Ceres (dwarf planet)

Ceres ⚳
Ceres - RC3 - Haulani Crater (22381131691) (cropped).jpg
A view of Ceres in natural color, pictured by the Dawn spacecraft in May 2015. [a]
Discovery [1]
Discovered by Giuseppe Piazzi
Discovery date 1 January 1801
Designations
MPC designation 1 Ceres
Pronunciation z/
Named after
Cerēs
A899 OF; 1943 XB
Dwarf planet
Asteroid belt
Adjectives Cererian n/,
rarely Cererean n/ [2]
Orbital characteristics [4]
Epoch 2014-Dec-09
( JD 2,457,000.5)
Aphelion 2.9773  AU
(445,410,000 km)
Perihelion 2.5577 AU
(382,620,000 km)
2.7675 AU
(414,010,000 km)
Eccentricity 0.075823
4.60  yr
1,681.63 d
466.6  d
1.278  yr
17.905 km/s
95.9891°
Inclination 10.593° to ecliptic
9.20° to invariable plane [3]
80.3293°
72.5220°
Satellites None
Proper orbital elements [5]
2.7670962  AU
0.1161977
9.6474122°
78.193318  deg / yr
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 (965.2 × 961.2
× 891.2) ± 2.0 km [6]
Mean radius
473 km [6]
2,770,000 km2 [7]
Volume 421,000,000 km3 [7]
Mass

(9.393±0.005)×1020 kg [6]

0.00015  Earths
0.0128 Moons
Mean density
2.161±0.009 g/cm3 [8]
0.28 m/s2 [7]
0.029 g
0.37 [9] [b] (estimate)
0.51 km/s [7]
0.3781 d
9.074170±0.000002 h [10]
Equatorial rotation velocity
92.61 m/s [7]
[11]
North pole right ascension
291.42744° [12]
North pole declination
66.764° [11]
Albedo 0.090±0.0033 ( V-band geometric) [13]
Surface temp. min mean max
Kelvin ? ≈ 168 K [17] 235 K [18]
Spectral type
C [14]
6.64 [15] to 9.34 [16]
3.36±0.02 [13]
0.854″ to 0.339″

Ceres ( z/; [19] minor-planet designation: 1 Ceres) is the largest object in the asteroid belt that lies between the orbits of Mars and Jupiter. Its diameter is approximately 945 kilometers (587 miles), [6] making it the largest of the minor planets within the orbit of Neptune. The 33rd- largest known body in the Solar System, it is the only dwarf planet within the orbit of Neptune. [c] [20] Composed of rock and ice, Ceres is estimated to compose approximately one third of the mass of the entire asteroid belt. Ceres is the only object in the asteroid belt known to be rounded by its own gravity (though detailed analysis was required to exclude 4 Vesta). From Earth, the apparent magnitude of Ceres ranges from 6.7 to 9.3, and hence even at its brightest it is too dim to be seen with the naked eye except under extremely dark skies.

Ceres was the first asteroid to be discovered (by Giuseppe Piazzi at Palermo on 1 January 1801). It was originally considered a planet, but was reclassified as an asteroid in the 1850s after many other objects in similar orbits were discovered.

Ceres appears to be differentiated into a rocky core and an icy mantle, and may have a remnant internal ocean of liquid water under the layer of ice. [21] [22] The surface is probably a mixture of water ice and various hydrated minerals such as carbonates and clay. In January 2014, emissions of water vapor were detected from several regions of Ceres. [23] This was unexpected because large bodies in the asteroid belt typically do not emit vapor, a hallmark of comets.

The robotic NASA spacecraft Dawn entered orbit around Ceres on 6 March 2015. [24] [25] [26] 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 [27]) were seen in a 19 February 2015 image, leading to speculation about a possible cryovolcanic origin [28] [29] [30] or outgassing. [31] On 3 March 2015, a NASA spokesperson said the spots are consistent with highly reflective materials containing ice or salts, but that cryovolcanism is unlikely. [32] However, on 2 September 2016, NASA scientists released a paper in Science that claimed that a massive ice volcano called Ahuna Mons is the strongest evidence yet for the existence of these mysterious ice volcanoes. [33] [34] On 11 May 2015, NASA released a higher-resolution image showing that, instead of one or two spots, there are actually several. [35] 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. [36] In June 2016, near-infrared spectra of these bright areas were found to be consistent with a large amount of sodium carbonate (Na
2
CO
3
), implying that recent geologic activity was probably involved in the creation of the bright spots. [37] [38] [39]

In October 2015, NASA released a true color portrait of Ceres made by Dawn. [40] In February 2017, organics were reported to have been detected on Ceres in Ernutet crater ( see image). [41]

History

Discovery

Piazzi's book Della scoperta del nuovo pianeta Cerere Ferdinandea outlining the discovery of Ceres, dedicated the new "planet" to Ferdinand I of the Two Sicilies.

Johann Elert Bode, in 1772, first suggested that an undiscovered planet could exist between the orbits of Mars and Jupiter. [42] Kepler had already noticed the gap between Mars and Jupiter in 1596. [42] Bode based his idea on the Titius–Bode law which is a now-discredited hypothesis that was first proposed in 1766. Bode observed that there was a regular pattern in the semi-major axes of the orbits of known planets, and that the pattern was marred only by the large gap between Mars and Jupiter. [42] [43] The pattern predicted that the missing planet ought to have an orbit with a semi-major axis near 2.8 astronomical units (AU). [43] William Herschel's discovery of Uranus in 1781 [42] near the predicted distance for the next body beyond Saturn increased faith in the law of Titius and Bode, and in 1800, a group headed by Franz Xaver von Zach, editor of the Monatliche Correspondenz, sent requests to twenty-four experienced astronomers (whom he dubbed the "celestial police"), asking that they combine their efforts and begin a methodical search for the expected planet. [42] [43] Although they did not discover Ceres, they later found several large asteroids. [43]

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. [44] [45] He was searching for "the 87th [star] of the Catalogue of the Zodiacal stars of Mr la Caille", but found that "it was preceded by another". [42] Instead of a star, Piazzi had found a moving star-like object, which he first thought was a comet. [46] 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 of Berlin. [47] 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". [42] In April, Piazzi sent his complete observations to Oriani, Bode, and Jérôme Lalande in Paris. The information was published in the September 1801 issue of the Monatliche Correspondenz. [46]

By this time, the apparent position of Ceres had changed (mostly due to Earth's orbital motion), and was too close to the Sun's glare for other astronomers to confirm Piazzi's observations. Toward the end of the year, Ceres should have been visible again, but after such a long time it was difficult to predict its exact position. To recover Ceres, Carl Friedrich Gauss, then 24 years old, developed an efficient method of orbit determination. [46] In only a few weeks, he predicted the path of Ceres and sent his results to von Zach. On 31 December 1801, von Zach and Heinrich W. M. Olbers found Ceres near the predicted position and thus recovered it. [46]

The early observers were only able to calculate the size of Ceres to within an order of magnitude. Herschel underestimated its diameter as 260 km in 1802, whereas in 1811 Johann Hieronymus Schröter overestimated it as 2,613 km. [48] [49]

Name

Piazzi originally suggested the name Cerere Ferdinandea for his discovery, after the goddess Ceres ( Roman goddess of agriculture, Cerere in Italian, who was believed to have originated in Sicily and whose oldest temple was there) and King Ferdinand of Sicily. [42] [46] "Ferdinandea", however, was not acceptable to other nations and was dropped. Ceres was called Hera for a short time in Germany. [50] In Greece, it is called Demeter (Δήμητρα), after the Greek equivalent of the Roman Cerēs; [d] in English, that name is used for the asteroid 1108 Demeter.

The regular adjectival forms of the name are Cererian and Cererean, [51] derived from the Latin genitive Cereris, [2] but Ceresian is occasionally seen for the goddess (as in the sickle-shaped Ceresian Lake), as is the shorter form Cerean.

The old astronomical symbol of Ceres is a sickle, ⟨⚳⟩ ( Sickle variant symbol of Ceres), [52] similar to Venus' symbol ⟨⟩ but with a break in the circle. It has a variant ⟨ Cee variant symbol of Ceres ⟩, reversed under the influence of the initial letter 'C' of 'Ceres'. These were later replaced with the generic asteroid symbol of a numbered disk, ⟨①⟩. [46] [53]

Cerium, a rare-earth element discovered in 1803, was named after Ceres. [54] [e] In the same year another element was also initially named after Ceres, but when cerium was named, its discoverer changed the name to palladium, after the second asteroid, 2 Pallas. [56]

Classification

The categorization of Ceres has changed more than once and has been the subject of some disagreement. Johann Elert Bode believed Ceres to be the "missing planet" he had proposed to exist between Mars and Jupiter, at a distance of 419 million km (2.8 AU) from the Sun. [42] Ceres was assigned a planetary symbol, and remained listed as a planet in astronomy books and tables (along with 2 Pallas, 3 Juno, and 4 Vesta) for half a century. [42] [46] [57]

Sizes of the first ten main-belt objects discovered profiled against the Moon. Ceres is far left (1).

As other objects were discovered in the neighborhood of Ceres, it was realized that Ceres represented the first of a new class of objects. [42] In 1802, with the discovery of 2 Pallas, William Herschel coined the term asteroid ("star-like") for these bodies, [57] writing that "they resemble small stars so much as hardly to be distinguished from them, even by very good telescopes". [58] As the first such body to be discovered, Ceres was given the designation 1 Ceres under the modern system of minor-planet designations. By the 1860s, the existence of a fundamental difference between asteroids such as Ceres and the major planets was widely accepted, though a precise definition of "planet" was never formulated. [57]

Ceres (bottom left), the Moon and Earth, shown to scale
Ceres (bottom left), the Moon and Earth, shown to scale
Size comparison of Vesta, Ceres and Eros
Size comparison of Vesta, Ceres and Eros

The 2006 debate surrounding Pluto and what constitutes a planet led to Ceres being considered for reclassification as a planet. [59] [60] A proposal before the International Astronomical Union for the definition of a planet would have defined a planet as "a celestial body that (a) has sufficient mass for its self-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". [61] Had this resolution been adopted, it would have made Ceres the fifth planet in order from the Sun. [62] This never happened, however, and on 24 August 2006 a modified definition was adopted, carrying 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 a third of the mass of the belt. Bodies that met the first proposed definition but not the second, such as Ceres, were instead classified as dwarf planets.

Ceres is the largest object in the asteroid belt. [14] It is sometimes assumed that Ceres has been reclassified as a dwarf planet, and that it is therefore no longer considered an asteroid. For example, a news update at Space.com spoke of "Pallas, the largest asteroid, and Ceres, the dwarf planet formerly classified as an asteroid", [63] whereas an IAU question-and-answer posting states, "Ceres is (or now we can say it was) the largest asteroid", though it then speaks of "other asteroids" crossing Ceres' path and otherwise implies that Ceres is still considered an asteroid. [64] The Minor Planet Center notes that such bodies may have dual designations. [65] The 2006 IAU decision that classified Ceres as a dwarf planet never addressed whether it is or is not an asteroid. Indeed, the IAU has never defined the word 'asteroid' at all, having preferred the term ' minor planet' until 2006, and preferring the terms ' small Solar System body' and 'dwarf planet' after 2006. Lang (2011) comments "the [IAU has] added a new designation to Ceres, classifying it as a dwarf planet. ... By [its] definition, Eris, Haumea, Makemake and Pluto, as well as the largest asteroid, 1 Ceres, are all dwarf planets", and describes it elsewhere as "the dwarf planet–asteroid 1 Ceres". [66] NASA continues to refer to Ceres as an asteroid, [67] as do various academic textbooks. [68] [69]

Other Languages
Alemannisch: (1) Ceres
Ænglisc: 1 Ceres
অসমীয়া: চেৰেছ
asturianu: 1 Ceres
Avañe'ẽ: Seres
বাংলা: সেরেস
беларуская (тарашкевіца)‎: Цэрэра (карлікавая плянэта)
Deutsch: (1) Ceres
Diné bizaad: Séwes
emiliàn e rumagnòl: Ceres
Esperanto: Cereso
فارسی: سرس
français: (1) Cérès
Հայերեն: Սերես
Ido: Ceres
Bahasa Indonesia: Ceres
Basa Jawa: Ceres
ქართული: ცერერა
kaszëbsczi: Ceres
қазақша: Церера
Kiswahili: 1 Ceres
коми: Церера
Kurdî: 1 Ceres
Кыргызча: Церера
latviešu: Cerera
Lëtzebuergesch: (1) Ceres
മലയാളം: സിറസ്
Bahasa Melayu: Ceres (planet kerdil)
монгол: Церера
Nāhuatl: Ceres
Napulitano: Cerere
norsk nynorsk: Dvergplaneten Ceres
oʻzbekcha/ўзбекча: Serera
پنجابی: سیرس
Plattdüütsch: Ceres (Dwargplanet)
polski: (1) Ceres
русский: Церера
shqip: Ceres
sicilianu: Cèriri
Simple English: Ceres (dwarf planet)
slovenčina: 1 Ceres
Soomaaliga: Ceres
کوردی: سێریس
srpskohrvatski / српскохрватски: 1 Ceres
Basa Sunda: 1 Ceres
suomi: Ceres
ไทย: ซีรีส
тоҷикӣ: Серера
ئۇيغۇرچە / Uyghurche: سېرېرا
Tiếng Việt: Ceres (hành tinh lùn)
文言: 穀神星
吴语: 穀神星
ייִדיש: צערעס
粵語: 穀神星
中文: 穀神星