium was named , its discoverer changed the name to palladium , after the second asteroid , 2 Pallas . |
= = = Classification = = = |
The categorization of Ceres has changed more than once and has been the subject of some disagreement . Johann Elert Bode believed Ceres to be the " missing planet " he had proposed to exist between Mars and Jupiter , at a distance of 419 million km ( 2 @.@ 8 AU ) from the Sun . Ceres was assigned a planetary symbol , ... |
As other objects were discovered in the neighborhood of Ceres , it was realized that Ceres represented the first of a new class of objects . In 1802 , with the discovery of 2 Pallas , William Herschel coined the term asteroid ( " star @-@ like " ) for these bodies , writing that " they resemble small stars so much as ... |
The 2006 debate surrounding Pluto and what constitutes a planet led to Ceres being considered for reclassification as a planet . A proposal before the International Astronomical Union for the definition of a planet would have defined a planet as " a celestial body that ( a ) has sufficient mass for its self @-@ gravit... |
Ceres is the largest object in the asteroid belt . It is sometimes assumed that Ceres has been reclassified as a dwarf planet , and that it is therefore no longer considered an asteroid . For example , a news update at Space.com spoke of " Pallas , the largest asteroid , and Ceres , the dwarf planet formerly classifie... |
= = Orbit = = |
Ceres follows an orbit between Mars and Jupiter , within the asteroid belt , with a period of 4 @.@ 6 Earth years . The orbit is moderately inclined ( i |
= 10 @.@ 6 ° compared to 7 ° for Mercury and 17 ° for Pluto ) and moderately eccentric ( e = |
0 @.@ 08 compared to 0 @.@ 09 for Mars ) . |
The diagram illustrates the orbits of Ceres ( blue ) and several planets ( white and gray ) . The segments of orbits below the ecliptic are plotted in darker colors , and the orange plus sign is the Sun 's location . The top left diagram is a polar view that shows the location of Ceres in the gap between Mars and Jupi... |
Ceres was once thought to be a member of an asteroid family . The asteroids of this family share similar proper orbital elements , which may indicate a common origin through an asteroid collision some time in the past . Ceres was later found to have spectral properties different from other members of the family , whic... |
= = = Resonances = = = |
Ceres is in a near @-@ 1 : 1 mean @-@ motion orbital resonance with Pallas ( their proper orbital periods differ by 0 @.@ 2 % ) . However , a true resonance between the two would be unlikely ; due to their small masses relative to their large separations , such relationships among asteroids are very rare . Nevertheles... |
= = = Transits of planets from Ceres = = = |
Mercury , Venus , Earth , and Mars can all appear to cross the Sun , or transit it , from a vantage point on Ceres . The most common transits are those of Mercury , which usually happen every few years , most recently in 2006 and 2010 . The most recent transit of Venus was in 1953 , and the next will be in 2051 ; the ... |
= = Rotation and axial tilt = = |
The rotation period of Ceres ( the Cererian day ) is 9 hours and 4 minutes . It has a small axial tilt of 4 ° . This is nevertheless large enough for Ceres 's polar regions to contain permanently shadowed craters that are expected to act as cold traps and accumulate water ice over time , similar to the situation on th... |
= = Geology = = |
Ceres has a mass of 9 @.@ 39 × 1020 kg as determined from the Dawn spacecraft . With this mass Ceres comprises approximately a third of the estimated total 3 @.@ 0 ± 0 @.@ 2 × 1021 kg mass of the asteroid belt , which is in turn approximately 4 % of the mass of the Moon . Ceres is massive enough to give it a nearly sp... |
= = = Surface = = = |
The surface composition of Ceres is broadly similar to that of C @-@ type asteroids . Some differences do exist . The ubiquitous features in Ceres ' IR spectrum are those of hydrated materials , which indicate the presence of significant amounts of water in its interior . Other possible surface constituents include ir... |
Ceres ' surface is relatively warm . The maximum temperature with the Sun overhead was estimated from measurements to be 235 K ( approximately − 38 ° C , − 36 ° F ) on 5 May 1991 . Ice is unstable at this temperature . Material left behind by the sublimation of surface ice could explain the dark surface of Ceres compa... |
= = = = Observations prior to Dawn = = = = |
Prior to the Dawn mission , only a few surface features had been unambiguously detected on Ceres . High @-@ resolution ultraviolet Hubble Space Telescope images taken in 1995 showed a dark spot on its surface , which was nicknamed " Piazzi " in honor of the discoverer of Ceres . This was thought to be a crater . Later... |
These last observations indicated that the north pole of Ceres pointed in the direction of right ascension 19 h 24 min ( 291 ° ) , declination + 59 ° , in the constellation Draco , resulting in an axial tilt of approximately 3 ° . Dawn later determined that the north polar axis actually points at right ascension 19 h ... |
= = = = Observations by Dawn = = = = |
Dawn revealed a large number of craters with low relief , indicating that they lie over a relatively soft surface , probably of water ice . One crater , with extremely low relief , is 270 km ( 170 mi ) in diameter , reminiscent of large , flat craters on Tethys and Iapetus . An unexpectedly large number of Cererian cr... |
On 9 December 2015 , NASA scientists reported that the bright spots on Ceres may be related to a type of salt , particularly a form of brine containing magnesium sulfate hexahydrite ( MgSO4 · 6H2O ) ; the spots were also found to be associated with ammonia @-@ rich clays . Another team thinks the salts are sodium carb... |
= = = Internal structure = = = |
Ceres ' oblateness is consistent with a differentiated body , a rocky core overlain with an icy mantle . This 100 @-@ kilometer @-@ thick mantle ( 23 % – 28 % of Ceres by mass ; 50 % by volume ) contains up to 200 million cubic kilometers of water , which would be more than the amount of fresh water on Earth . This re... |
= = Atmosphere = = |
There are indications that Ceres may have a tenuous water vapor atmosphere outgassing from water ice on the surface . |
Surface water ice is unstable at distances less than 5 AU from the Sun , so it is expected to sublime if it is exposed directly to solar radiation . Water ice can migrate from the deep layers of Ceres to the surface , but escapes in a very short time . As a result , it is difficult to detect water vaporization . Water... |
In early 2014 , using data from the Herschel Space Observatory , it was discovered that there are several localized ( not more than 60 km in diameter ) mid @-@ latitude sources of water vapor on Ceres , which each give off approximately 1026 molecules ( or 3 kg ) of water per second . Two potential source regions , de... |
= = Origin and evolution = = |
Ceres is possibly a surviving protoplanet ( planetary embryo ) , which formed 4 @.@ 57 billion years ago in the asteroid belt . Although the majority of inner Solar System protoplanets ( including all lunar- to Mars @-@ sized bodies ) either merged with other protoplanets to form terrestrial planets or were ejected fr... |
The geological evolution of Ceres was dependent on the heat sources available during and after its formation : friction from planetesimal accretion , and decay of various radionuclides ( possibly including short @-@ lived isotopes such as the cosmogenic nuclide aluminium @-@ 26 ) . These are thought to have been suffi... |
Today , Ceres appears to be a geologically inactive body , with a surface sculpted only by impacts . The presence of significant amounts of water ice in its composition raises the possibility that Ceres has or had a layer of liquid water in its interior . This hypothetical layer is often called an ocean . If such a la... |
= = Potential habitability = = |
Although not as actively discussed as a potential home for microbial extraterrestrial life as Mars , Titan , Europa or Enceladus , there is evidence that Ceres ' icy mantle was once a watery subterranean ocean , and that has led to speculations that life could have existed there , and that hypothesized ejecta bearing ... |
= = Observation and exploration = = |
= = = Observation = = = |
When Ceres has an opposition near the perihelion , it can reach a visual magnitude of + 6 @.@ 7 . This is generally regarded as too dim to be seen with the naked eye , but under exceptional viewing conditions a very sharp @-@ sighted person may be able to see it . Ceres was at its brightest ( 6 @.@ 73 ) on 18 December... |
Some notable observations and milestones for Ceres include : |
1984 November 13 : An occultation of a star by Ceres observed in Mexico , Florida and across the Caribbean . |
1995 June 25 : Ultraviolet Hubble Space Telescope images with 50 @-@ kilometer resolution . |
2002 : Infrared images with 30 km resolution taken with the Keck telescope using adaptive optics . |
2003 and 2004 : Visible light images with 30 km resolution ( the best prior to the Dawn mission ) taken using Hubble . |
2012 December 22 : Ceres occulted the star TYC 1865 @-@ 00446 @-@ 1 over parts of Japan , Russia , and China . Ceres ' brightness was magnitude 6 @.@ 9 and the star , 12 @.@ 2 . |
2014 : Ceres was found to have an atmosphere with water vapor , confirmed by the Herschel space telescope . |
2015 : The NASA Dawn spacecraft approached and orbited Ceres , sending detailed images and scientific data back to Earth . |
= = = Exploration = = = |
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