Ceres
Ceres information Average distance from Sun: 413715000 km (2.7655 AU) Perihelion (closest): 380612000 km Perihelion (farthest): 446818000 km Equatorial radius: 975 × 909 km (Diameter: 1950 km) Mass: 95000000 kg Density: 2.08 g/cm³ Equatorial surface gravity: 0.27 m/s² Escape velocity: 510 m/s Siderial rotation period (length of day): 9.07 earth hours Siderial orbit period (length of year): 1679.819 earth days Mean orbit velocity: 17882 m/s Orbital eccentricity: 0.080 Orbital inclination to ecliptic: 10.587 degrees Equatorial inclination to orbit: 108.509 degrees Surface temperature (min/max): 167/239 K		Ceres, Sun
Ceres Ceres (seer'-eez (key), IPA /?si?riz/, Latin: Cere-s) was the first asteroid to be discovered. Its name is derived from the Roman goddess Ceres; it is prefixed by the number 1, which is its number under the modern system of asteroid numbering. 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 asteroid in the asteroid belt: it contains approximately a third of the belt's total mass. It was originally classified as a planet upon its discovery, but has since been reclassified as an asteroid, and remained so for over 150 years. It may, however, soon be reclassified as a planet and known informally as a 'Dwarf planet' if a new proposal under consideration by the International Astronomical Union is passed. This draft definition of 'planet' will be voted on by the IAU on August 24, 2006. Ceres was originally named Ceres Ferdinandea after both the mythological figure Ceres (Roman goddess of plants and motherly love) and King Ferdinand III of Sicily (also known as Ferdinand IV of Naples, and as Ferdinand I of the Two Sicilies). King Ferdinand was taking refuge in Palermo at the time, the Kingdom of Naples having been conquered by the French in 1798. The 'Ferdinandea' part was not acceptable to other nations of the world and was dropped. Ceres was also called Hera for a short time in Germany. The regular adjectival form of the name would be Cererian (or Cererine), although the nonce forms Cerian and Cerean have been used in fiction. Ceres was discovered by accident. 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 (it eventually transpired that Wollaston had made a mistake -the star was in fact Lacaille 87). 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'. By early February Ceres was lost as it receded behind the Sun. 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 the asteroid, Carl Friedrich Gauss, then only 24 years old, developed a method of orbit determination from three observations. In only a few weeks, he predicted the path of Ceres, 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. Johann Elert Bode believed Ceres to be the 'missing planet' that Johann Daniel Titius had calculated 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, Ceres turned out to be disappointingly small, showing no discernible disc, and so Sir William Herschel coined the term 'asteroid' ('star-like') to describe it. Recent debate surrounding Pluto and what constitutes a 'planet' may lead to Ceres being reinstated as a planet. A proposal before the International Astronomical Union for the definition of a planet defines 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'. If this resolution is adopted, this would make Ceres the fifth planet in order from the Sun. Ceres follows an orbit between Mars and Jupiter, within the main asteroid belt, completing it in 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). Ceres is the largest known asteroid in the asteroid belt, which mostly lies between Mars and Jupiter. However, it is not the largest object besides planets in the solar system: the Kuiper belt is known to contain larger objects, including 50000 Quaoar, 90482 Orcus, 2003 UB313, and possibly 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 is rare among asteroids in that its size and mass are sufficient to give it a nearly spherical shape: That is, it is a gravitationally relaxed equilibrium spheroid, or 'planetary body'. The only other known gravitationally relaxed asteroid is 4 Vesta. Other large asteroids such as 2 Pallas and 3 Juno are known to be distinctly non-spherical, while lightcurve analysis of 10 Hygiea indicates it is oblong although it appeared spheroidal in low-resolution images (presumably due to viewing angle). If the proposed Resolution 5 of the 2006 Meeting of the International Astronomical Union is approved (on 24 August 2006), Ceres's gravitationally relaxed equilibrium would allow it to qualify as a planet. 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 (note how all these amount to only about 4% of the mass of the Moon). There are some indications that the Cererian surface 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. Taking into account also the heliocentric distance at the time, gives an estimated maximum of ~239 K at perihelion. A more recent 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. 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. 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. 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: Ultraviolet Hubble Space Telescope images with 50 km resolution taken in 1995. Visible images with 60 km resolution taken with the Keck telescope in 2002 using adaptive optics. The best resolution to date (30 km) visible light images using Hubble again in 2003 and 2004. Radar signals from spacecraft in orbit around Mars and on its surface have been used to estimate the mass of Ceres from the tiny perturbations induced by it onto the motion of Mars. To date no space probes have visited Ceres. However, NASA's Dawn mission will be the first spacecraft to study Ceres. Initially the probe will visit the second most massive asteroid, 4 Vesta, for approximately six months in 2010, before arriving at Ceres in 2014 or 2015.
More Discovered by Giuseppe Piazzi in January 1, 1801
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