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1 Ceres (, Latin Cerēs) was the first asteroid to be discovered. It was discovered on January 1, 1801, by Giuseppe Piazzi. With a diameter of about 950 km it is by far the largest and most massive asteroid in the asteroid belt: It contains 40% of the belt's total mass.

Name

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 (a.k.a. Ferdinand IV of Naples, a.k.a 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.

Discovery

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 24 January 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.

Physical characteristics

Ceres is the largest known asteroid in the asteroid belt, which mostly lies between Mars and Jupiter. However the Kuiper belt is known to contain larger objects, including Pluto, 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, although 10 Hygiea appears to be spheroidal in low-resolution images. Other large asteroids such as 2 Pallas and 3 Juno are known to be distinctly non-spherical.

With a mass of 9.5 × 10 kg, Ceres comprises about 40% of the estimated total 2.3 × 10 kg mass of all the asteroids in the solar system (which still only amounts to about 3% 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 kilometers 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. 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°) .

• 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.

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:

• 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 . Link to images here.
• 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 .

Exploration of Ceres

To date no space probes have visited Ceres. However, NASA's Dawn mission will be the first spacecraft to study Ceres. The probe will first visit the second larget asteroid, Vesta for approximately six months in 2010, before arriving at Ceres in 2014 or 2015.

Namesakes

• The chemical element Cerium (atomic number 58) was discovered in 1803 by Berzelius and Klaproth, working independently. Berzelius named the element after the asteroid.
• William Hyde Wollaston discovered palladium as early as 1802 and at first called it Ceresium. By the time he openly published his discovery in 1805, the name was already taken (by Berzelius) and he switched it to palladium in honour of 2 Pallas.

Ceres in fiction

• In Joe Haldeman's novel The Long Habit of Living (1989; British title; the U.S. title is Buying Time), Ceres is the home of a stateless society, which becomes important because of a secret research project to reinvent the Stileman rejuvenation process.
• In the PC role-playing game Countdown to Doomsday (1990), Ceres is the location of an abandoned RAM (enemy) research base.
• In the PC game Star Control II (1992), the destruction of Ceres Station by the invading Ur-Quan fleet signifies the defeat of the human race, leading to their subsequent enslavement.
• In the Super Nintendo game Super Metroid (1994), the Ceres Space Colony is where Samus Aran takes the last surviving Metroid hatchling from SR-388.
• In the movie The American Astronaut (2001) Ceres has a bar and a dance contest is held.

Aspects

External links

• Movie of one Cererian rotation (processed Hubble images)
• Ceres "Asteroids" games for Sony PSP (PlayStation Portable)

References

1. astronomy.com, movie credit J. Parker, Southwest Research Institute.
2. E. V. Pitjeva, Estimations of Masses of the Largest Asteroids and the Main Asteroid Belt From Ranging to Planets, Mars Orbiters And Landers Solar System Resarch, Vol. 39 pp. 176 (2005).
3. Supplemental IRAS Minor Planet Survey
4. Osservatorio Astronomico di Palermo, Giuseppe S. Vaiana
5. detailed essay by J. L. Hilton
6. Largest Asteroid Might Contain More Fresh Water than Earth September 7, 2005 Space.com
7. Hubble Space Telescope news archive .
8. http://www.swri.org/press/ceres.htm
9. http://s1.simpload.com/10034341d7edcf588.jpg
10. P. C. Thomas et al Differentiation of the asteroid Ceres as revealed by its shape, Nature, Vol. 437, pp. 224 (2005).
11. D. T. Britt et al Asteroid density, porosity, and structure, pp. 488 in Asteroids III, University of Arizona Press (2002).
12. O. Saint-Pé Ceres surface properties by high-resolution imaging from earth, Icarus, vol. 105 pp. 271 (1993).
13. 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).

• • Giuseppe Piazzi, Risultati delle Osservazioni della Nuova Stella, Palermo, 1801.
  • James L. Hilton, U.S. Naval Observatory Ephemerides of the Largest Asteroids The Astronomical Journal, Vol. 117 pp. 1077 (1999).

• Main Belt asteroids
• Asteroids named from Roman mythology
• G-type asteroids
• Solar System bodies formerly considered planets