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Ceres (; minor-planet designation: 1 Ceres) is a dwarf planet in the asteroid belt between the orbits of
Mars Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System, only being larger than Mercury. In the English language, Mars is named for the Roman god of war. Mars is a terrestrial planet with a thin at ...
and
Jupiter Jupiter is the fifth planet from the Sun and the largest in the Solar System. It is a gas giant with a mass more than two and a half times that of all the other planets in the Solar System combined, but slightly less than one-thousand ...
. It was the first
asteroid An asteroid is a minor planet of the inner Solar System. Sizes and shapes of asteroids vary significantly, ranging from 1-meter rocks to a dwarf planet almost 1000 km in diameter; they are rocky, metallic or icy bodies with no atmosphere. ...
discovered, on 1 January 1801, by Giuseppe Piazzi at Palermo Astronomical Observatory in Sicily and announced as a new
planet A planet is a large, rounded astronomical body that is neither a star nor its remnant. The best available theory of planet formation is the nebular hypothesis, which posits that an interstellar cloud collapses out of a nebula to create a you ...
. Ceres was later classified as an asteroid and then a dwarf planetthe only one always inside
Neptune Neptune is the eighth planet from the Sun and the farthest known planet in the Solar System. It is the fourth-largest planet in the Solar System by diameter, the third-most-massive planet, and the densest giant planet. It is 17 time ...
's orbit. Ceres's small size means that even at its brightest, it is too dim to be seen by the
naked eye Naked eye, also called bare eye or unaided eye, is the practice of engaging in visual perception unaided by a magnifying, light-collecting optical instrument, such as a telescope or microscope, or eye protection. Vision corrected to norma ...
, except under extremely dark skies. Its
apparent magnitude Apparent magnitude () is a measure of the brightness of a star or other astronomical object observed from Earth. An object's apparent magnitude depends on its intrinsic luminosity, its distance from Earth, and any extinction of the object's ...
ranges from 6.7 to 9.3, peaking at
opposition Opposition may refer to: Arts and media * ''Opposition'' (Altars EP), 2011 EP by Christian metalcore band Altars * The Opposition (band), a London post-punk band * '' The Opposition with Jordan Klepper'', a late-night television series on Com ...
(when it is closest to Earth) once every 15- to 16-month synodic period. As a result, its surface features are barely visible even with the most powerful telescopes, and little was known about it until the robotic
NASA The National Aeronautics and Space Administration (NASA ) is an independent agency of the US federal government responsible for the civil space program, aeronautics research, and space research. NASA was established in 1958, succeedin ...
spacecraft ''Dawn'' approached Ceres for its orbital mission in 2015. ''Dawn'' found Ceres's surface to be a mixture of water ice, and
hydrate In chemistry, a hydrate is a substance that contains water or its constituent elements. The chemical state of the water varies widely between different classes of hydrates, some of which were so labeled before their chemical structure was understo ...
d minerals such as carbonates and
clay Clay is a type of fine-grained natural soil material containing clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4). Clays develop plasticity when wet, due to a molecular film of water surrounding the clay pa ...
. Gravity data suggest Ceres to be partially differentiated into a muddy (ice-rock) mantle/core and a less dense but stronger crust that is at most 30% ice by volume. Although Ceres likely lacks an internal ocean of liquid water, brines still flow through the outer mantle and reach the surface, allowing cryovolcanoes such as
Ahuna Mons Ahuna Mons () is the largest mountain on the dwarf planet and asteroid Ceres. It protrudes above the cratered terrain, is not an impact feature, and is the only mountain of its kind on Ceres. Bright streaks run top to bottom on its slopes; these ...
to form roughly every fifty million years. This makes Ceres the closest known cryovolcanic body to the Sun, and the brines provide a potential habitat for microbial life. In January 2014, emissions of water vapour were detected around Ceres, creating a tenuous, transient
atmosphere An atmosphere () is a layer of gas or layers of gases that envelop a planet, and is held in place by the gravity of the planetary body. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. A ...
known as an exosphere. This was unexpected because vapour is usually a hallmark of
comet A comet is an icy, small Solar System body that, when passing close to the Sun, warms and begins to release gases, a process that is called outgassing. This produces a visible atmosphere or coma, and sometimes also a tail. These phenomena ...
s, not asteroids.


History


Discovery

In the years between the acceptance of
heliocentrism Heliocentrism (also known as the Heliocentric model) is the astronomical model in which the Earth and planets revolve around the Sun at the center of the universe. Historically, heliocentrism was opposed to geocentrism, which placed the Earth ...
in the 18th century and the discovery of
Neptune Neptune is the eighth planet from the Sun and the farthest known planet in the Solar System. It is the fourth-largest planet in the Solar System by diameter, the third-most-massive planet, and the densest giant planet. It is 17 time ...
in 1846, several astronomers argued that mathematical laws predicted the existence of a hidden or missing planet between the orbits of
Mars Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System, only being larger than Mercury. In the English language, Mars is named for the Roman god of war. Mars is a terrestrial planet with a thin at ...
and
Jupiter Jupiter is the fifth planet from the Sun and the largest in the Solar System. It is a gas giant with a mass more than two and a half times that of all the other planets in the Solar System combined, but slightly less than one-thousand ...
. In 1596 theoretical astronomer
Johannes Kepler Johannes Kepler (; ; 27 December 1571 – 15 November 1630) was a German astronomer, mathematician, astrologer, natural philosopher and writer on music. He is a key figure in the 17th-century Scientific Revolution, best known for his laws ...
believed that the ratios between planetary orbits would conform to " God's design" only with the addition of two planets: one between Jupiter and Mars and one between Venus and Mercury. Other theoreticians, such as
Immanuel Kant Immanuel Kant (, , ; 22 April 1724 – 12 February 1804) was a German philosopher and one of the central Enlightenment thinkers. Born in Königsberg, Kant's comprehensive and systematic works in epistemology, metaphysics, ethics, and ...
, pondered whether the gap had been created by the gravity of Jupiter; in 1761 astronomer and mathematician Johann Heinrich Lambert asked, "And who knows whether already planets are missing which have departed from the vast space between Mars and Jupiter? Does it then hold of celestial bodies as well as of the Earth, that the stronger chafe the weaker, and are Jupiter and Saturn destined to plunder forever?" In 1772 German astronomer
Johann Elert Bode Johann Elert Bode (; 19 January 1747 – 23 November 1826) was a German astronomer known for his reformulation and popularisation of the Titius–Bode law. Bode determined the orbit of Uranus and suggested the planet's name. Life and career ...
, citing Johann Daniel Titius, published a formula later known as the
Titius–Bode law The Titius–Bode law (sometimes termed just Bode's law) is a formulaic prediction of spacing between planets in any given solar system. The formula suggests that, extending outward, each planet should be approximately twice as far from the Sun as ...
that appeared to predict the orbits of the known planets but for an unexplained gap between Mars and Jupiter. This formula predicted that there ought to be another planet with an orbital radius near 2.8
astronomical unit The astronomical unit (symbol: au, or or AU) is a unit of length, roughly the distance from Earth to the Sun and approximately equal to or 8.3 light-minutes. The actual distance from Earth to the Sun varies by about 3% as Earth orbits ...
s (AU), or 420millionkm, from the Sun. The Titius–Bode law gained more credence with William Herschel's 1781 discovery of
Uranus Uranus is the seventh planet from the Sun. Its name is a reference to the Greek god of the sky, Uranus ( Caelus), who, according to Greek mythology, was the great-grandfather of Ares (Mars), grandfather of Zeus (Jupiter) and father of ...
near the predicted distance for a planet beyond
Saturn Saturn is the sixth planet from the Sun and the second-largest in the Solar System, after Jupiter. It is a gas giant with an average radius of about nine and a half times that of Earth. It has only one-eighth the average density of Earth; h ...
. In 1800 a group headed by Franz Xaver von Zach, editor of the German astronomical journal ("Monthly Correspondence"), sent requests to 24 experienced astronomers, whom he dubbed the " celestial police", asking that they combine their efforts and begin a methodical search for the expected planet. Although they did not discover Ceres, they later found the
asteroid An asteroid is a minor planet of the inner Solar System. Sizes and shapes of asteroids vary significantly, ranging from 1-meter rocks to a dwarf planet almost 1000 km in diameter; they are rocky, metallic or icy bodies with no atmosphere. ...
s Pallas, Juno, and Vesta. 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
tar Tar is a dark brown or black viscous liquid of hydrocarbons and free carbon, obtained from a wide variety of organic materials through destructive distillation. Tar can be produced from coal, wood, petroleum, or peat. "a dark brown or black bi ...
of the Catalogue of the Zodiacal stars of Mr la Caille", but found that "it was preceded by another". Instead of a star, Piazzi had found a moving star-like object, which he first thought was a comet. Piazzi observed Ceres 24 times, the final time on 11 February 1801, when illness interrupted his work. He announced his discovery on 24 January 1801 in letters to two fellow astronomers, his compatriot Barnaba Oriani of Milan and Bode in Berlin. He reported it as a comet, but "since its movement is so slow and rather uniform, it has occurred to me several times that it might be something better than a comet". In April, Piazzi sent his complete observations to Oriani, Bode, and French astronomer Jérôme Lalande. The information was published in the September 1801 issue of the . By this time, the apparent position of Ceres had changed (primarily due to Earth's motion around the Sun), and was too close to the Sun's glare for other astronomers to confirm Piazzi's observations. Towards the end of the year, Ceres should have been visible again, but after such a long time, it was difficult to predict its exact position. To recover Ceres, mathematician Carl Friedrich Gauss, then 24 years old, developed an efficient method of orbit determination. Within a few weeks, he predicted the path of Ceres and sent his results to von Zach. On 31 December 1801, von Zach and fellow celestial policeman Heinrich W. M. Olbers found Ceres near the predicted position and continued to record its position. At 2.8 AU from the Sun, Ceres appeared to fit the Titius–Bode law almost perfectly; when Neptune was discovered in 1846, eight AU closer than predicted, most astronomers concluded that the law was a coincidence. The early observers were able to calculate the size of Ceres only to within an
order of magnitude An order of magnitude is an approximation of the logarithm of a value relative to some contextually understood reference value, usually 10, interpreted as the base of the logarithm and the representative of values of magnitude one. Logarithmic di ...
. Herschel underestimated its diameter at in 1802; in 1811, German astronomer Johann Hieronymus Schröter overestimated it as . In the 1970s, infrared
photometry Photometry can refer to: * Photometry (optics), the science of measurement of visible light in terms of its perceived brightness to human vision * Photometry (astronomy), the measurement of the flux or intensity of an astronomical object's electro ...
enabled more accurate measurements of its
albedo Albedo (; ) is the measure of the diffuse reflection of solar radiation out of the total solar radiation and measured on a scale from 0, corresponding to a black body that absorbs all incident radiation, to 1, corresponding to a body that refle ...
, and Ceres's diameter was determined to within 10% of its true value of 939km.


Name and symbol

Piazzi's proposed name for his discovery was ''Ceres Ferdinandea'': ''Ceres'' after the Roman goddess of agriculture, whose earthly home, and oldest temple, lay in Sicily; and ''Ferdinandea'' in honour of Piazzi's monarch and patron, King FerdinandIII of
Sicily (man) it, Siciliana (woman) , population_note = , population_blank1_title = , population_blank1 = , demographics_type1 = Ethnicity , demographics1_footnotes = , demographi ...
. The latter was not acceptable to other nations and was dropped. Before von Zach's recovery of Ceres in December 1801, von Zach referred to the planet as ''
Hera In ancient Greek religion, Hera (; grc-gre, Ἥρα, Hḗrā; grc, Ἥρη, Hḗrē, label=none in Ionic and Homeric Greek) is the goddess of marriage, women and family, and the protector of women during childbirth. In Greek mythology, she ...
,'' and Bode referred to it as '' Juno''. Despite Piazzi's objections, those names gained currency in Germany before the object's existence was confirmed. Once it was, astronomers settled on Piazzi's name. The adjectival forms of ''Ceres'' are ''Cererian'' and ''Cererean'', both pronounced .
Cerium Cerium is a chemical element with the symbol Ce and atomic number 58. Cerium is a soft, ductile, and silvery-white metal that tarnishes when exposed to air. Cerium is the second element in the lanthanide series, and while it often shows the +3 ...
, a rare-earth element discovered in 1803, was named after the dwarf planet Ceres. The old astronomical symbol of Ceres, still used in astrology, is a sickle, . The sickle was one of the classical symbols of the goddess Ceres and was suggested, apparently independently, by von Zach and Bode in 1802. In form, it is similar to the symbol (a circle with a small cross beneath) of the planet Venus, but with a break in the circle. It had various minor graphic variants, including a reversed form typeset as a 'C' (the initial letter of the name ''Ceres'') with a plus sign. The generic asteroid symbol of a numbered disk, ①, was introduced in 1867 and quickly became the norm.


Classification

The categorisation of Ceres has changed more than once and has been the subject of some disagreement. Bode believed Ceres to be the "missing planet" he had proposed to exist between Mars and Jupiter. Ceres was assigned a planetary symbol and remained listed as a planet in astronomy books and tables (along with Pallas, Juno, and Vesta) for over half a century. As other objects were discovered in the neighbourhood of Ceres, astronomers began to suspect that it represented the first of a new class of objects. When Pallas was discovered in 1802, Herschel coined the term ''asteroid'' ("star-like") for these bodies, writing that "they resemble small stars so much as hardly to be distinguished from them, even by very good telescopes". In 1852 Johann Franz Encke, in the ''
Berliner Astronomisches Jahrbuch The ''Berliner Astronomisches Jahrbuch'' (abbrev. B.A.J.) is an astronomical ephemeris almanac and one of the longest publication series in astronomy. It was a compendium of ephemerides of all large Solar System bodies and of fundamental stars whi ...
'', declared the traditional system of granting planetary symbols too cumbersome for these new objects and introduced a new method of placing numbers before their names in order of discovery. Initially, the numbering system began with the fifth asteroid, 5 Astraea, as number1, but in 1867 Ceres was adopted into the new system under the name 1Ceres. By the 1860s, astronomers widely accepted that a fundamental difference existed between the major planets and asteroids such as Ceres, though the word "planet" had yet to be precisely defined. In the 1950s, scientists generally stopped considering most asteroids as planets, but Ceres sometimes retained its status after that because of its planet-like geophysical complexity. Then, in 2006, the debate surrounding
Pluto Pluto (minor-planet designation: 134340 Pluto) is a dwarf planet in the Kuiper belt, a ring of trans-Neptunian object, bodies beyond the orbit of Neptune. It is the ninth-largest and tenth-most-massive known object to directly orbit the S ...
led to calls for a definition of "planet", and the possible reclassification of Ceres, perhaps even its general reinstatement as a planet. A proposal before the
International Astronomical Union The International Astronomical Union (IAU; french: link=yes, Union astronomique internationale, UAI) is a nongovernmental organisation with the objective of advancing astronomy in all aspects, including promoting astronomical research, outreac ...
(IAU), the global body responsible for astronomical nomenclature and classification, defined a planet as "a celestial body that (a) has sufficient mass for its self-gravity to overcome rigid-body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (b) is in orbit around a star, and is neither a star nor a satellite of a planet". Had this resolution been adopted, it would have made Ceres the fifth planet in order from the Sun, but on 24 August 2006 the assembly adopted the additional requirement that a planet must have "
cleared the neighbourhood "Clearing the neighbourhood" (or dynamical dominance) around a celestial body's orbit describes the body becoming gravitationally dominant such that there are no other bodies of comparable size other than its natural satellites or those otherwise ...
around its orbit". Ceres is not a planet because it does not dominate its orbit, sharing it as it does with the thousands of other asteroids in the asteroid belt and constituting only about 40% of the belt's total mass. Bodies that met the first proposed definition but not the second, such as Ceres, were instead classified as dwarf planets. Planetary geologists still often ignore this definition and consider Ceres to be a planet anyway. Ceres is a dwarf planet, but there is some confusion about whether it is also an asteroid. A NASA webpage states that Vesta, the belt's second-largest object, is the largest asteroid. The IAU has been equivocal on the subject, though its
Minor Planet Center The Minor Planet Center (MPC) is the official body for observing and reporting on minor planets under the auspices of the International Astronomical Union (IAU). Founded in 1947, it operates at the Smithsonian Astrophysical Observatory. Function T ...
, the organisation charged with cataloguing such objects, notes that dwarf planets may have dual designations, and the joint IAU/
USGS The United States Geological Survey (USGS), formerly simply known as the Geological Survey, is a scientific agency of the United States government. The scientists of the USGS study the landscape of the United States, its natural resources, ...
/NASA ''Gazetteer'' categorizes Ceres as both asteroid and a dwarf planet.


Orbit

Ceres follows an orbit between Mars and Jupiter, near the middle of the asteroid belt, with an
orbital period The orbital period (also revolution period) is the amount of time a given astronomical object takes to complete one orbit around another object. In astronomy, it usually applies to planets or asteroids orbiting the Sun, moons orbiting pla ...
(year) of 4.6 Earth years. Compared to other planets and dwarf planets, Ceres's orbit is moderately tilted relative to that of Earth; its
inclination Orbital inclination measures the tilt of an object's orbit around a celestial body. It is expressed as the angle between a reference plane and the orbital plane or axis of direction of the orbiting object. For a satellite orbiting the Ea ...
(''i'') is 10.6°, compared to 7° for Mercury and 17° for Pluto. It is also slightly elongated, with an eccentricity (''e'') = 0.08, compared to 0.09 for Mars. Ceres is not part of an
asteroid family An asteroid family is a population of asteroids that share similar proper orbital elements, such as semimajor axis, eccentricity, and orbital inclination. The members of the families are thought to be fragments of past asteroid collisions. An ...
, probably due to its large proportion of ice, as smaller bodies with the same composition would have sublimated to nothing over the age of the Solar System. It was once thought to be a member of the Gefion family, the members of which share similar
proper orbital elements __NOTOC__ The proper orbital elements or proper elements of an orbit are constants of motion of an object in space that remain practically unchanged over an astronomically long timescale. The term is usually used to describe the three quantiti ...
, suggesting a common origin through an asteroid collision in the past. Ceres was later found to have a different composition from the Gefion family and appears to be an
interloper Interloper, Interlopers or The Interlopers may refer to: Entertainment * '' The Interloper: Lee Harvey Oswald Inside the Soviet Union'', a 2013 book by Peter Savodnik * Interloper (comics), a fictional character in the Marvel Comics universe * ...
, having similar orbital elements but not a common origin.


Resonances

Due to their small masses and large separations, objects within the asteroid belt rarely fall into gravitational resonances with each other. Nevertheless, Ceres is able to capture other asteroids into temporary 1:1 resonances (making them temporary
trojans Trojan or Trojans may refer to: * Of or from the ancient city of Troy * Trojan language, the language of the historical Trojans Arts and entertainment Music * ''Les Troyens'' ('The Trojans'), an opera by Berlioz, premiered part 1863, part 189 ...
), for periods from a few hundred thousand to more than two million years. Fifty such objects have been identified. Ceres is close to a 1:1 mean-motion orbital resonance with Pallas (their proper orbital periods differ by 0.2%), but not close enough to be significant over astronomical timescales.


Rotation and axial tilt

The rotation period of Ceres (the Cererian day) is 9hours and 4minutes; the small equatorial crater of Kait is selected as its
prime meridian A prime meridian is an arbitrary meridian (a line of longitude) in a geographic coordinate system at which longitude is defined to be 0°. Together, a prime meridian and its anti-meridian (the 180th meridian in a 360°-system) form a great ...
. Ceres has an axial tilt of 4°, small enough for its polar regions to contain permanently shadowed craters that are expected to act as cold traps and accumulate water ice over time, similar to what occurs on the Moon and Mercury. About 0.14% of water molecules released from the surface are expected to end up in the traps, hopping an average of three times before escaping or being trapped. ''
Dawn Dawn is the time that marks the beginning of twilight before sunrise. It is recognized by the appearance of indirect sunlight being scattered in Earth's atmosphere, when the centre of the Sun's disc has reached 18° below the observer's ...
'', the first spacecraft to orbit Ceres, determined that the north polar axis points at right ascension 19h 25m 40.3s (291.418°), declination +66° 45' 50" (about 1.5 degrees from
Delta Draconis Delta Draconis (δ Draconis, abbreviated Delta Dra, δ Dra), formally named Altais , is a yellow star in the constellation of Draco. It has an apparent visual magnitude of 3.0, making it easily visible to the naked eye. Based on paralla ...
), which means an axial tilt of 4°. This means that Ceres currently sees little to no seasonal variation in sunlight by latitude. Over the course of three million years, gravitational influence from Jupiter and Saturn has triggered cyclical shifts in Ceres's axial tilt, ranging from two to twenty degrees, meaning that seasonal variation in sun exposure has occurred in the past, with the last period of seasonal activity estimated at 14,000 years ago. Those craters that remain in shadow during periods of maximum axial tilt are the most likely to retain water ice from eruptions or cometary impacts over the age of the Solar System.


Geology

Ceres is the largest asteroid in the main asteroid belt. It has been classified as a Ctype or carbonaceous asteroid and, due to the presence of clay minerals, as a
G-type asteroid G-type asteroids are a relatively uncommon type of carbonaceous asteroid that makes up approximately 5% of asteroids. The most notable asteroid in this class is 1 Ceres. Characteristics Generally similar to the C-type objects, but contain a s ...
. It has a similar, but not identical, composition to that of carbonaceous chondrite meteorites. It is an oblate spheroid, with an equatorial diameter 8% larger than its polar diameter. Measurements from the ''Dawn'' spacecraft found a mean diameter of and a mass of . This gives Ceres a density of , suggesting that a quarter of its mass is water ice. Ceres comprises 40% of the estimated mass of the asteroid belt, and it has times the mass of the next asteroid, Vesta, but it is only 1.3% the mass of the
Moon The Moon is Earth's only natural satellite. It is the fifth largest satellite in the Solar System and the largest and most massive relative to its parent planet, with a diameter about one-quarter that of Earth (comparable to the width of ...
. It is close to being in
hydrostatic equilibrium In fluid mechanics, hydrostatic equilibrium (hydrostatic balance, hydrostasy) is the condition of a fluid or plastic solid at rest, which occurs when external forces, such as gravity, are balanced by a pressure-gradient force. In the planeta ...
, but some deviations from an equilibrium shape have yet to be explained. Assuming it is in equilibrium, Ceres is the only dwarf planet that is always within the orbit of Neptune. Modelling has suggested Ceres's rocky material is partially differentiated, and that it may possess a small core, but the data are also consistent with a
mantle A mantle is a piece of clothing, a type of cloak. Several other meanings are derived from that. Mantle may refer to: *Mantle (clothing), a cloak-like garment worn mainly by women as fashionable outerwear **Mantle (vesture), an Eastern Orthodox ve ...
of hydrated
silicate In chemistry, a silicate is any member of a family of polyatomic anions consisting of silicon and oxygen, usually with the general formula , where . The family includes orthosilicate (), metasilicate (), and pyrosilicate (, ). The name is a ...
s and no core. Because ''Dawn'' lacked a
magnetometer A magnetometer is a device that measures magnetic field or magnetic dipole moment. Different types of magnetometers measure the direction, strength, or relative change of a magnetic field at a particular location. A compass is one such device, ...
, it is not known if Ceres has a
magnetic field A magnetic field is a vector field that describes the magnetic influence on moving electric charges, electric currents, and magnetic materials. A moving charge in a magnetic field experiences a force perpendicular to its own velocity and to ...
; it is believed not to. Ceres's internal differentiation may be related to its lack of a natural satellite, as satellites of main belt asteroids are mostly believed to form from collisional disruption, creating an undifferentiated, rubble pile structure.


Surface


Composition

The surface composition of Ceres is homogeneous on a global scale, and is rich in
carbonate A carbonate is a salt of carbonic acid (H2CO3), characterized by the presence of the carbonate ion, a polyatomic ion with the formula . The word ''carbonate'' may also refer to a carbonate ester, an organic compound containing the carbonate ...
s and ammoniated phyllosilicates that have been altered by water, though water ice in the regolith varies from approximately 10% in polar latitudes to much drier, even ice-free, in the equatorial regions. Studies using the
Hubble Space Telescope The Hubble Space Telescope (often referred to as HST or Hubble) is a space telescope that was launched into low Earth orbit in 1990 and remains in operation. It was not the first space telescope, but it is one of the largest and most vers ...
show
graphite Graphite () is a crystalline form of the element carbon. It consists of stacked layers of graphene. Graphite occurs naturally and is the most stable form of carbon under standard conditions. Synthetic and natural graphite are consumed on la ...
,
sulfur Sulfur (or sulphur in British English) is a chemical element with the symbol S and atomic number 16. It is abundant, multivalent and nonmetallic. Under normal conditions, sulfur atoms form cyclic octatomic molecules with a chemical formul ...
, and
sulfur dioxide Sulfur dioxide (IUPAC-recommended spelling) or sulphur dioxide (traditional Commonwealth English) is the chemical compound with the formula . It is a toxic gas responsible for the odor of burnt matches. It is released naturally by volcanic a ...
on Ceres's surface. The graphite is evidently the result of space weathering on Ceres's older surfaces; the latter two are volatile under Cererian conditions and would be expected to either escape quickly or settle in cold traps, and so are evidently associated with areas with relatively recent geological activity.
Organic compound In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen or carbon-carbon bonds. Due to carbon's ability to catenate (form chains with other carbon atoms), millions of organic compounds are known. Th ...
s were detected in Ernutet Crater, and most of the planet's near surface is rich in carbon, at approximately 20% by mass. The carbon content is more than five times higher than in carbonaceous chondrite meteorites analysed on Earth. The surface carbon shows evidence of being mixed with products of rock-water interactions, such as clays. This chemistry suggests Ceres formed in a cold environment, perhaps outside the orbit of Jupiter, and that it accreted from ultra-carbon-rich materials in the presence of water, which could provide conditions favourable to organic chemistry. File:PIA21755-CeresMap-CraterNames-20170901.jpg, Black-and-white photographic map of Ceres, centred on 180° longitude, with official nomenclature (September 2017) File:PIA20126-Ceres-PolarRegions-Dawn-20151023.jpg, Ceres, polar regions (November 2015): North (left); south (right). The south pole is in shadow. "Ysolo Mons" has since been renamed "Yamor Mons."


Craters

''Dawn'' revealed that Ceres has a heavily cratered surface, though with fewer large craters than expected. Models based on the formation of the current asteroid belt had predicted Ceres should have ten to fifteen craters larger than in diameter. The largest confirmed crater on Ceres, Kerwan Basin, is across. The most likely reason for this is
viscous relaxation The viscosity of a fluid is a measure of its resistance to deformation at a given rate. For liquids, it corresponds to the informal concept of "thickness": for example, syrup has a higher viscosity than water. Viscosity quantifies the int ...
of the crust slowly flattening out larger impacts. Ceres's north polar region shows far more cratering than the equatorial region, with the eastern equatorial region in particular comparatively lightly cratered. The overall size frequency of craters of between twenty and a hundred kilometres (10–60mi) is consistent with their having originated in the Late Heavy Bombardment, with craters outside the ancient polar regions likely erased by early
cryovolcanism A cryovolcano (sometimes informally called an ice volcano) is a type of volcano that erupts volatiles such as water, ammonia or methane into an extremely cold environment that is at or below their freezing point. The process of formation is known ...
. Three large shallow basins (planitiae) with degraded rims are likely to be eroded craters. The largest,
Vendimia Planitia Ceres is a dwarf planet in the asteroid belt that lies between the orbits of Mars and Jupiter. The IAU has adopted two themes for naming surface features on Ceres: agricultural deities for craters and agricultural festivals for everything els ...
, at across, is also the largest single geographical feature on Ceres. Two of the three have higher than average ammonium concentrations. ''Dawn'' observed 4,423 boulders larger than in diameter on the surface of Ceres. These boulders likely formed through impacts, and are found within or near craters, though not all craters contain boulders. Large boulders are more numerous at higher latitudes. Boulders on Ceres are brittle and degrade rapidly due to thermal stress (at dawn and dusk, the surface temperature changes rapidly) and meteoritic impacts. Their maximum age is estimated to be 150million years, much shorter than the lifetime of boulders on Vesta.


Tectonic features

Although Ceres lacks
plate tectonics Plate tectonics (from the la, label= Late Latin, tectonicus, from the grc, τεκτονικός, lit=pertaining to building) is the generally accepted scientific theory that considers the Earth's lithosphere to comprise a number of larg ...
, with the vast majority of its surface features linked either to impacts or to cryovolcanic activity, several potentially
tectonic Tectonics (; ) are the processes that control the structure and properties of the Earth's crust and its evolution through time. These include the processes of mountain building, the growth and behavior of the strong, old cores of continents ...
features have been tentatively identified on its surface, particularly in its eastern hemisphere. The Samhain Catenae, kilometre-scale linear fractures on Ceres's surface, lack any apparent link to impacts and bear a stronger resemblance to pit crater chains, which are indicative of buried
normal fault In geology, a fault is a planar fracture or discontinuity in a volume of rock across which there has been significant displacement as a result of rock-mass movements. Large faults within Earth's crust result from the action of plate tectonic ...
s. Also, several craters on Ceres have shallow, fractured floors consistent with cryomagmatic intrusion.


Cryovolcanism

Ceres has one prominent mountain,
Ahuna Mons Ahuna Mons () is the largest mountain on the dwarf planet and asteroid Ceres. It protrudes above the cratered terrain, is not an impact feature, and is the only mountain of its kind on Ceres. Bright streaks run top to bottom on its slopes; these ...
; this appears to be a cryovolcano and has few craters, suggesting a maximum age of 240million years. Its relatively high gravitational field suggests it is dense, and thus composed more of rock than ice, and that its placement is likely due to
diapirism A diapir (; , ) is a type of igneous intrusion in which a more mobile and ductily deformable material is forced into brittle overlying rocks. Depending on the tectonic environment, diapirs can range from idealized mushroom-shaped Rayleigh–T ...
of a slurry of brine and silicate particles from the top of the mantle. It is roughly antipodal to Kerwan Basin. Seismic energy from the Kerwan-forming impact may have focused on the opposite side of Ceres, fracturing the outer layers of the crust and triggering the movement of high-viscosity cryomagma (muddy water ice softened by its content of salts) onto the surface. Kerwan too shows evidence of the effects of liquid water due to impact-melting of subsurface ice. A 2018
computer simulation Computer simulation is the process of mathematical modelling, performed on a computer, which is designed to predict the behaviour of, or the outcome of, a real-world or physical system. The reliability of some mathematical models can be deter ...
suggests that cryovolcanoes on Ceres, once formed, recede due to viscous relaxation over several hundred million years. The team identified 22 features as strong candidates for relaxed cryovolcanoes on Ceres's surface. Yamor Mons, an ancient, impact-cratered peak, resembles Ahuna Mons despite being much older, due to it lying in Ceres's northern polar region, where lower temperatures prevent viscous relaxation of the crust. Models suggest that, over the past billion years, one cryovolcano has formed on Ceres on average every fifty million years. The eruptions are not uniformly distributed over Ceres, but may be linked to ancient impact basins. The model suggests that, contrary to findings at Ahuna Mons, Cererian cryovolcanoes must be composed of far less dense material than average for Ceres's crust, or the observed viscous relaxation could not occur. An unexpectedly large number of Cererian craters have central pits, perhaps due to cryovolcanic processes; others have central peaks. Hundreds of bright spots ( faculae) have been observed by ''Dawn'', the brightest in the middle of Occator Crater. The bright spot in the centre of Occator is named Cerealia Facula, and the group of bright spots to its east,
Vinalia The Vinalia were Roman festivals of the wine harvest, wine vintage and gardens, held in honour of Jupiter and Venus. The ''Vinalia prima'' ("first Vinalia"), also known as the ''Vinalia urbana'' ("Urban Vinalia") was held on 23 April to bless an ...
Faculae. Occator possesses a pit 9–10 km wide, partially filled by a central dome. The dome post-dates the faculae and is likely due to freezing of a subterranean reservoir, comparable to pingos in Earth's Arctic region. A haze periodically appears above Cerealia, supporting the hypothesis that some sort of outgassing or sublimating ice formed the bright spots. In March 2016 ''Dawn'' found definitive evidence of water ice on the surface of Ceres at Oxo crater. On 9 December 2015 NASA scientists reported that the bright spots on Ceres may be due to a type of salt from evaporated brine containing magnesium sulfate hexahydrate (MgSO4·6H2O); the spots were also found to be associated with ammonia-rich clays.
Near-infrared Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from arou ...
spectra of these bright areas were reported in 2017 to be consistent with a large amount of sodium carbonate () and smaller amounts of ammonium chloride () or ammonium bicarbonate (). These materials have been suggested to originate from the crystallisation of brines that reached the surface. In August 2020 NASA confirmed that Ceres was a water-rich body with a deep reservoir of brine that percolated to the surface in hundreds of locations causing "bright spots", including those in Occator Crater.


Internal structure

The active geology of Ceres is driven by ice and brines. Water leached from rock is estimated to possess a
salinity Salinity () is the saltiness or amount of salt (chemistry), salt dissolved in a body of water, called saline water (see also soil salinity). It is usually measured in g/L or g/kg (grams of salt per liter/kilogram of water; the latter is dimensio ...
of around 5%. Altogether, Ceres is approximately 50% water by volume (compared to 0.1% for Earth) and 73% rock by mass. Ceres's largest craters are several kilometres deep, inconsistent with an ice-rich shallow subsurface. The fact that the surface has preserved craters almost in diameter indicates that the outermost layer of Ceres is roughly 1000 times stronger than water ice. This is consistent with a mixture of
silicate In chemistry, a silicate is any member of a family of polyatomic anions consisting of silicon and oxygen, usually with the general formula , where . The family includes orthosilicate (), metasilicate (), and pyrosilicate (, ). The name is a ...
s, hydrated salts and
methane clathrate Methane clathrate (CH4·5.75H2O) or (8CH4·46H2O), also called methane hydrate, hydromethane, methane ice, fire ice, natural gas hydrate, or gas hydrate, is a solid clathrate compound (more specifically, a clathrate hydrate) in which a large amou ...
s, with no more than 30% water ice by volume. Gravity measurements from ''Dawn'' have generated three competing models for Ceres's interior. In the three-layer model Ceres is thought to consist of an outer, thick crust of ice, salts and hydrated minerals and an inner muddy "
mantle A mantle is a piece of clothing, a type of cloak. Several other meanings are derived from that. Mantle may refer to: *Mantle (clothing), a cloak-like garment worn mainly by women as fashionable outerwear **Mantle (vesture), an Eastern Orthodox ve ...
" of hydrated rock, such as clays, separated by a layer of a muddy mixture of brine and rock. It is not possible to tell if Ceres's deep interior contains liquid or a core of dense material rich in metal, but the low central density suggests it may retain about 10%
porosity Porosity or void fraction is a measure of the void (i.e. "empty") spaces in a material, and is a fraction of the volume of voids over the total volume, between 0 and 1, or as a percentage between 0% and 100%. Strictly speaking, some tests measur ...
. One study estimated the densities of the core and mantle/crust to be 2.46–2.90 and 1.68–1.95g/cm3 respectively, with the mantle and crust together being thick. Only partial dehydration (expulsion of ice) from the core is expected, though the high density of the mantle relative to water ice reflects its enrichment in silicates and salts. That is, the core (if it exists), the mantle and crust all consist of rock and ice, though in different ratios. Ceres's mineral composition can be determined (indirectly) only for its outer . The solid outer crust, thick, is a mixture of ice, salts, and hydrated minerals. Under that is a layer that may contain a small amount of brine. This extends to a depth of at least the limit of detection. Under that is thought to be a mantle dominated by hydrated rocks such as clays. In one two-layer model Ceres consists of a core of
chondrule A chondrule (from Ancient Greek χόνδρος ''chondros'', grain) is a round grain found in a chondrite. Chondrules form as molten or partially molten droplets in space before being accreted to their parent asteroids. Because chondrites repr ...
s and a mantle of mixed ice and micron-sized solid particulates ("mud"). Sublimation of ice at the surface would leave a deposit of hydrated particulates perhaps twenty metres thick. The range of the extent of differentiation is consistent with the data, from a large, core of 75% chondrules and 25% particulates and a mantle of 75% ice and 25% particulates, to a small, core consisting nearly entirely of particulates and a mantle of 30% ice and 70% particulates. With a large core, the core–mantle boundary should be warm enough for pockets of brine. With a small core, the mantle should remain liquid below . In the latter case a 2% freezing of the liquid reservoir would compress the liquid enough to force some to the surface, producing cryovolcanism. A second two-layer model suggests a partial differentiation of Ceres into a volatile-rich crust and a denser mantle of hydrated silicates. A range of densities for the crust and mantle can be calculated from the types of meteorite thought to have impacted Ceres. With CI-class meteorites (density 2.46 g/cm3), the crust would be approximately thick and have a density of 1.68 g/cm3; with CM-class meteorites (density 2.9 g/cm3), the crust would be approximately thick and have a density of 1.9 g/cm3. Best-fit modelling yields a crust approximately thick with a density of approximately 1.25 g/cm3, and a mantle/core density of approximately 2.4 g/cm3.


Atmosphere

In 2017 ''Dawn'' confirmed that Ceres has a transient atmosphere of water vapour. Hints of an atmosphere had appeared in early 2014, when the Herschel Space Observatory detected localised mid-latitude sources of water vapour on Ceres, no more than in diameter, which each give off approximately molecules (3kg) of water per second. Two potential source regions, designated Piazzi (123°E, 21°N) and Region A (231°E, 23°N), were visualised in the near infrared as dark areas (Region A also has a bright centre) by the
Keck Observatory The W. M. Keck Observatory is an astronomical observatory with two telescopes at an elevation of 4,145 meters (13,600 ft) near the summit of Mauna Kea in the U.S. state of Hawaii. Both telescopes have aperture primary mirrors, and when ...
. Possible mechanisms for the vapour release are sublimation from approximately of exposed surface ice,
cryovolcanic A cryovolcano (sometimes informally called an ice volcano) is a type of volcano that erupts volatiles such as water, ammonia or methane into an extremely cold environment that is at or below their freezing point. The process of formation is k ...
eruptions resulting from radiogenic internal heat, or pressurisation of a subsurface ocean due to thickening of an overlying layer of ice. In 2015
David Jewitt David Clifford Jewitt (born 1958) is a British-American astronomer who studies the Solar System, especially its minor bodies. He is based at the University of California, Los Angeles, where he is a Member of the Institute for Geophysics and Pl ...
included Ceres in his list of
active asteroid Active asteroids are small Solar System bodies that have asteroid-like orbits but show comet-like visual characteristics. That is, they show comae, tails, or other visual evidence of mass-loss (like a comet), but their orbit remains within Jupi ...
s. Surface water ice is unstable at distances less than 5 AU from the Sun, so it is expected to sublime if exposed directly to solar radiation. Water ice can migrate from the deep layers of Ceres to the surface, but escapes in a short time. Surface sublimation would be expected to be lower when Ceres is farther from the Sun in its orbit, and internally powered emissions should not be affected by its orbital position. The limited data previously available suggested cometary-style sublimation, but evidence from ''Dawn'' suggests geologic activity could be at least partially responsible. Studies using ''Dawn's'' gamma ray and neutron detector (GRaND) reveal that Ceres accelerates electrons from the solar wind; the most accepted hypothesis is that these electrons are being accelerated by collisions between the solar wind and a tenuous water vapour exosphere. Bow shocks like these could also be explained by a transient magnetic field, but this is considered less likely, as the interior of Ceres is not thought to be sufficiently electrically conductive.


Origin and evolution

Ceres is a surviving protoplanet that formed 4.56billion years ago; alongside Pallas and Vesta, one of only three remaining in the inner Solar System, with the rest either merging to form terrestrial planets, being shattered in collisions or being ejected by Jupiter. Despite Ceres's current location, its composition is not consistent with having formed within the asteroid belt. It seems rather that it formed between the orbits of Jupiter and Saturn, and was deflected into the asteroid belt as Jupiter migrated outward. The discovery of ammonium salts in Occator Crater supports an origin in the outer Solar System, as ammonia is far more abundant in that region. The early geological evolution of Ceres was dependent on the heat sources available during and after its formation: impact energy from
planetesimal Planetesimals are solid objects thought to exist in protoplanetary disks and debris disks. Per the Chamberlin–Moulton planetesimal hypothesis, they are believed to form out of cosmic dust grains. Believed to have formed in the Solar System ...
accretion Accretion may refer to: Science * Accretion (astrophysics), the formation of planets and other bodies by collection of material through gravity * Accretion (meteorology), the process by which water vapor in clouds forms water droplets around nucl ...
and decay of
radionuclide A radionuclide (radioactive nuclide, radioisotope or radioactive isotope) is a nuclide that has excess nuclear energy, making it unstable. This excess energy can be used in one of three ways: emitted from the nucleus as gamma radiation; transfer ...
s (possibly including short-lived extinct radionuclides such as
aluminium-26 Aluminium-26 (26Al, Al-26) is a radioactive isotope of the chemical element aluminium, decaying by either positron emission or electron capture to stable magnesium-26. The half-life of 26Al is 7.17 (717,000) years. This is far too short for the ...
). These may have been sufficient to allow Ceres to differentiate into a rocky core and icy mantle, or even a liquid water ocean, soon after its formation. This ocean should have left an icy layer under the surface as it froze. The fact that ''Dawn'' found no evidence of such a layer suggests that Ceres's original crust was at least partially destroyed by later impacts thoroughly mixing the ice with the salts and silicate-rich material of the ancient seafloor and the material beneath. Ceres possesses surprisingly few large craters, suggesting that viscous relaxation and cryovolcanism have erased older geological features. The presence of clays and carbonates requires chemical reactions at temperatures above 50°C, consistent with hydrothermal activity. It has become considerably less geologically active over time, with a surface dominated by impact craters; nevertheless, evidence from ''Dawn'' reveals that internal processes have continued to sculpt Ceres's surface to a significant extent contrary to predictions that Ceres's small size would have ceased internal geological activity early in its history.


Habitability

Although Ceres is not as actively discussed as a potential home for
microbial A microorganism, or microbe,, ''mikros'', "small") and ''organism'' from the el, ὀργανισμός, ''organismós'', "organism"). It is usually written as a single word but is sometimes hyphenated (''micro-organism''), especially in olde ...
extraterrestrial life Extraterrestrial life, colloquially referred to as alien life, is life that may occur outside Earth and which did not originate on Earth. No extraterrestrial life has yet been conclusively detected, although efforts are underway. Such life might ...
as
Mars Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System, only being larger than Mercury. In the English language, Mars is named for the Roman god of war. Mars is a terrestrial planet with a thin at ...
,
Europa Europa may refer to: Places * Europe * Europa (Roman province), a province within the Diocese of Thrace * Europa (Seville Metro), Seville, Spain; a station on the Seville Metro * Europa City, Paris, France; a planned development * Europa Clif ...
, Enceladus, or
Titan Titan most often refers to: * Titan (moon), the largest moon of Saturn * Titans, a race of deities in Greek mythology Titan or Titans may also refer to: Arts and entertainment Fictional entities Fictional locations * Titan in fiction, fictiona ...
are, it has the most water of any body in the inner Solar System after Earth, and the likely brine pockets under its surface could provide habitats for life. It does not experience tidal heating, like Europa or Enceladus, but it is close enough to the Sun, and contains enough long-lived radioactive isotopes, to preserve liquid water in its subsurface for extended periods. The remote detection of
organic compound In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen or carbon-carbon bonds. Due to carbon's ability to catenate (form chains with other carbon atoms), millions of organic compounds are known. Th ...
s and the presence of water mixed with 20%
carbon Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent—its atom making four electrons available to form covalent chemical bonds. It belongs to group 14 of the periodic table. Carbon ma ...
by mass in its near surface could provide conditions favourable to organic chemistry. Of the biochemical elements, Ceres is rich in carbon,
hydrogen Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-to ...
,
oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements ...
and
nitrogen Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at se ...
, but
phosphorus Phosphorus is a chemical element with the symbol P and atomic number 15. Elemental phosphorus exists in two major forms, white phosphorus and red phosphorus, but because it is highly reactive, phosphorus is never found as a free element on Ea ...
has yet to be detected, and sulfur, despite being suggested by Hubble UV observations, was not detected by ''Dawn''.


Observation and exploration


Observation

When in opposition near its perihelion, Ceres can reach an
apparent magnitude Apparent magnitude () is a measure of the brightness of a star or other astronomical object observed from Earth. An object's apparent magnitude depends on its intrinsic luminosity, its distance from Earth, and any extinction of the object's ...
of +6.7. This is too dim to be visible to the average
naked eye Naked eye, also called bare eye or unaided eye, is the practice of engaging in visual perception unaided by a magnifying, light-collecting optical instrument, such as a telescope or microscope, or eye protection. Vision corrected to norma ...
, but under ideal viewing conditions, keen eyes may be able to see it. Vesta is the only other asteroid that can regularly reach a similarly bright magnitude, while Pallas and
7 Iris Iris ( minor planet designation: 7 Iris) is a large main-belt asteroid and possible remnant planetesimal orbiting the Sun between Mars and Jupiter. It is the fourth-brightest object in the asteroid belt. 7 Iris is classified as an S-type aste ...
do so only when both in opposition and near perihelion. When in conjunction, Ceres has a magnitude of around +9.3, which corresponds to the faintest objects visible with 10×50 binoculars; thus it can be seen with such binoculars in a naturally dark and clear night sky around
new moon In astronomy, the new moon is the first lunar phase, when the Moon and Sun have the same ecliptic longitude. At this phase, the lunar disk is not visible to the naked eye, except when it is silhouetted against the Sun during a solar ecl ...
. On 13 November 1984 an
occultation An occultation is an event that occurs when one object is hidden from the observer by another object that passes between them. The term is often used in astronomy, but can also refer to any situation in which an object in the foreground blocks ...
of the star BD+8°471 by Ceres was observed in Mexico, Florida and across the
Caribbean The Caribbean (, ) ( es, El Caribe; french: la Caraïbe; ht, Karayib; nl, De Caraïben) is a region of the Americas that consists of the Caribbean Sea, its islands (some surrounded by the Caribbean Sea and some bordering both the Caribbean ...
, allowing better measurements of its size, shape and albedo. On 25 June 1995 Hubble obtained ultraviolet images of Ceres with resolution. In 2002 the
Keck Observatory The W. M. Keck Observatory is an astronomical observatory with two telescopes at an elevation of 4,145 meters (13,600 ft) near the summit of Mauna Kea in the U.S. state of Hawaii. Both telescopes have aperture primary mirrors, and when ...
obtained infrared images with resolution using adaptive optics. Before the ''Dawn'' mission only a few surface features had been unambiguously detected on Ceres. High-resolution
ultraviolet Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nm (with a corresponding frequency around 30  PHz) to 400 nm (750  THz), shorter than that of visible light, but longer than X-rays. UV radiation ...
Hubble images in 1995 showed a dark spot on its surface, which was nicknamed "Piazzi" in honour of the discoverer of Ceres. It was thought to be a crater. Visible-light images of a full rotation taken by Hubble in 2003 and 2004 showed eleven recognisable surface features, the natures of which were undetermined. One of them corresponded to the Piazzi feature.
Near-infrared Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from arou ...
images over a whole rotation, taken with adaptive optics by the Keck Observatory in 2012, showed bright and dark features moving with Ceres's rotation. Two dark features were circular and were presumed to be craters; one was observed to have a bright central region, and the other was identified as the Piazzi feature. ''Dawn'' eventually revealed Piazzi to be a dark region in the middle of
Vendimia Planitia Ceres is a dwarf planet in the asteroid belt that lies between the orbits of Mars and Jupiter. The IAU has adopted two themes for naming surface features on Ceres: agricultural deities for craters and agricultural festivals for everything els ...
, close to the crater
Dantu Dantu District () is one of three districts of Zhenjiang, Jiangsu province, China. A development called Dantu New City was constructed in the district and was underoccupied since around 2005 and criticized as a ghost city by international media. Ho ...
, and the other dark feature to be within Hanami Planitia and close to Occator Crater.


''Dawn'' mission

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 proposed a high-priority mission to explore the asteroid belt using a spacecraft with an ion engine. Funding remained problematic for nearly a decade, but by 2004 the ''Dawn'' vehicle passed its critical design review. ''Dawn'', the first space mission to visit either Vesta or Ceres, was launched on 27 September 2007. On 3 May 2011 ''Dawn'' acquired its first targeting image from Vesta. After orbiting Vesta for thirteen months, ''Dawn'' used its ion engine to depart for Ceres, with gravitational capture occurring on 6 March 2015 at a separation of , four months before the ''
New Horizons ''New Horizons'' is an interplanetary space probe that was launched as a part of NASA's New Frontiers program. Engineered by the Johns Hopkins University Applied Physics Laboratory (APL) and the Southwest Research Institute (SwRI), with a ...
'' flyby of Pluto. The spacecraft instrumentation included a framing camera, a
visual The visual system comprises the sensory organ (the eye) and parts of the central nervous system (the retina containing photoreceptor cells, the optic nerve, the optic tract and the visual cortex) which gives organisms the sense of sight ...
and
infrared Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of Light, visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from ...
spectrometer, and a gamma-ray and
neutron The neutron is a subatomic particle, symbol or , which has a neutral (not positive or negative) charge, and a mass slightly greater than that of a proton. Protons and neutrons constitute the atomic nucleus, nuclei of atoms. Since protons and ...
detector. These instruments examined Ceres's shape and elemental composition. On 13 January 2015, as ''Dawn'' approached Ceres, the spacecraft took its first images at near-Hubble resolution, revealing impact craters and a small high-albedo spot on the surface. Additional imaging sessions, at increasingly better resolution took place from February to April. ''Dawn's'' mission profile called for it to study Ceres from a series of circular polar orbits at successively lower altitudes. It entered its first observational orbit ("RC3") around Ceres at an altitude of on 23 April 2015, staying for only one orbit (15 days). The spacecraft then reduced its orbital distance to for its second observational orbit ("survey") for three weeks, then down to ("HAMO;" high altitude mapping orbit) for two months and then down to its final orbit at ("LAMO;" low altitude mapping orbit) for at least three months. In October 2015 NASA released a true-colour portrait of Ceres made by ''Dawn''. In 2017 ''Dawns mission was extended to perform a series of closer orbits around Ceres until the
hydrazine Hydrazine is an inorganic compound with the chemical formula . It is a simple pnictogen hydride, and is a colourless flammable liquid with an ammonia-like odour. Hydrazine is highly toxic unless handled in solution as, for example, hydrazine ...
used to maintain its orbit ran out. ''Dawn'' soon discovered evidence of cryovolcanism. Two distinct bright spots (or high-albedo features) inside a crater (different from the bright spots observed in earlier Hubble images) were seen in a 19 February 2015 image, leading to speculation about a possible cryovolcanic origin or outgassing. On 2 September 2016 scientists from the ''Dawn'' team argued in a ''
Science Science is a systematic endeavor that builds and organizes knowledge in the form of testable explanations and predictions about the universe. Science may be as old as the human species, and some of the earliest archeological evidence ...
'' paper that Ahuna Mons was the strongest evidence yet for cryovolcanic features on Ceres. On 11 May 2015 NASA released a higher-resolution image showing that the spots were composed of multiple smaller spots. 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 hexahydrate (MgSO4·6H2O); the spots were also found to be associated with
ammonia Ammonia is an inorganic compound of nitrogen and hydrogen with the formula . A stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a distinct pungent smell. Biologically, it is a common nitrogenous ...
-rich clays. In June 2016 near-infrared spectra of these bright areas were found to be consistent with a large amount of sodium carbonate (), implying that recent geologic activity was probably involved in the creation of the bright spots. From June to October 2018 ''Dawn'' orbited Ceres from as close as to as far away as . The ''Dawn'' mission ended on 1 November 2018 after the spacecraft ran out of fuel.


Future missions

In 2020, an ESA team proposed the Calathus Mission concept, a followup mission to Occator Crater, to return a sample of the bright carbonate faculae and dark organics to Earth. The Chinese Space Agency is designing a sample-return mission from Ceres that would take place during the 2020s.


See also

*
List of exceptional asteroids The following is a collection of lists of asteroids of the Solar System that are exceptional in some way, such as their size or orbit. For the purposes of this article, "asteroid" refers to minor planets out to the orbit of Neptune, and includes ...
* List of Solar System objects by size


Notes


References


External links


Ceres Trek – An integrated map browser of datasets and maps for 1CeresCeres 3D Model – NASADestination Ceres:Breakfast at Dawn – NASA''Dawn'' mission home page
at JPL
Google Ceres 3D
interactive map of the dwarf planet

from keplersdiscovery.com
Animated reprojected colourised map of Ceres
(22 February 2015) *
Rotating relief model
of Ceres by Seán Doran (about 60% of a full rotation; starts with Occator midway above centre) * * {{Authority control 000001 000001 Discoveries by Giuseppe Piazzi Named minor planets Minor planets visited by spacecraft Articles containing video clips 000001 000001 000001 18010101 Dwarf planets