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{{Infobox Planet|image=Ceres.jpg
'''Ceres''' is the largest planetoid in the [[Asteroid Belt]], roughly one-fourth of the diameter of the [[Moon]]. Astronomers recently upgraded Ceres from [[asteroid]] to the new class of bodies called [[dwarf planet|dwarf planets]]. [[NASA]] plans to explore Ceres with a probe in 2015. <ref>http://news.bbc.co.uk/2/hi/science/nature/6037844.stm</ref>
|discname=Giuseppe Piazzi
|origname=Roman goddess of agriculture
|primary=Sun
|order=5
|periapsis=2.545 AU
|apoapsis=2.987 AU
|semimajor=2.765956424 AU
|bode=2.8 AU
|eccentricity=0.07976017
|sidereal=4.599 a
|orbitspeed=17.882 km/s
|inclination=10.586712°
|reference=the ecliptic
|siderealday=9.074 h (0.378 da)
|axialtilt=3°
|mass=9.46 * 10<sup>20</sup> kg (0.0158% earth)
|density=2,077 kg/m³
|surfacegrav=0.27 m/s² (0.0275 ''g'')
|escapespeed= 0.51 km/s
|equatorradius=487.3 km
|polarradius=454.7 km
|surfacearea= 21,237,000 km² (4.164% earth)
|meantemp=167 K
|maxtemp=239 K
|moons=none known
}}'''Ceres''' is the largest planetoid and the first identified object in the [[Asteroid Belt]], roughly one-fourth of the diameter of the [[Moon]]. Giuseppe Piazzi discovered it on January 1, 1801. Recently, in the wake of the [[Eris]]-[[Pluto]] controversy, the [[International Astronomical Union]] has declared that it is more than a mere asteroid and qualifies as a [[dwarf planet]].
Ceres is named for the Roman goddess of agriculture, from which name the word ''cereal'' derives.
== Discovery ==
Piazzi was searching for the "missing planet" that, according to [[Bode's law]], should exist between [[Mars]] and [[Jupiter]]. Bode's law predicted an object having a semi-major axis of 2.8 AU, remarkably close to the actual semi-major axis of Ceres.
When Piazzi first observed Ceres, he thought he was looking at a [[comet]]. But comets normally move much faster than Ceres does, a fact Piazzi appreciated. He observed Ceres 24 times and reported his discoveries to Bode and other astronomers.
Shortly after the publication of Piazzi's findings, Ceres was lost in the glare of the sun. Karl Friedrich Gauss, then 24 years old, predicted Ceres' path and suggested where to look to reacquire Ceres. On December 31, 1801, the astronomer Baron von Zach found Ceres very near where Gauss said he might.
== Status ==
For many years Ceres was listed as a planet, even after the [[asteroid]]s [[Pallas]], [[Juno]], and [[Vesta]] were discovered. With the discovery of yet more objects in what would later be known as the Asteroid Belt, Ceres was reclassified as an asteroid, the largest of all such bodies. But Ceres, unlike any other object in the asteroid belt, has a hydrostatic-equilibrium shape, characteristic of an object sufficiently massive that its self-gravity forces such a shape despite the rigid-body forces that normally hold a solid object's shape.
In 2006, the discovery of [[Eris]] provoked a fresh look at all the bodies of the [[solar system]], and in particular what constituted a planet and what didn't. As a result of the debate, Eris and [[Pluto]], an object even smaller than Eris, were classed as [[dwarf planet]]s--a new classification with definite criteria. Ceres meets these criteria, and thus Ceres is considered a dwarf planet--the smallest of three known bodies of that class.
== Composition ==
Recent observations made by the Hubble Space Telescope suggest that Ceres might be very rich in [[water]] ice. Specifically, astronomers have concluded that Ceres has a layered interior, with a rocky inner core, a thick layer of water ice, and a dusty outer crust. McFadden specifically says that Ceres is an "embryonic planet," one that (according to evolutionary theory) tried to form a planet but could not because [[Jupiter]], being so close, so perturbed the local gravitational field that Ceres could not grow any larger than it is. Findings supporting the water-ice theory include:
# Most objects having hydrostatic-equilibrium or round shape have differentiated, or layered, interiors.
# Spectrography of the surface shows evidence of water-bearing minerals.
Parker and his colleagues speculate that Ceres might be composed of 25% water and thus have more fresh water than in all the fresh-water sources on [[earth]].
== Satellites ==
Ceres has no known satellites at present.
== Further exploration ==
[[NASA]] plans to explore Ceres with a probe in 2015. <ref>http://news.bbc.co.uk/2/hi/science/nature/6037844.stm</ref>
== References ==
== References ==
<references/>
<references/>
* Hamilton, Calvin J. "[http://www.solarviews.com/eng/ceres.htm Dwarf planet Ceres]." ''Views of the Solar System'', 2007. Accessed January 22, 2008.
* "[http://planetary.org/explore/topics/asteroids_and_comets/ceres.html Asteroid 1 Ceres]." ''The Planetary Society''. Accessed January 22, 2008.
* Carey, Bjorn. "[http://www.space.com/scienceastronomy/050907_ceres_planet.html Largest Asteroid Might Contain More Fresh Water than Earth]." <http://www.space.com>, September 7, 2005. Accessed January 22, 2008.
* Parker, Joel William, Thomas, Peter C., McFadden, Lucy A., Mutchler, M., and Levay, Z. "[http://hubblesite.org/newscenter/archive/releases/2005/27/ Largest Asteroid May Be 'Mini-Planet' with Water Ice]." ''The Hubble Site'', September 7, 2005. Accessed January 22, 2008.
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