Discovery[1] | |||||||||
---|---|---|---|---|---|---|---|---|---|
Discovered by | Giuseppe Piazzi | ||||||||
Discovery date | 1 January 1801 | ||||||||
Designations | |||||||||
(1) Ceres | |||||||||
Pronunciation | /ˈsɪəriːz/ | ||||||||
Named after | Cerēs | ||||||||
| |||||||||
Adjectives | Cererean, -ian /sɪˈrɪəriən/ | ||||||||
Symbol | |||||||||
Orbital characteristics[2] | |||||||||
Epoch 27 April 2019 (JD 2458600.5) | |||||||||
Aphelion | 2.9796467093 AU (445,749,000 km) | ||||||||
Perihelion | 2.5586835997 AU (382,774,000 km) | ||||||||
2.7691651545 AU (414,261,000 km) | |||||||||
Eccentricity | 0.07600902910 | ||||||||
4.61 yr 1683.14570801 d | |||||||||
466.6 d 1.278 yr | |||||||||
Average orbital speed | 17.905 km/s | ||||||||
4.9251163° | |||||||||
Inclination | 10.59406704° to ecliptic 9.20° to invariable plane[3] | ||||||||
80.3055316° | |||||||||
73.5976941° | |||||||||
Proper orbital elements[4] | |||||||||
Proper semi-major axis | 2.7670962 AU | ||||||||
Proper eccentricity | 0.1161977 | ||||||||
Proper inclination | 9.6474122° | ||||||||
Proper mean motion | 78.193318 deg / yr | ||||||||
Proper orbital period | 4.60397 yr (1681.601 d) | ||||||||
Precession of perihelion | 54.070272 arcsec / yr | ||||||||
Precession of the ascending node | −59.170034 arcsec / yr | ||||||||
Physical characteristics | |||||||||
Dimensions | (964.4 × 964.2 × 891.8) ± 0.2 km[2] | ||||||||
Mean diameter | 939.4±0.2 km[2] | ||||||||
Mean radius | 469.73 km[5] | ||||||||
2,770,000 km2[6] | |||||||||
Volume | 434,000,000 km3[6] | ||||||||
Mass | (9.3835±0.0001)×1020 kg[2] 0.00016 Earths 0.0128 Moons | ||||||||
Mean density | 2.162±0.008 g/cm3[2] | ||||||||
Equatorial surface gravity | 0.28 m/s2[6] 0.029 g | ||||||||
0.36±0.15[7][a] (estimate) | |||||||||
Equatorial escape velocity | 0.51 km/s[6] | ||||||||
9.074170±0.000001 h[2] | |||||||||
Equatorial rotation velocity | 92.61 m/s[6] | ||||||||
≈4°[9] | |||||||||
North pole right ascension | 291.42744°[10] | ||||||||
North pole declination | 66.76033°[5] | ||||||||
0.090±0.0033 (V-band)[11] | |||||||||
| |||||||||
C[14] | |||||||||
3.34[2] | |||||||||
0.854″ to 0.339″ | |||||||||
Ceres (/ˈsɪəriːz/;[17] minor-planet designation: 1 Ceres) is the largest astronomical object in the asteroid belt between the orbits of Mars and Jupiter. The first asteroid discovered, Ceres was first observed on 1 January 1801 by Giuseppe Piazzi at Palermo Astronomical Observatory. Originally considered a planet, it was reclassified as an asteroid in the 1850s after the discovery of over 20 other objects in similar orbits. In 2006, it was reclassified again as a dwarf planet because, at 940 km (580 mi) in diameter, it is the only asteroid large enough to be rounded by its own gravity. This makes Ceres both the smallest recognized dwarf planet and the only one inside Neptune's orbit.
Ceres's small size means that even at its brightest, it is too dim to be seen by the naked eye, except under extremely dark skies. Its apparent magnitude ranges from 6.7 to 9.3, peaking at opposition once during its 15- to 16-month synodic period. Its surface features are barely visible even with the most powerful telescopes, and little was known of them until the robotic NASA spacecraft Dawn entered orbit around Ceres on 6 March 2015.
Dawn found Ceres's surface to be a mixture of water ice and hydrated minerals such as carbonates and clay. 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. Despite this, Ceres's small size means that any internal ocean of liquid water it may have possessed has likely frozen by now, though brines still flow through the outer mantle and reach the surface, allowing cryovolcanoes such as Ahuna Mons to form at the rate of about one every 50 million years. These brines provide a potential habitat for microbial life. In January 2014, emissions of water vapor were detected around Ceres, creating a tenuous, transient atmosphere known as an exosphere. This was unexpected because large bodies in the asteroid belt typically do not emit vapor, a hallmark of comets. This makes Ceres the closest cryovolcanic body to the Sun known to date.
History
Discovery
For many years after the acceptance of heliocentrism, several astronomers argued that mathematical laws predicted the existence of a hidden or missing planet between the orbits of Mars and Jupiter. In 1596, theoretical astronomer and mystic[18] Johannes Kepler believed that the ratios between planetary orbits only conformed to God's design with the addition of two planets: one between Jupiter and Mars and one between Venus and Mercury.[19] Many theoreticians, such as Immanuel Kant, pondered whether the gap had been cleared 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?" [19]
In 1772, German astronomer Johann Elert Bode, citing Johann Daniel Titius, published a numerical procession known as the Titius–Bode law (now discredited), which noted that each planet was twice as far from the Sun as the preceding, but for an unexplained gap between Mars and Jupiter.[19][20] The pattern predicted that there ought to be another planet with an orbital radius near 2.8 astronomical units (AU) from the Sun.[20] The Titius-Bode law got a boost with William Herschel's discovery of Uranus near the predicted distance for a planet beyond Saturn.[19] In 1800, a group headed by Franz Xaver von Zach, editor of the astronomical journal Monatliche Correspondenz (Monthly Correspondence), sent requests to 24 experienced astronomers (whom he dubbed the "celestial police"),[20] asking that they combine their efforts and begin a methodical search for the expected planet.[20] Although they did not discover Ceres, they later found the asteroids 2 Pallas, 3 Juno and 4 Vesta.[20]
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.[21] He was searching for "the 87th [star] of the Catalogue of the Zodiacal stars of Mr la Caille",[19] but found that "it was preceded by another".[19] Instead of a star, Piazzi had found a moving star-like object, which he first thought was a comet.[22] Piazzi observed Ceres a total of 24 times, the final time on 11 February 1801, when illness interrupted his observations. He announced his discovery on 24 January 1801 in letters to only two fellow astronomers, his compatriot Barnaba Oriani of Milan and Bode in Berlin.[23] 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".[19] 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 Monatliche Correspondenz.[22]
By this time, the apparent position of Ceres had changed (mostly 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. Toward 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.[22] In 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 thus recovered it.[22]
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 (160 mi) in 1802, whereas in 1811 German astronomer Johann Hieronymus Schröter overestimated it as 2,613 km (1,624 mi).[24] It was not until the 1970s, when infrared photometry enabled more accurate measurements of its albedo, that Ceres's diameter was determined to within 10% of its actual value.[24]
Name and symbol
Piazzi's name for his discovery was Ceres Ferdinandea: 'Ceres' after the Roman goddess of agriculture, whose earthly home, and oldest temple, lay in Sicily; 'Ferdinandea' in honor of Piazzi's monarch and patron, King Ferdinand of Sicily.[22] The latter was not acceptable to other nations and was dropped. Before Von Zach's confirmation in December 1801, he referred to the planet as Hera, though Bode preferred Juno. Despite Piazzi's objections, these two names gained currency in Germany before the object's existence was confirmed. Once it was, astronomers settled on Piazzi's name of 'Ceres'.[25]
The adjectival forms of 'Ceres' are Cererian[26][27] and Cererean,[28] both pronounced /sɪˈrɪəriən/.[29][30] The old astronomical symbol of Ceres is a sickle, ⟨⚳⟩,[31] one of the classical symbols of the goddess Ceres. In form it is similar to the symbol ⟨♀⟩ of the planet Venus, but with a break in the circle. It has a variant ⟨⚳⟩, reversed to resemble the initial letter 'C' of the name 'Ceres'. These symbols were later replaced with the generic asteroid symbol of a numbered disk, ⟨①⟩.[22][32] Cerium, a rare-earth element discovered in 1803, was named after Ceres.[33][b][c]
Classification
The categorization 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, at a distance of 419 million km (2.8 AU) from the Sun.[19] Ceres was assigned a planetary symbol, and remained listed as a planet in astronomy books and tables (along with Pallas, Juno, and Vesta) for half a century.[36]
As other objects were discovered in the neighborhood of Ceres, astronomers began to suspect that Ceres represented the first of a new class of objects.[19] In 1802, with the discovery of Pallas, Herschel coined the term asteroid ("star-like") for these bodies,[36] writing that "they resemble small stars so much as hardly to be distinguished from them, even by very good telescopes".[37] In 1852, astronomer Johann Franz Encke, in the Berliner Astronomisches Jahrbuch, declaring the traditional system of granting planetary symbols too cumbersome for these new objects, instead introduced a new system of placing numbers before their names in order of discovery. Initially, the numbering system began with the fifth asteroid, 5 Astraea, as number 1, but in 1867 Ceres was adopted into the new system under the name 1 Ceres.[36]
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.[36] Then, in 2006, the debate surrounding Pluto led to Ceres being considered for reclassification, perhaps even reinstatement as a planet.[38] A proposal before the International Astronomical Union (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".[39] Had this resolution been adopted, it would have made Ceres the fifth planet in order from the Sun;[40] but on 24 August 2006 the assembly adopted the additional requirement that a planet must have "cleared the neighborhood around its orbit". By this definition, 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 25% of the belt's total mass.[41] Bodies that met the first proposed definition but not the second, such as Ceres, were instead classified as dwarf planets.[41]
Since the IAU declaration in 2006 that Ceres is a dwarf planet, there has been some confusion as to whether it remains an asteroid. A NASA webpage declares that Vesta, the belt's second-largest object, is the largest asteroid.[42] The IAU has been equivocal on the subject,[43][44] though its Minor Planet Center, the organization charged with cataloguing such objects, notes that dwarf planets may have dual designations.[45]
Orbit
Ceres follows an orbit between Mars and Jupiter, within the asteroid belt and closer to the orbit of Mars, with an orbital period (year) of 4.6 Earth years.[2] Compared to other planets and dwarf planets, Ceres's orbit is moderately though not drastically tilted relative to Earth's orbit, with an orbital inclination (i) of 10.6° compared to 7° for Mercury and 17° for Pluto) and elongated, with an orbital eccentricity (e) = 0.08 compared to 0.09 for Mars).[2]
Ceres was once thought to be a member of the Gefion asteroid family.[46] 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 Gefion family,[46] and appears to be merely an interloper; coincidentally having similar orbital elements but not a common origin.[47] Ceres's lack of an asteroid family is believed to be due to the large proportion of ice in its makeup, which, if fragmented, would have sublimated to nothing over the age of the Solar System.[48]
Resonances
Due to their small masses and large separations, objects within the asteroid belt rarely fall into gravitational resonances with each other.[49] Nevertheless, Ceres is able to capture other asteroids into temporary 1:1 resonant orbital relationships (making them temporary trojans) for periods up to 2 million years or more; 50 such objects have been identified.[50] Ceres is in a near-1:1 mean-motion orbital resonance with Pallas (their proper orbital periods differ by 0.2%).[51]
Rotation and axial tilt
The rotation period of Ceres (the Cererian day) is 9 hours and 4 minutes. It has an axial tilt of 4°.[9] This is small 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 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 3 times before escaping or being trapped.[9]
Hubble Space Telescope observations in 2006 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°.[11] Dawn, the first spacecraft to orbit Ceres, determined that the north polar axis actually points at right ascension 19 h 25 m 40.3 s (291.418°), declination +66° 45' 50" (about 1.5 degrees from Delta Draconis), which means an axial tilt of 4°.[52]
Over the course of 3 million years, gravitational influence from Jupiter and Saturn has triggered cyclical shifts in Ceres's axial tilt, ranging from 2 to 20 degrees, meaning that seasonal effects have 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 their water over the age of the Solar System.[53]
Geology
Ceres is the largest asteroid in the main asteroid belt.[14] It has been classified both as a C-type or carbonaceous asteroid[14] and, due to the presence of clay minerals, as a G-type asteroid.[54] Its composition is similar, though not identical, to those of carbonaceous chondrite meteorites.[55] Ceres has a mean diameter of 939.4 km (583.7 mi)[2] and a mass of 9.39×1020 kg as determined from the Dawn spacecraft.[56] This gives it a density of 2.162±0.008 g/cm3,[2] suggesting a quarter of its mass is composed of water.[57] Ceres is an oblate spheroid, with an equatorial diameter 8% larger than its polar diameter.[2]
Ceres comprises approximately a quarter of the estimated total 3.0 ± 0.2×1021 kg mass of the asteroid belt,[41] or 1.3% of the mass of the Moon. Ceres is close to being in hydrostatic equilibrium, though some deviations from an equilibrium shape have yet to be fully explained.[58] Ceres is the smallest known dwarf planet, and the only dwarf planet inside the trans-Neptunian region.[57] Ceres is approximately the size of the large trans-Neptunian object Orcus.[59] Its surface area is approximately the same as the land area of India or Argentina.[60] Ceres is the smallest object likely to be in hydrostatic equilibrium, being 600 km (370 mi) smaller and less than half the mass of Saturn's moon Rhea, the next-smallest likely object.[61] Modeling has suggested Ceres could have a small metallic core from partial differentiation of its rocky fraction,[62][63] but the data are consistent with a mantle of hydrated silicates and no core.[58]
Surface
Composition
The surface composition of Ceres is homogeneous on a global scale, and is rich in carbonates and ammoniated phyllosilicates that have been altered by water,[58] though water ice in the regolith varies from approximately 10% in polar latitudes to much drier, even ice-free, in the equatorial regions.[58]
Studies using the Hubble Space Telescope reveal that graphite, sulfur, and sulfur dioxide are present 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 are evidently associated with areas with relatively recent geological activity.[64]
Tholins, formed from ultraviolet irradiation of simple carbon compounds, were detected on Ceres in Ernutet crater,[65] and most of the planet's near surface is extremely rich in carbon, at approximately 20% by mass.[66] The carbon content is more than five times higher than in carbonaceous chondrite meteorites analyzed on Earth.[66] The surface carbon shows evidence of being mixed with products of rock-water interactions, such as clays.[66] 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 favorable to organic chemistry.[66]
Craters
Dawn revealed that Ceres has a heavily cratered surface; though with fewer large craters than expected.[69] Models based on the formation of the current asteroid belt had suggested Ceres should possess 10 to 15 craters larger than 400 km (250 mi) in diameter.[69] The largest confirmed crater on Ceres, Kerwan Basin, is just 284 km (176 mi) across.[70] The most likely reason for this is viscous relaxation of the crust slowly flattening out earlier impacts.[69]
Ceres's north polar region shows far more cratering than the equatorial region, with the eastern hemisphere in particular comparatively lightly cratered. The size frequency of craters of between 20 and 100 km (12 and 60 mi) is consistent with them having originated in the Late Heavy Bombardment, with craters outside the ancient polar regions likely erased by early cryovolcanism.[71] Three large shallow basins (planitiae) with degraded rims, are also likely eroded craters.[58] The largest, Vendimia Planitia, at 800 km (500 mi) across,[69] is also the largest single geographical feature on Ceres.[72] Two of the three have higher than average ammonium concentrations.[58]
Cryovolcanism
Ceres has one prominent mountain, Ahuna Mons; this peak appears to be a cryovolcano and has few craters, suggesting a maximum age of no more than 240 million years.[74] 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 of a slurry of brine and silicate particles from the top of the mantle.[48] It is roughly antipodal to Kerwan, the largest confirmed impact basin on Ceres. Seismic energy from the Kerwan-forming impact may have focused on the opposite side of Ceres, fracturing the outer layers of the crust and facilitating the movement of high-viscosity cryomagma (consisting of muddy water ice softened by its content of salts) onto the surface.[75] Kerwan too shows evidence of the effects of liquid water due to impact melting of subsurface ice.[70]
A 2018 computer simulation suggested that cryovolcanoes on Ceres have fallen back due to viscous relaxation over the course of roughly the last billion years. The team identified 22 features as strong candidates for relaxed cryovolcanoes on Ceres's surface.[74][76] Yamor Mons, an ancient, impact-cratered peak, resembles Ahuna Mons despite showing no signs of recent activity, due to it lying in Ceres's northern polar region, where colder temperatures prevent viscous relaxation of the crust.[77] Models suggest that one cryovolcano has formed on Ceres on average every 50 million years.[77] The model suggests that, contrary to findings at Ahuna Mons, Cerean cryovolcanoes must be composed of far less dense material than average for Ceres's crust, or the observed viscious relaxation could not occur.[74]
An unexpectedly large number of Cererian craters have central pits, perhaps due to cryovolcanic processes, whilst others have central peaks.[78] Hundreds of bright spots (faculae) have been observed by Dawn, the brightest located in the middle of an 80 km (50 mi) crater called Occator.[79] The spot in the center of Occator is named Cerealia Facula,[80] and the group of spots to its east, Vinalia Faculae.[81] A haze periodically appears above Cerealia, supporting the hypothesis that some sort of outgassing or sublimating ice formed the bright spots.[82] In March 2016, Dawn found definitive evidence of water molecules on the surface of Ceres at Oxo crater.[83]
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.[84] Near-infrared spectra of these bright areas were reported in 2017 to be consistent with a large amount of sodium carbonate (Na
2CO
3) and smaller amounts of ammonium chloride (NH
4Cl) or ammonium bicarbonate (NH
4HCO
3).[85][86] These materials have been suggested to originate from the crystallization of brines that reached the surface from below.[87] 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[88] causing "bright spots", including those in Occator crater.[89] NASA compared Cerealia dome to pingos in Earth's Arctic region; distended eruptions from the surface caused by expanding freezing water beneath.[90]
Tectonic features
Although Ceres lacks plate tectonics,[77] with the vast majority of its surface features linked either to impacts or to cryovolcanic activity, several potentially tectonic features have been tentatively identified on Ceres, particularly in its eastern hemisphere. The Samhain Catenae, kilometer-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 faults. Also, several craters on Ceres have shallow, fractured floors consistent with cryomagmatic intrusion.[91]
Boulders
Dawn has observed 4,423 boulders larger than 105 m (344 ft) on the surface of Ceres. These boulders are likely formed through impacts, and thus are found within or near craters, though not all craters contain boulders. Vast regions of the surface of Ceres lack any craters larger than 100 m (330 ft). In addition, the large boulders on Ceres are more numerous at higher latitudes than at lower latitudes. These boulders 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 150 million years, which is much shorter than the lifetime of boulders on Vesta.[92]
Internal structure
The active geology of Ceres is driven by ice and brines. Water leached from rock is estimated to possess salinity of around 5%. Altogether, Ceres is approximately 40% or 50% water by volume, compared to 0.1% for Earth, and 73% rock by mass.[12]
The fact that the surface has preserved craters smaller than 300 km (190 mi) in diameter indicates that the outermost layer of Ceres is on the order of 1000 times stronger than water ice. This is consistent with a mixture of silicates, hydrated salts and methane clathrates, with no more than approximately 30% water ice.[58]
Gravity measurements from Dawn have generated three competing models for Ceres's interior.[12] In the three-layer model, Ceres is thought to consist of an inner muddy mantle of hydrated rock, such as clays, an intermediate layer comprising a muddy mixture of brine and rock down to a depth of at least 100 km (62 mi), and an outer, 40 km (25 mi) thick crust of ice, salts and hydrated minerals.[93] It is not possible to tell if Ceres' deep interior contains liquid or a core of dense material rich in metal,[94] but the low central density suggests it may retain about 10% porosity.[12] One study estimated the densities of the core and mantle/crust to be 2.46–2.90 and 1.68–1.95 g/cm3 respectively, with the mantle and crust being 70–90 km (43–56 mi) 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.[8] That is, the core, mantle and crust all consist of rock and ice, though in different ratios.
The mineral composition can only be determined indirectly for the outer 100 km (62 mi). The 40 km (25 mi) thick solid outer crust 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 100 km (62 mi) limit of detection. Under that is thought to be a mantle dominated by hydrated rocks such as clays.[94]
In one two-layer model, Ceres consists of a core of chondrules 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 20 meters thick. The range of the extent of differentiation is consistent with the data, from a large, 360 km (220 mi) core of 75% chondrules and 25% particulates and a mantle of 75% ice and 25% particulates, to a small, 85 km (53 mi) 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 110 km (68 mi). In the latter case, a 2% freezing of the liquid reservoir would compress the liquid enough to force some to the surface, producing cryovolcanism.[95]
A second two-layer model notes that Dawn data is consistent with 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 70 km (43 mi) thick and have a density of 1.68 g/cm3; with CM-class meteorites (density 2.9 g/cm3), the crust would be approximately 190 km (120 mi) thick and have a density of 1.9 g/cm3. Best-fit modeling yields a crust approximately 40 km (25 mi) thick with a density of approximately 1.25 g/cm3, and a mantle/core density of approximately 2.4 g/cm3.[58]
Atmosphere
In 2017, Dawn confirmed that Ceres has a transient atmosphere of water vapor derived from exposed surface ice evaporated by the Sun.[96] Hints of an atmosphere had appeared in early 2014, when the Herschel Space Observatory detected localized mid-latitude sources of water vapor on Ceres, no more than 60 km (37 mi) in diameter, which each give off approximately 1026 molecules (or 3 kg) of water per second.[97][98][d] Two potential source regions, designated Piazzi (123°E, 21°N) and Region A (231°E, 23°N), were visualized in the near infrared as dark areas (Region A also has a bright center) by the Keck Observatory. Possible mechanisms for the vapor release are sublimation from approximately 0.6 km2 (0.23 sq mi) of exposed surface ice, or cryovolcanic eruptions resulting from radiogenic internal heat[97] or from pressurization of a subsurface ocean due to growth of an overlying layer of ice.[101] In 2015, David Jewitt included Ceres in his list of active asteroids.[102] Surface water ice is unstable at distances less than 5 AU from the Sun,[103] 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 short time. Surface sublimation would be expected to be lower when Ceres is farther from the Sun in its orbit, whereas internally powered emissions should not be affected by its orbital position. The limited data previously available was more consistent with cometary-style sublimation,[97] though subsequent evidence from Dawn strongly suggests ongoing geologic activity could be at least partially responsible.[104]
Studies using Dawn's gamma ray and neutron detector (GRaND) reveal that Ceres is accelerating electrons from the solar wind regularly; the most accepted hypothesis is that these electrons are being accelerated by collisions between the solar wind and a tenuous water vapor exosphere.[105]
Origin and evolution
Ceres is a surviving protoplanet that formed 4.56 billion years ago, the only one in the inner Solar System, with the rest either merging to form terrestrial planets or being ejected from the Solar System by Jupiter.[106] Despite this, its composition is not consistent with a formation within the asteroid belt. It seems rather that Ceres formed as a centaur, a minor planet between the orbits of Jupiter and Saturn, and was scattered into the asteroid belt as Jupiter migrated outward.[12] The discovery of ammonia salts in Occator crater supports an origin in the outer Solar System, as ammonia is far more abundant in that region.[107]
The early geological evolution of Ceres was dependent on the heat sources available during and after its formation: friction from planetesimal accretion, and decay of radionuclides (possibly including short-lived extinct radionuclides such as aluminium-26). These are thought to have been sufficient to allow Ceres to differentiate into a rocky core and icy mantle soon after its formation,[63] possibly even a liquid water ocean.[58] This water 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.[58]
Ceres possesses a surprisingly small number of large craters, suggesting that viscous relaxation and cryovolcanism may have erased older geological features.[108] The presence of clays and carbonates requires chemical reactions in temperatures above 50 °C, consistent with hydrothermal activity.[48]
Ceres 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, in stark contrast to Vesta[109] and of previous expectations that Ceres would have become geologically dead early in its history due to its small size.[110]
Potential habitability
Although Ceres is not as actively discussed as a potential home for microbial extraterrestrial life as Mars, Europa, Enceladus, or Titan are, it is the most water-rich body in the inner Solar System after Earth,[48] and there is evidence that its icy mantle was once a watery subterranean ocean.[66] Although it does not experience tidal heating, like Europa or Enceladus, it is close enough to the Sun, and contains enough long-lived radioactive isotopes, to preserve liquid water in its subsurface for extended periods.[48] The remote detection of organic compounds and the presence of water with 20% carbon by mass in its near surface could provide conditions favorable to organic chemistry.[66] Ceres is rich in carbon, hydrogen, oxygen and nitrogen, but the two other crucial biogenic elements, sulfur and phosphorus, have proven elusive.[48][111] The likely brine pockets under its surface could provide habitats for life.[48]
Observation and exploration
Observation
When in opposition near its perihelion, Ceres can reach an apparent magnitude of +6.7.[112] This is too dim to be visible to the average naked eye, but under ideal viewing conditions, keen eyes with 20/20 vision may be able to see it. The only other asteroids that can reach a similarly bright magnitude are Vesta and, when in rare oppositions near their perihelions, Pallas and 7 Iris.[113] 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.[15]
On 13 November 1984, an occultation of the star BD+8°471 by Ceres was observed in Mexico, Florida and across the Caribbean, allowing better measurements of its size, shape and albedo.[114] On 25 June 1985, Hubble attained ultraviolet images of Ceres with 50 km (31 mi) resolution.[54] In 2002, the Keck Observatory attained infrared images with 30 km (19 mi) resolution using adaptive optics.[115]
Before the Dawn mission, only a few surface features had been unambiguously detected on Ceres. High-resolution ultraviolet Hubble images taken in 1995 showed a spot on its surface, which was nicknamed "Piazzi" in honor of the discoverer of Ceres.[54] This was thought to be a crater. The higher-resolution near-infrared images taken over a whole rotation with the Keck Observatory in 2012 using adaptive optics showed bright and dark features moving with Ceres' rotation.[116] Two dark features had circular shapes and were presumed to be craters; one of them was observed to have a bright central region, whereas another was identified as the "Piazzi" feature.[116] Visible-light Hubble Space Telescope images of a full rotation taken in 2003 and 2004 showed 11 recognizable surface features, the natures of which were then undetermined.[11][117] One of these features corresponds to the "Piazzi" feature observed earlier.[11] Dawn would eventually reveal "Piazzi" to be a dark spot in the middle of Vendimia Planitia, close to crater Dantu.[118]
Proposed exploration
In 1981, a proposal for an asteroid mission was submitted to the European Space Agency (ESA). Named the Asteroidal Gravity Optical and Radar Analysis (AGORA), this spacecraft was to launch some time in 1990–1994 and perform two flybys of large asteroids. The preferred target for this mission was Vesta. AGORA would reach the asteroid belt either by a gravitational slingshot trajectory past Mars or by means of a small ion engine. That proposal was refused by ESA. A joint NASA–ESA asteroid mission was then drawn up for a Multiple Asteroid Orbiter with Solar Electric Propulsion (MAOSEP), with one of the mission profiles including an orbit of Vesta. NASA indicated they were not interested in an asteroid mission. Instead, ESA set up a technological study of a spacecraft with an ion drive. Other missions to the asteroid belt were proposed in the 1980s by France, Germany, Italy, and the United States, but none were approved.[119]
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 recommended as a high priority a mission to explore the asteroid belt using a spacecraft with an ion engine. Funding for this program remained problematic for nearly a decade, but by 2004 the Dawn vehicle had passed its critical design review.[120]
It was launched on 27 September 2007, as the space mission to make the first visits to both Vesta and Ceres. On 3 May 2011, Dawn acquired its first targeting image 1,200,000 km (750,000 mi) from Vesta.[121] After orbiting Vesta for 13 months, Dawn used its ion engine to depart for Ceres, with gravitational capture occurring on 6 March 2015[122] at a separation of 61,000 km (38,000 mi),[123] four months prior to the New Horizons flyby of Pluto.[123]
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 13,500 km (8,400 mi) on 23 April 2015, staying for only approximately one orbit (15 days).[124][125] The spacecraft subsequently reduced its orbital distance to 4,400 km (2,700 mi) for its second observational orbit ("survey") for three weeks,[126] then down to 1,470 km (910 mi) ("HAMO;" high altitude mapping orbit) for two months[127] and then down to its final orbit at 375 km (233 mi) ("LAMO;" low altitude mapping orbit) for at least three months.[128]
The spacecraft instrumentation includes a framing camera, a visual and infrared spectrometer, and a gamma-ray and neutron detector. These instruments examined Ceres' shape and elemental composition.[129] On 13 January 2015, Dawn took the first images of Ceres at near-Hubble resolution, revealing impact craters and a small high-albedo spot on the surface, near the same location as that observed previously. Additional imaging sessions, at increasingly better resolution took place on 25 January; 4, 12, 19 and 25 February; 1 March, and 10 and 15 April.[130] In October 2015, NASA released a true-color portrait of Ceres made by Dawn.[131]
Pictures with a resolution previously unattained were taken during imaging sessions starting in January 2015 as Dawn approached Ceres, showing a cratered surface. Two distinct bright spots (or high-albedo features) inside a crater (different from the bright spots observed in earlier Hubble images)[132] were seen in a 19 February 2015 image, leading to speculation about a possible cryovolcanic origin[133] or outgassing.[134] On 2 September 2016, scientists from the Dawn team argued in a Science paper that Ahuna Mons was the strongest evidence yet for cryovolcanic features.[75] On 11 May 2015, NASA released a higher-resolution image showing that the spots were actually composed of multiple smaller spots.[135] 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.[84] In June 2016, near-infrared spectra of these bright areas were found to be consistent with a large amount of sodium carbonate (Na
2CO
3), implying that recent geologic activity was probably involved in the creation of the bright spots.[136] From June to October 2018, Dawn orbited Ceres from as close as 35 km (22 mi) and as far away as 4,000 km (2,500 mi).[137] The Dawn mission ended on 1 November 2018 after the spacecraft ran out of fuel.[138]
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.[65] The Chinese Space Agency is designing a sample-return mission from Ceres that would take place during the 2020s.[139]
Maps
Dawn's operational lifetime around Ceres lasted 3 years, allowing for its entire surface to be mapped.
Map of Ceres (Elliptical; HAMO; color; March 2016) |
Black-and-white photographic map of Ceres, centered on 180° longitude, with official nomenclature (September 2017) |
Ceres, polar regions (November 2015): North (left); south (right). "Ysolo Mons" has been renamed "Yamor Mons."[68] |
See also
- Asteroid Ceres in fiction
- List of exceptional asteroids
- List of Solar System objects by size
- Asteroid mining
Notes
- ^ The value given for Ceres is the mean moment of inertia, which is thought to better represent its interior structure than the polar moment of inertia, due to its high polar flattening.[8]
- ^ In 1807 Klaproth tried to change the name of the element to 'cererium', to avoid confusion with the root cēra 'wax' (as in cereous 'waxy'), but it did not catch on.[34]
- ^ A notebook of the discoverer of a palladium, another new element, William Hyde Wollaston, abbreviates that element as 'C', which Wollaston would later explaine as probably being for 'Ceresium', a name which he had thought to name the element.[35]
- ^ This emission rate is modest compared to those calculated for the tidally driven plumes of Enceladus (a smaller body) and Europa (a larger body), 200 kg/s[99] and 7000 kg/s,[100] respectively.
References
- ^ Schmadel, Lutz (2003). Dictionary of minor planet names (5th ed.). Germany: Springer. p. 15. ISBN 978-3-540-00238-3.
- ^ a b c d e f g h i j k l "1 Ceres". JPL Small-Body Database Browser. Retrieved 8 September 2019.
- ^ Souami, D.; Souchay, J. (July 2012). "The solar system's invariable plane". Astronomy & Astrophysics. 543: 11. Bibcode:2012A&A...543A.133S. doi:10.1051/0004-6361/201219011. A133.
- ^ "AstDyS-2 Ceres Synthetic Proper Orbital Elements". Department of Mathematics, University of Pisa, Italy. Archived from the original on 5 October 2011. Retrieved 1 October 2011.
- ^ a b "Asteroid Ceres P_constants (PcK) SPICE kernel file". Retrieved 8 September 2019.
- ^ a b c d e Calculated based on the known parameters
- Surface area: 4πr2
- Volume: 4/3πr3
- Surface gravity: GM/r2
- Escape velocity: √2GM/r
- Rotation velocity: rotation period/circumference
- ^ Mao, X.; McKinnon, W. B. (2018). "Faster paleospin and deep-seated uncompensated mass as possible explanations for Ceres' present-day shape and gravity". Icarus. 299: 430–442. Bibcode:2018Icar..299..430M. doi:10.1016/j.icarus.2017.08.033.
- ^ a b Park, R. S.; Konopliv, A. S.; Bills, B. G.; Rambaux, N.; Castillo-Rogez, J. C.; Raymond, C. A.; Vaughan, A. T.; Ermakov, A. I.; Zuber, M. T.; Fu, R. R.; Toplis, M. J.; Russell, C. T.; Nathues, A.; Preusker, F. (3 August 2016). "A partially differentiated interior for (1) Ceres deduced from its gravity field and shape". Nature. 537 (7621): 515–517. Bibcode:2016Natur.537..515P. doi:10.1038/nature18955. PMID 27487219. S2CID 4459985.
- ^ a b c Schorghofer, N.; Mazarico, E.; Platz, T.; Preusker, F.; Schröder, S. E.; Raymond, C. A.; Russell, C. T. (6 July 2016). "The permanently shadowed regions of dwarf planet Ceres". Geophysical Research Letters. 43 (13): 6783–6789. Bibcode:2016GeoRL..43.6783S. doi:10.1002/2016GL069368.
- ^ Konopliv, A.S.; Park, R.S.; Vaughan, A.T.; Bills, B.G.; Asmar, S.W.; Ermakov, A.I.; Rambaux, N.; Raymond, C.A.; Castillo-Rogez, J.C.; Russell, C.T.; Smith, D.E.; Zuber, M.T. (2018). "The Ceres gravity field, spin pole, rotation period and orbit from the Dawn radiometric tracking and optical data". Icarus. 299: 411–429. Bibcode:2018Icar..299..411K. doi:10.1016/j.icarus.2017.08.005.
- ^ a b c d Li, Jian-Yang; McFadden, Lucy A.; Parker, Joel Wm. (2006). "Photometric analysis of 1 Ceres and surface mapping from HST observations". Icarus. 182 (1): 143–160. Bibcode:2006Icar..182..143L. doi:10.1016/j.icarus.2005.12.012.
- ^ a b c d e JC Castillo Rogez; CA Raymond; CT Russell; Dawn Team (2017). "Dawn at Ceres: What Have We Learned?" (PDF). NASA, JPL. Retrieved 19 July 2021.
- ^ "Surface temperature of dwarf planet Ceres: Preliminary results from Dawn" (PDF).
- ^ a b c Rivkin, A. S.; Volquardsen, E. L.; Clark, B. E. (2006). "The surface composition of Ceres: Discovery of carbonates and iron-rich clays" (PDF). Icarus. 185 (2): 563–567. Bibcode:2006Icar..185..563R. doi:10.1016/j.icarus.2006.08.022. Retrieved 8 December 2007.
- ^ a b "Dwarf Planet 1 Ceres Information". TheSkyLive.com. Retrieved 26 November 2017.
- ^ "Asteroid (1) Ceres – Summary". AstDyS-2, Asteroids – Dynamic Site. Retrieved 15 October 2019.
- ^ "Ceres". Dictionary.com Unabridged (Online). n.d.
- ^ Val Dusek (1999). The Holistic Inspirations of Physics: The Underground History of Electromagnetic Theory. Rutgers University Press. pp. 175–176.
- ^ a b c d e f g h i Hoskin, Michael (26 June 1992). "Bode's Law and the Discovery of Ceres". Observatorio Astronomico di Palermo "Giuseppe S. Vaiana". Archived from the original on 18 January 2010. Retrieved 5 July 2007.
- ^ a b c d e Hogg, Helen Sawyer (1948). "The Titius-Bode Law and the Discovery of Ceres". Journal of the Royal Astronomical Society of Canada. 242: 241–246. Bibcode:1948JRASC..42..241S.
- ^ Landau, Elizabeth (26 January 2016). "Ceres: Keeping Well-Guarded Secrets for 215 Years". NASA. Retrieved 26 January 2016.
- ^ a b c d e f Forbes, Eric G. (1971). "Gauss and the Discovery of Ceres". Journal for the History of Astronomy. 2 (3): 195–199. Bibcode:1971JHA.....2..195F. doi:10.1177/002182867100200305. S2CID 125888612.
- ^ Cunningham, Clifford J. (2001). The first asteroid: Ceres, 1801–2001. Star Lab Press. ISBN 978-0-9708162-1-4.
- ^ a b Hughes, David W (1994). "The Historical Unravelling of the Diameters of the First Four Asteroids". Quarterly Journal fo the Royal Astronomical Society. 35: 331–344.
- ^ Foderà Serio, G.; Manara, A.; Sicoli, P. (2002). "Giuseppe Piazzi and the Discovery of Ceres" (PDF). In W. F. Bottke Jr.; A. Cellino; P. Paolicchi; R. P. Binzel (eds.). Asteroids III. Tucson, Arizona: University of Arizona Press. pp. 17–24. Retrieved 25 June 2009.
- ^ Rüpke, Jörg (2011). A Companion to Roman Religion. John Wiley and Sons. pp. 90–. ISBN 978-1-4443-4131-7.
- ^ "Dawn Spacecraft Finds Traces of Water on Vesta," Sci-Tech Daily, 21 September 2012
- ^ Rivkin et al. (2012) "The Surface Composition of Ceres," in Christopher Russell & Carol Raymond, eds., The Dawn Mission to Minor Planets 4 Vesta and 1 Ceres, p. 109.
- ^ William Thomas Thornton (1878) "Epode 16", Word for word from Horace, page 314
- ^ E.g. Booth (1923) Flowers of Roman poesy
- ^ Unicode value U+26B3
- ^ Gould, B. A. (1852). "On the symbolic notation of the asteroids". Astronomical Journal. 2 (34): 80. Bibcode:1852AJ......2...80G. doi:10.1086/100212.
- ^ "Cerium: historical information". Adaptive Optics. Retrieved 27 April 2007.
- ^ "Cerium". Oxford English Dictionary (Online ed.). Oxford University Press. (Subscription or participating institution membership required.)
- ^ "William Hyde Wollaston: The Production of Malleable Platinum". Platinum Metals Review. 10 (3): 101. 1966.
- ^ a b c d Hilton, James L. (17 September 2001). "When Did the Asteroids Become Minor Planets?". Archived from the original on 6 November 2007. Retrieved 16 August 2006.
- ^ Herschel, William (6 May 1802). "Observations on the two lately discovered celestial Bodies". Philosophical Transactions of the Royal Society of London. 92: 213–232. Bibcode:1802RSPT...92..213H. doi:10.1098/rstl.1802.0010. JSTOR 107120. S2CID 115664950.
- ^ Connor, Steve (16 August 2006). "Solar system to welcome three new planets". NZ Herald.
{{cite news}}
:|archive-date=
requires|archive-url=
(help)CS1 maint: url-status (link) - ^ Gingerich, Owen; et al. (16 August 2006). "The IAU draft definition of "Planet" and "Plutons"". IAU. Archived from the original on 5 October 2011. Retrieved 27 April 2007.
- ^ "The IAU Draft Definition of Planets And Plutons". SpaceDaily. 16 August 2006. Archived from the original on 18 January 2010. Retrieved 27 April 2007.
- ^ a b c "In Depth | Ceres". NASA Solar System Exploration.
- ^ "Science: One Mission, Two Remarkable Destinations". NASA. Retrieved 14 July 2020.
Asteroids range in size from Vesta — the largest at about 329 miles (530 km) in diameter...
- ^ Lang, Kenneth (2011). The Cambridge Guide to the Solar System. Cambridge University Press. pp. 372, 442. ISBN 978-1-139-49417-5.
- ^ "Question and answers 2". IAU. Retrieved 31 January 2008.
Ceres is (or now we can say it was) the largest asteroid" ... "There are many other asteroids that can come close to the orbital path of Ceres.
- ^ Spahr, T. B. (7 September 2006). "MPEC 2006-R19: EDITORIAL NOTICE". Minor Planet Center. Archived from the original on 10 October 2008. Retrieved 31 January 2008.
the numbering of "dwarf planets" does not preclude their having dual designations in possible separate catalogues of such bodies.
- ^ a b Cellino, A.; et al. (2002). "Spectroscopic Properties of Asteroid Families" (PDF). Asteroids III. University of Arizona Press. pp. 633–643 (Table on p. 636). Bibcode:2002aste.book..633C.
- ^ Kelley, M. S.; Gaffey, M. J. (1996). "A Genetic Study of the Ceres (Williams #67) Asteroid Family". Bulletin of the American Astronomical Society. 28: 1097. Bibcode:1996DPS....28.1009K.
- ^ a b c d e f g Julie C. Castillo-Rogez; et al. (31 January 2020). "Ceres: Astrobiological Target and Possible Ocean World". Astrobiology. 20 (2). doi:10.1089/ast.2018.1999.
- ^ Christou, A. A. (2000). "Co-orbital objects in the main asteroid belt". Astronomy and Astrophysics. 356: L71–L74. Bibcode:2000A&A...356L..71C.
- ^ Christou, A. A.; Wiegert, P. (January 2012). "A population of Main Belt Asteroids co-orbiting with Ceres and Vesta". Icarus. 217 (1): 27–42. arXiv:1110.4810. Bibcode:2012Icar..217...27C. doi:10.1016/j.icarus.2011.10.016. ISSN 0019-1035. S2CID 59474402.
- ^ Kovačević, A. B. (2011). "Determination of the mass of Ceres based on the most gravitationally efficient close encounters". Monthly Notices of the Royal Astronomical Society. 419 (3): 2725–2736. arXiv:1109.6455. Bibcode:2012MNRAS.419.2725K. doi:10.1111/j.1365-2966.2011.19919.x.
- ^ "05. Dawn Explores Ceres Results from the Survey Orbit" (PDF). Archived from the original (PDF) on 5 September 2015.
- ^ "Ice in Ceres' Shadowed Craters Linked to Tilt History". NASA Solar System Exploration. 2017. Retrieved 15 May 2021.
- ^ a b c Parker, J. W.; Stern, Alan S.; Thomas Peter C.; et al. (2002). "Analysis of the first disk-resolved images of Ceres from ultraviolet observations with the Hubble Space Telescope". The Astronomical Journal. 123 (1): 549–557. arXiv:astro-ph/0110258. Bibcode:2002AJ....123..549P. doi:10.1086/338093. S2CID 119337148.
- ^ Thomas B. McCord, Francesca Zambon (15 January 2019). "The surface composition of Ceres from the Dawn mission". Icarus. 318: 2–13.
- ^ Rayman, Marc D. (28 May 2015). "Dawn Journal, 28 May 2015". Jet Propulsion Laboratory. Archived from the original on 30 May 2015. Retrieved 29 May 2015.
- ^ a b Nola Taylor Redd (23 May 2018). "Ceres: The Smallest and Closest Dwarf Planet". space.com. Retrieved 25 July 2021.
- ^ a b c d e f g h i j Raymond, C.; Castillo-Rogez, J.C.; Park, R.S.; Ermakov, A.; et al. (September 2018). "Dawn Data Reveal Ceres' Complex Crustal Evolution" (PDF). European Planetary Science Congress. Vol. 12.
- ^ Brown, Michael E.; Butler, Bryan J. (22 January 2018). "Medium-sized satellites of large Kuiper belt objects". The Astronomical Journal. 156 (4): 164. arXiv:1801.07221. doi:10.3847/1538-3881/aad9f2.
{{cite journal}}
: CS1 maint: unflagged free DOI (link) - ^ Approximately 40% that of Australia, a third the size of the US or Canada, 12× that of the UK
- ^ Thomas, P. C. (July 2010). "Sizes, shapes, and derived properties of the saturnian satellites after the Cassini nominal mission" (PDF). Icarus. 208 (1): 395–401. Bibcode:2010Icar..208..395T. doi:10.1016/j.icarus.2010.01.025.
- ^ Neumann, W.; Breuer, D.; Spohn, T. (2 December 2015). "Modelling the internal structure of Ceres: Coupling of accretion with compaction by creep and implications for the water-rock differentiation" (PDF). Astronomy & Astrophysics. 584: A117. Bibcode:2015A&A...584A.117N. doi:10.1051/0004-6361/201527083.
- ^ a b Bhatia, G.K.; Sahijpal, S. (2017). "Thermal evolution of trans-Neptunian objects, icy satellites, and minor icy planets in the early solar system". Meteoritics & Planetary Science. 52 (12): 2470–2490. Bibcode:2017M&PS...52.2470B. doi:10.1111/maps.12952.
- ^ "Sulfur, Sulfur Dioxide, Graphitized Carbon Observed on Ceres". spaceref.com. 3 September 2016. Retrieved 8 September 2016.
- ^ a b L. E. Kissick; G. Acciarini; H. Bates; et al. (2020). "Sample Return From A Relic Ocean World: The Calthus Mission To Occator Crater, Ceres" (PDF). 51st Lunar and Planetary Science Conference.
- ^ a b c d e f Marchi, S.; Raponi, A.; Prettyman, T. H.; De Sanctis, M. C.; Castillo-Rogez, J.; Raymond, C. A.; Ammannito, E.; Bowling, T.; Ciarniello, M.; Kaplan, H.; Palomba, E.; Russell, C. T.; Vinogradoff, V.; Yamashita, N. (2018). "An aqueously altered carbon-rich Ceres". Nature Astronomy. 3 (2): 140–145. doi:10.1038/s41550-018-0656-0. S2CID 135013590.
- ^ Landau, Elizabeth (28 July 2015). "New Names and Insights at Ceres". NASA. Retrieved 28 July 2015.
- ^ a b "Name Changed on Ceres". USGS. 7 December 2016. Retrieved 19 August 2021.
- ^ a b c d Marchi, S.; Ermakov, A. I.; Raymond, C. A.; Fu, R. R.; O'Brien, D. P.; Bland, M. T.; Ammannito, E.; De Sanctis, M. C.; Bowling, T.; Schenk, P.; Scully, J. E. C.; Buczkowski, D. L.; Williams, D. A.; Hiesinger, H.; Russell, C. T. (26 July 2016). "The missing large impact craters on Ceres". Nature Communications. 7: 12257. Bibcode:2016NatCo...712257M. doi:10.1038/ncomms12257. PMC 4963536. PMID 27459197.
- ^ a b David A. Williams, T. Kneiss (December 2018). "The geology of the Kerwan quadrangle of dwarf planet Ceres: Investigating Ceres' oldest, largest impact basin". Icarus. 316: 99–113.
- ^ Strom, R.G., S. Marchi and R. Malhotra (2018). "Ceres and the Terrestrial Planets Impact Cratering Record" (PDF). Icarus. 302: 104–108.
{{cite journal}}
: CS1 maint: multiple names: authors list (link) - ^ "Hanami Planum on Ceres". NASA. 23 March 2018. Retrieved 17 August 2021.
- ^ "PIA20348: Ahuna Mons Seen from LAMO". Jet Propulsion Lab. 7 March 2016. Retrieved 14 April 2016.
- ^ a b c Michael T. Sori, Hanna G. Sizemore; et al. (December 2018). "Cryovolcanic rates on Ceres revealed by topography". Nature Astronomy. 2: 946–950.
- ^ a b Ruesch, O.; Platz, T.; Schenk, P.; McFadden, L. A.; Castillo-Rogez, J. C.; Quick, L. C.; Byrne, S.; Preusker, F.; OBrien, D. P.; Schmedemann, N.; Williams, D. A.; Li, J.- Y.; Bland, M. T.; Hiesinger, H.; Kneissl, T.; Neesemann, A.; Schaefer, M.; Pasckert, J. H.; Schmidt, B. E.; Buczkowski, D. L.; Sykes, M. V.; Nathues, A.; Roatsch, T.; Hoffmann, M.; Raymond, C. A.; Russell, C. T. (2 September 2016). "Cryovolcanism on Ceres". Science. 353 (6303): aaf4286. Bibcode:2016Sci...353.4286R. doi:10.1126/science.aaf4286. PMID 27701087.
- ^ Sori, Michael M.; Byrne, Shane; Bland, Michael T.; Bramson, Ali M.; Ermakov, Anton I.; Hamilton, Christopher W.; Otto, Katharina A.; Ruesch, Ottaviano; Russell, Christopher T. (2017). "The vanishing cryovolcanoes of Ceres" (PDF). Geophysical Research Letters. 44 (3): 1243–1250. Bibcode:2017GeoRL..44.1243S. doi:10.1002/2016GL072319. hdl:10150/623032.
- ^ a b c "Ceres takes life an ice volcano at a time". University of Arizona. 17 September 2018. Retrieved 22 April 2019.
- ^ "News – Ceres Spots Continue to Mystify in Latest Dawn Images". NASA/JPL.
- ^ "USGS: Ceres nomenclature" (PDF). Retrieved 16 July 2015.
- ^ "Cerealia Facula". Gazetteer of Planetary Nomenclature. USGS Astrogeology Research Program.
- ^ "Vinalia Faculae". Gazetteer of Planetary Nomenclature. USGS Astrogeology Research Program.
- ^ Rivkin, Andrew (21 July 2015). "Dawn at Ceres: A haze in Occator crater?". The Planetary Society. Retrieved 8 March 2017.
- ^ Redd, Nola Taylor. "Water Ice on Ceres Boosts Hopes for Buried Ocean [Video]". Scientific American. Retrieved 7 April 2016.
- ^ a b Landau, Elizabeth (9 December 2015). "New Clues to Ceres' Bright Spots and Origins". phys.org. Retrieved 10 December 2015.
- ^ Preferential formation of sodium salts from frozen sodium-ammonium-chloride-carbonate brines – Implications for Ceres' bright spots. Tuan H. Vu, Robert Hodyss, Paul V. Johnson, Mathieu Choukroun. Planetary and Space Science, Volume 141, July 2017, Pages 73–77
- ^ McCord, Thomas B.; Zambon, Francesca (2019). "The surface composition of Ceres from the Dawn mission". Icarus. 318: 2–13. Bibcode:2019Icar..318....2M. doi:10.1016/j.icarus.2018.03.004.
- ^ Quick, Lynnae C.; Buczkowski, Debra L.; Ruesch, Ottaviano; Scully, Jennifer E. C.; Castillo-Rogez, Julie; Raymond, Carol A.; Schenk, Paul M.; Sizemore, Hanna G.; Sykes, Mark V. (1 March 2019). "A Possible Brine Reservoir Beneath Occator Crater: Thermal and Compositional Evolution and Formation of the Cerealia Dome and Vinalia Faculae". Icarus. 320: 119–135. Bibcode:2019Icar..320..119Q. doi:10.1016/j.icarus.2018.07.016.
- ^ N.T. Stein; B.L. Ehlmann (1 March 2019). "The formation and evolution of bright spots on Ceres". Icarus. 320: 188–201. doi:10.1016/j.icarus.2017.10.014.
- ^ McCartney, Gretchen (11 August 2020). "Mystery solved: Bright areas on Ceres come from salty water below". Phys.org. Retrieved 12 August 2020.
- ^ Landau, Elizabeth; McCartney, Gretchen (24 July 2018). "What Looks Like Ceres on Earth?". NASA. Retrieved 26 July 2021.
- ^ Buczkowski, D. ; Scully, J. E. C. ; Raymond, C. A. ; Russell, C. T. (December 2017). "Exploring Tectonic Activity on Vesta and Ceres". American Geophysical Union, Fall Meeting 2017, abstract #P53G-02.
{{cite journal}}
: CS1 maint: multiple names: authors list (link) - ^ Schröder, Stefan E; Carsenty, Uri; Hauber, Ernst; Raymond, Carol; Russell, Christopher (May 2021). "The brittle boulders of dwarf planet Ceres". Planetary Science Journal.
- ^ "Catalog Page for PIA22660". photojournal.jpl.nasa.gov.
- ^ a b "PIA22660: Ceres' Internal Structure (Artist's Concept)". Photojournal. Jet Propulsion Laboratory. 14 August 2018. Retrieved 22 April 2019. This article incorporates text from this source, which is in the public domain.
- ^ M. Neveu and S. J. Desch (2016) 'Geochemistry, thermal evolution, and cryovolanism on Ceres with a muddy ice mantle'. 47th Lunar and Planetary Science Conference
- ^ "Confirmed: Ceres Has a Transient Atmosphere". Universe Today. 6 April 2017. Retrieved 14 April 2017.
- ^ a b c Küppers, M.; O'Rourke, L.; Bockelée-Morvan, D.; Zakharov, V.; Lee, S.; Von Allmen, P.; Carry, B.; Teyssier, D.; Marston, A.; Müller, T.; Crovisier, J.; Barucci, M. A.; Moreno, R. (23 January 2014). "Localized sources of water vapour on the dwarf planet (1) Ceres". Nature. 505 (7484): 525–527. Bibcode:2014Natur.505..525K. doi:10.1038/nature12918. ISSN 0028-0836. PMID 24451541. S2CID 4448395.
- ^ Campins, H.; Comfort, C. M. (23 January 2014). "Solar system: Evaporating asteroid". Nature. 505 (7484): 487–488. Bibcode:2014Natur.505..487C. doi:10.1038/505487a. PMID 24451536. S2CID 4396841.
- ^ Hansen, C. J.; Esposito, L.; Stewart, A. I.; Colwell, J.; Hendrix, A.; Pryor, W.; Shemansky, D.; West, R. (10 March 2006). "Enceladus' Water Vapor Plume". Science. 311 (5766): 1422–1425. Bibcode:2006Sci...311.1422H. doi:10.1126/science.1121254. PMID 16527971. S2CID 2954801.
- ^ Roth, L.; Saur, J.; Retherford, K. D.; Strobel, D. F.; Feldman, P. D.; McGrath, M. A.; Nimmo, F. (26 November 2013). "Transient Water Vapor at Europa's South Pole" (PDF). Science. 343 (6167): 171–174. Bibcode:2014Sci...343..171R. doi:10.1126/science.1247051. PMID 24336567. S2CID 27428538. Retrieved 26 January 2014.
- ^ O'Brien, D. P.; Travis, B. J.; Feldman, W. C.; Sykes, M. V.; Schenk, P. M.; Marchi, S.; Russell, C. T.; Raymond, C. A. (March 2015). "The Potential for Volcanism on Ceres due to Crustal Thickening and Pressurization of a Subsurface Ocean" (PDF). 46th Lunar and Planetary Science Conference. p. 2831. Retrieved 1 March 2015.
- ^ Jewitt, David; Hsieh, Henry; Agarwal, Jessica (2015). Michel, P.; et al. (eds.). The Active Asteroids (PDF). University of Arizona. pp. 221–241. arXiv:1502.02361. Bibcode:2015aste.book..221J. doi:10.2458/azu_uapress_9780816532131-ch012. ISBN 9780816532131. S2CID 119209764. Retrieved 30 January 2020.
{{cite book}}
:|journal=
ignored (help) - ^ Jewitt, D; Chizmadia, L.; Grimm, R.; Prialnik, D (2007). "Water in the Small Bodies of the Solar System" (PDF). In Reipurth, B.; Jewitt, D.; Keil, K. (eds.). Protostars and Planets V. University of Arizona Press. pp. 863–878. ISBN 978-0-8165-2654-3.
- ^ Hiesinger, H.; Marchi, S.; Schmedemann, N.; Schenk, P.; Pasckert, J. H.; Neesemann, A.; OBrien, D. P.; Kneissl, T.; Ermakov, A. I.; Fu, R. R.; Bland, M. T.; Nathues, A.; Platz, T.; Williams, D. A.; Jaumann, R.; Castillo-Rogez, J. C.; Ruesch, O.; Schmidt, B.; Park, R. S.; Preusker, F.; Buczkowski, D. L.; Russell, C. T.; Raymond, C. A. (1 September 2016). "Cratering on Ceres: Implications for its crust and evolution". Science. 353 (6303): aaf4759. Bibcode:2016Sci...353.4759H. doi:10.1126/science.aaf4759. PMID 27701089.
- ^ NASA/Jet Propulsion Laboratory (1 September 2016). "Ceres' geological activity, ice revealed in new research". ScienceDaily. Retrieved 8 March 2017.
- ^ Petit, Jean-Marc; Morbidelli, Alessandro (2001). "The Primordial Excitation and Clearing of the Asteroid Belt" (PDF). Icarus. 153 (2): 338–347. Bibcode:2001Icar..153..338P. doi:10.1006/icar.2001.6702. Retrieved 25 June 2009.
- ^ Greicius, Tony (29 June 2016). "Recent Hydrothermal Activity May Explain Ceres' Brightest Area". nasa.gov.
- ^ Nancy Atkinson (26 July 2016). "Large Impact Craters on Ceres Have Gone Missing". Universe Today. Retrieved 15 May 2021.
- ^ Wall, Mike (2 September 2016). "NASA's Dawn Mission Spies Ice Volcanoes on Ceres". Scientific American. Retrieved 8 March 2017.
- ^ Castillo-Rogez, J. C.; McCord, T. B.; Davis, A. G. (2007). "Ceres: evolution and present state" (PDF). Lunar and Planetary Science. XXXVIII: 2006–2007. Retrieved 25 June 2009.
- ^ Brandon Specktor (19 January 2021). "Humans could move to this floating asteroid belt colony in the next 15 years, astrophysicist says". livescience.com. Retrieved 23 June 2021.
- ^ Menzel, Donald H.; Pasachoff, Jay M. (1983). A Field Guide to the Stars and Planets (2nd ed.). Boston: Houghton Mifflin. p. 391. ISBN 978-0-395-34835-2.
- ^ Martinez, Patrick (1994). The Observer's Guide to Astronomy. Cambridge University Press. p. 298.
- ^ Millis, L. R.; Wasserman, L. H.; Franz, O. Z.; et al. (1987). "The size, shape, density, and albedo of Ceres from its occultation of BD+8°471". Icarus. 72 (3): 507–518. Bibcode:1987Icar...72..507M. doi:10.1016/0019-1035(87)90048-0. hdl:2060/19860021993.
- ^ "Keck Adaptive Optics Images the Dwarf Planet Ceres". Adaptive Optics. 11 October 2006. Archived from the original on 18 January 2010. Retrieved 27 April 2007.
- ^ a b Carry, Benoit; et al. (2007). "Near-Infrared Mapping and Physical Properties of the Dwarf-Planet Ceres" (PDF). Astronomy & Astrophysics. 478 (1): 235–244. arXiv:0711.1152. Bibcode:2008A&A...478..235C. doi:10.1051/0004-6361:20078166. S2CID 6723533. Archived from the original (PDF) on 30 May 2008.
- ^ "Largest Asteroid May Be 'Mini Planet' with Water Ice". HubbleSite. 7 September 2005. Retrieved 20 July 2021.
- ^ J.M. Houtkooper, D.Schulze-Makuch (2017). "Ceres: A Frontier in Astrobiology" (PDF). Astrobiology Science Conference (1965).
- ^ Ulivi, Paolo; Harland, David (2008). Robotic Exploration of the Solar System: Hiatus and Renewal, 1983–1996. Springer Praxis Books in Space Exploration. Springer. pp. 117–125. ISBN 978-0-387-78904-0.
- ^ Russell, C. T.; Capaccioni, F.; Coradini, A.; et al. (October 2007). "Dawn Mission to Vesta and Ceres" (PDF). Earth, Moon, and Planets. 101 (1–2): 65–91. Bibcode:2007EM&P..101...65R. doi:10.1007/s11038-007-9151-9. S2CID 46423305. Retrieved 13 June 2011.
- ^ Cook, Jia-Rui C.; Brown, Dwayne C. (11 May 2011). "NASA's Dawn Captures First Image of Nearing Asteroid". NASA/JPL. Retrieved 14 May 2011.
- ^ Schenk, P. (15 January 2015). "Year of the 'Dwarves': Ceres and Pluto Get Their Due". Planetary Society. Retrieved 10 February 2015.
- ^ a b Rayman, Marc (1 December 2014). "Dawn Journal: Looking Ahead at Ceres". Planetary Society. Retrieved 2 March 2015.
- ^ Rayman, Marc (6 March 2015). "Dawn Journal: Ceres Orbit Insertion!". The Planetary Society. Retrieved 6 March 2015.
- ^ Rayman, Marc (3 March 2014). "Dawn Journal: Maneuvering Around Ceres". Planetary Society. Retrieved 6 March 2015.
- ^ Rayman, Marc (30 April 2014). "Dawn Journal: Explaining Orbit Insertion". Planetary Society. Retrieved 6 March 2015.
- ^ Rayman, Marc (30 June 2014). "Dawn Journal: HAMO at Ceres". Planetary Society. Retrieved 6 March 2015.
- ^ Rayman, Marc (31 August 2014). "Dawn Journal: From HAMO to LAMO and Beyond". Planetary Society. Retrieved 6 March 2015.
- ^ Russel, C. T.; Capaccioni, F.; Coradini, A.; et al. (2006). "Dawn Discovery mission to Vesta and Ceres: Present status". Advances in Space Research. 38 (9): 2043–2048. arXiv:1509.05683. Bibcode:2006AdSpR..38.2043R. doi:10.1016/j.asr.2004.12.041.
- ^ Rayman, Marc (30 January 2015). "Dawn Journal: Closing in on Ceres". Planetary Society. Retrieved 2 March 2015.
- ^ "Dawn data from Ceres publicly released: Finally, color global portraits!". The Planetary Society. Retrieved 9 November 2015.
- ^ Plait, Phil (11 May 2015). "The Bright Spots of Ceres Spin Into View". Slate. Retrieved 30 May 2015.
{{cite journal}}
: Check|first=
value (help) - ^ O'Neill, Ian (25 February 2015). "Ceres' Mystery Bright Dots May Have Volcanic Origin". Discovery Inc. Retrieved 1 March 2015.
- ^ "LPSC 2015: First results from Dawn at Ceres: provisional place names and possible plumes". The Planetary Society.
- ^ "Ceres RC3 Animation". Jet Propulsion Laboratory. 11 May 2015. Retrieved 31 July 2015.
- ^ De Sanctis, M. C.; et al. (29 June 2016). "Bright carbonate deposits as evidence of aqueous alteration on (1) Ceres". Nature. 536 (7614): 54–57. Bibcode:2016Natur.536...54D. doi:10.1038/nature18290. PMID 27362221. S2CID 4465999.
- ^ Rayman, Marc (13 June 2018). "Dawn – Mission Status". Jet Propulsion Laboratory. Retrieved 16 June 2018.
- ^ Marc Rayman (2018). "Dear Dawntasmagorias". NASA Jet Propulsion Laboratory. Retrieved 21 July 2021.
- ^ "China's Deep-space Exploration to 2030 by Zou Yongliao Li Wei Ouyang Ziyuan Key Laboratory of Lunar and Deep Space Exploration, National Astronomical Observatories, Chinese Academy of Sciences, Beijing" (PDF).
External links
- Ceres Trek – An integrated map browser of datasets and maps for 1 Ceres
- Ceres 3D Model – NASA
- Destination Ceres:Breakfast at Dawn – NASA
- Dawn mission home page at JPL
- Simulation of the orbit of Ceres
- Google Ceres 3D, interactive map of the dwarf planet
- How Gauss determined the orbit of Ceres Archived 14 April 2008 at the Wayback Machine from keplersdiscovery.com
- Animated reprojected colorized map of Ceres (22 February 2015)
- Video (3:34): Ceres "Bright Spots" – Mystery solved (10 August 2020) on YouTube
- Rotating relief model of Ceres by Seán Doran (about 60% of a full rotation; starts with Occator midway above center)
- Ceres (dwarf planet) at AstDyS-2, Asteroids—Dynamic Site
- Ceres at the JPL Small-Body Database