Ceres (dwarf planet)

Ceres (IPA: [ˈsiɹiz], Latin: Cerēs), also designated 1 Ceres or (1) Ceres (See Minor Planet Names), is the smallest dwarf planet in the Solar System and the only one located in the main asteroid belt. Its name is derived from the Roman goddess Ceres — the goddess of growing plants and of motherly love. It was discovered on January 1 1801, by Giuseppe Piazzi. With a diameter of about 950 km, Ceres is by far the largest and most massive body in the asteroid belt, and contains approximately a third of the belt's total mass. Recent observations have revealed that it is spherical, unlike the irregular shapes of smaller asteroids with less gravity.

Contents

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Name

Piazzi's Book "Della scoperta del nuovo pianeta Cerere Ferdinandea" outlining the discovery of Ceres
Piazzi's Book "Della scoperta del nuovo pianeta Cerere Ferdinandea" outlining the discovery of Ceres

Piazzi originally suggested the name Ceres Ferdinandea (Ital­ian, Cerere Ferdinan­dea) for this body, after both the mythological figure Ceres (Roman goddess of plants) and King Ferdinand III of Sicily.[7] "Ferdinandea" was not acceptable to other nations of the world and was thus dropped. Ceres was also called Hera for a short time in Germany. In Greece, it is called Δήμητρα (Demeter), after the goddess Ceres' Greek equivalent; in English usage, Demeter is the name of a different asteroid (1108 Demeter).

Due to the rarity of the usage, there is no consensus as to the proper adjectival form of the name, although the nonce forms Cerian and Cerean have been used in fiction. Grammatically, the form Cererean would be correct (cf. its genitive, Cereris).

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Symbol

Ceres' astronomical symbol is a sickle, ʡ U+02A1 (Sickle variant symbol of Ceres), similar to Venus' symbol (Astronomical symbol of Venus) which is the female gender symbol and Venus' hand mirror. There have been several variants of the sickle design, including Old symbol of Ceres, Mirror variant symbol of Ceres and Other sickle variant symbol of Ceres.

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Discovery

Piazzi was searching for a star listed by Francis Wollaston as Mayer 87 because it was not in Mayer's zodiacal catalogue in the position given. Instead, Piazzi found a moving star-like object, which he thought at first was a comet.

Piazzi observed Ceres a total of 24 times, the final time on February 11, when illness interrupted. On January 24 1801, Piazzi announced his discovery in letters to fellow astronomers, among them his fellow countryman, Barnaba Oriani of Milan. 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".[8] In April, Piazzi sent his complete observations to Oriani, Bode, and Lalande in Paris. They were shortly thereafter published in the September, 1801 issue of the Monatliche Correspondenz.

To recover Ceres, Carl Friedrich Gauss, then only 24 years old, developed a method of orbit determination from three observations. In only a few weeks, he predicted its path, and sent his results to Franz Xaver, Baron von Zach, the editor of the Monatliche Correspondenz. On December 31 1801, von Zach and Heinrich W. M. Olbers unambiguously confirmed the recovery of Ceres.

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Status

Ceres (left) in comparison with the Moon (right).
Ceres (left) in comparison with the Moon (right).

The classification of Ceres has changed more than once. At the time of its discovery it was considered a planet; it was classified as an asteroid for over 150 years; and was first classified a dwarf planet in 2006.

Johann Elert Bode believed Ceres to be the "missing planet" that Johann Daniel Titius had proposed to exist between Mars and Jupiter, at a distance of 419 million km (2.8 AU) from the Sun. Ceres was assigned a planetary symbol, and remained listed as a planet in astronomy books and tables (along with 2 Pallas, 3 Juno and 4 Vesta) for about half a century until further asteroids were discovered. However as further objects were discovered in the area it was realised that it represented the first of a class of many similar bodies. Sir William Herschel coined in 1802 the term asteroid ("star-like") for such bodies[9], writing, "they resemble small stars so much as hardly to be distinguished from them, even by very good telescopes".[10] As the first such body to be discovered, it was given the designation 1 Ceres under the modern system of asteroid numbering.

The 2006 debate surrounding Pluto and what constitutes a 'planet' led to Ceres being considered for reclassification as a planet. An unsuccessful 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"[11][12]. Had this resolution been adopted, this would have made Ceres the fifth planet in order from the Sun.[13] This draft definition was not accepted, and in its place an alternate definition of "planet" came into effect as of August 24, 2006. Under this definition, a 'planet' is "a celestial body that is in orbit around the sun, has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a ... nearly round shape, and has cleared the neighborhood around its orbit." By this definition, Ceres (along with Pluto) cannot be classified as a planet, and both are now classified as "dwarf planets", although it remains unclear as to whether or not it is also classified as an asteroid.[14]

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Orbit

Ceres follows an orbit between Mars and Jupiter, within the main asteroid belt, with a period of 4.6 years. The orbit is moderately inclined (i=10.6° to be compared with 7° for Mercury and 17° for Pluto) and moderately eccentric (e=0.08 to compare with 0.09 for Mars).

The diagram illustrates the orbits of Ceres (blue) and several planets (white/grey). The segments of orbits below the ecliptic are plotted in darker colours, and the orange plus sign is the Sun's location. The top left diagram is a polar view that shows the location of Ceres in the gap between Mars and Jupiter. The top right is a close-up demonstrating the locations of the perihelia (q) and aphelia (Q) of Ceres and Mars. Interestingly, the perihelia of Ceres (as well as those of several other of the largest main belt asteroids) and Mars are on the opposite sides of the Sun. The bottom diagram is a perspective view showing the inclination of the orbit of Ceres compared to the orbits of Mars and Jupiter.

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Physical characteristics

Hubble Space Telescope images of Ceres, taken in 2003/4 with a resolution of about 30 km. The nature of the bright spot is uncertain. A movie was also made.
Hubble Space Telescope images of Ceres, taken in 2003/4 with a resolution of about 30 km. The nature of the bright spot is uncertain. A movie was also made.[15]
Hubble Space Telescope UV image of Ceres, taken in 1995 with a resolution of about 60 km. The "Piazzi" feature is the dark spot in the center.
Hubble Space Telescope UV image of Ceres, taken in 1995 with a resolution of about 60 km. The "Piazzi" feature is the dark spot in the center.

Ceres is the largest object in the asteroid belt, which mostly lies between Mars and Jupiter. However, it is not the largest object besides the Sun, planets and their satellites, in the solar system: the Kuiper belt is known to contain larger objects, including Eris, Pluto, 50000 Quaoar, 90482 Orcus, and 90377 Sedna.

At certain points in its orbit, Ceres can reach a magnitude of 7.0. This is generally regarded as being just barely too dim to be seen with the naked eye, but under exceptional viewing conditions a very sharp-sighted person may be able to see the asteroid with the naked eye. The only other asteroid that can be seen with the naked eye is 4 Vesta.

Ceres' size and mass are sufficient to give it a nearly spherical shape. That is, it is close to hydrostatic equilibrium. Other large asteroids such as 2 Pallas, 3 Juno, and 4 Vesta are known to be quite irregular, while lightcurve analysis of 10 Hygiea indicates it is oblong although it appears spheroidal in low-resolution images (presumably due to viewing angle).

With a mass of 9.5 ×1020 kg, Ceres comprises about a third of the estimated total 3.0 ± 0.2 ×1021 kg mass of all the asteroids in the solar system[16] (note how all these amount to only about 4% of the mass of the Moon).

There are some indications that the surface of Ceres is relatively warm and that it may have a tenuous atmosphere and frost. The maximum temperature with the Sun overhead was estimated from measurements to be 235 K (about -38°C) on May 5 1991.[6] Taking into account also the heliocentric distance at the time, this gives an estimated maximum of ~239 K at perihelion.

Diagram showing differentiated layers of Ceres
Diagram showing differentiated layers of Ceres

A study led by Peter Thomas of Cornell University suggests that Ceres has a differentiated interior: observations coupled with computer models suggest the presence of a rocky core overlain with an icy mantle. This mantle of thickness from 120 to 60 km could contain 200 million cubic kilometres of water, which is more than the amount of fresh water on the Earth.[17][2]

There has been some ambiguity regarding surface features on Ceres. Low resolution ultraviolet Hubble Space Telescope images taken in 1995 showed a dark spot on its surface which was nicknamed "Piazzi" in honour of the discoverer of Ceres. This was thought to be a crater. Later images with a higher resolution taken over a whole rotation with the Keck telescope using adaptive optics showed no sign of "Piazzi". However, two dark features were seen to move with the asteroid's rotation, one with a bright central region. These are presumably craters. More recent visible light Hubble Space Telescope images of a full rotation taken in 2003 and 2004 show an enigmatic white spot, the nature of which is currently unknown.[18] The dark albedo features seen with Keck are, however, not immediately recognizable in these images.

These last observations also determined that Ceres' north pole points (give or take about 5°) in the direction of right ascension 19 h 24 min, declination +59°, in the constellation Draco. This means that Ceres' axial tilt is very small (about 4±5°).[2]

Ceres was long thought to be the parent body of the "Ceres asteroid family". However, that grouping is now defunct because Ceres has been shown to be an interloper in its "own" family, and physically unrelated. The bulk of that asteroid group is now called the Gefion family.

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Observations

Some notable observation milestones for Ceres include:

An occultation of a star by Ceres was observed in Mexico, Florida and across the Caribbean on November 13 1984.

Features on Ceres' surface have been telescopically imaged several times in recent years.

These include:

Radio signals from spacecraft in orbit around Mars and on its surface have been used to estimate the mass of Ceres from the perturbations induced by it onto the motion of Mars.[16]

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Exploration of Ceres

Artist's conception of Dawn visiting Ceres and Vesta.
Artist's conception of Dawn visiting Ceres and Vesta.

To date no space probes have visited Ceres. However, NASA is currently developing the Dawn Mission, with a projected launch in 2007. According to the current mission profile, Dawn is expected to explore the asteroid 4 Vesta in 2011 before arriving at Ceres in 2015.

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Namesakes

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Aspects

Stationary,
retrograde
Opposition Distance to
Earth (AU)
Maximum
brightness (mag)
Stationary,
prograde
Conjunction
to Sun
Mar 21 2005 May 8 2005 1.68631 7.0 Jun 30 2005 Dec 28 2005
Jun 26 2006 Aug 12 2006 1.98278 7.6 Nov 27 2006 Mar 22 2007
Sep 20 2007 Nov 9 2007 1.83690 7.2 Jan 1 2008 Jun 28 2008
Jan 17 2009 Feb 24 2009 1.58526 6.9 Apr 16 2009 Oct 31 2009
Apr 28 2010 Jun 18 2010 1.81988 7.0 Aug 9 2010 Jan 30 2011
Jul 31 2011 Sep 16 2011 1.99211 7.7 Nov 12 2011 Apr 26 2012
Oct 30 2012 Dec 17 2012 1.68842 6.7 Feb 4 2013 Aug 17 2013
Mar 1 2014 Apr 15 2014 1.63294 7.0 Jun 7 2014 Dec 10 2014
Jun 6 2015 Jul 25 2015 1.94252 7.5 Sep 16 2015 Mar 3 2016
Sep 1 2016 Oct 20 2016 1.90844 7.4 Dec 15 2016 Jun 5 2017
Dec 21 2017 Jan 31 2018 1.59531 8.8 Mar 20 2018 Oct 7 2018
Apr 9 2019 May 29 2019 1.74756 7.0 Jul 20 2019 Jan 14 2020
Jul 13 2020 Aug 28 2020 1.99916 7.7 Oct 23 2020 Apr 7 2021
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See also

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References

  1. Ted Bowell, Bruce v (January 2, 2003). Asteroid Observing Services. Lowell Observatory. Retrieved on 2007-01-17.
  2. 2.0 2.1 2.2 2.3 P. C. Thomas et al Differentiation of the asteroid Ceres as revealed by its shape, Nature, Vol. 437, pp. 224 (2005).
  3. E.V. Pitjeva (2005). "High-Precision Ephemerides of Planets—EPM and Determination of Some Astronomical Constants". Solar System Research 39: 176.
  4. D. T. Britt et al Asteroid density, porosity, and structure, pp. 488 in Asteroids III, University of Arizona Press (2002).
  5. Supplemental IRAS Minor Planet Survey.
  6. 6.0 6.1 6.2 O. Saint-Pé Ceres surface properties by high-resolution imaging from earth, Icarus, vol. 105 pp. 271 (1993).
  7. Hoskin, Michael. Bodes' Law and the Discovery of Ceres. Osservatorio Astronomico Di Palermo Giuseppe S. Vaiana. Retrieved on 2007-01-17.
  8. Hoskin, Michael. 8. Piazzi and the Discovery of Ceres. Bode's Law and the Disovery of Ceres. Osservatorio Astronomico di Palermo, Giuseppe S. Vaiana. Retrieved on 2006-08-16.
  9. Hilton, Dr. J. L. (September 17 2001). When Did the Asteroids Become Minor Planets?. Retrieved on 2006-08-16.
  10. Herschel, William (May 6 1802). Observations on the two lately discovered celestial Bodies..
  11. http://www.iau2006.org/mirror/www.iau.org/iau0601/iau0601_release.html
  12. http://www.latimes.com/news/science/la-sci-planets16aug16,0,3652893.story?coll=la-home-headlines?invade Proposal would increase from 9 to 12
  13. http://www.spacedaily.com/reports/The_IAU_Draft_Definition_Of_Planets_And_Plutons_999.html
  14. http://www.iau2006.org/mirror/www.iau.org/iau0603/iau0603_Q_A2.html "Ceres was an asteroid" - but note it then talks about "other asteroids" crossing Ceres' path.
  15. Cooke, Bill. "An icy interior for Ceres?", Astronomy, September 12 2005. movie credit J. Parker, Southwest Research Institute
  16. 16.0 16.1 E. V. Pitjeva High-Precision Ephemerides of Planets — EPM and Determination of Some Astronomical Constants, Solar System Resarch, Vol. 39 pp. 176 (2005).
  17. "Largest Asteroid Might Contain More Fresh Water than Earth", SPACE.com, 07 September 2005. Retrieved on 2006-08-16.
  18. 18.0 18.1 "Largest Asteroid May Be 'Mini Planet' with Water Ice", HubbleSite, September 7 2005. Retrieved on 2006-08-16.
  19. Observations reveal curiosities on the surface of asteroid Ceres. Retrieved on 2006-08-16.
  20. J. W. Parker et al Analysis of the first disk-resolved images of Ceres from ultraviolet observations with the Hubble Space Telescope, The Astronomical Journal, Vol. 123 pp. 549 (2002).
  21. http://s1.simpload.com/10034341d7edcf588.jpg
  22. Keck Adaptive Optics Images the Dwarf Planet Ceres
  23. Cerium Historical Information. Retrieved on 2006-08-21.
  24. Amalgamator Features 2003: 200 Years Ago. Retrieved on 2006-08-21.
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External links

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