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Ceres
Symbol	⚳
Date of discovery	January 1, 18011 January 1801 16 Teveth 5561 He 15 Teveth 5804 AM[1]
Name of discoverer	Giuseppe Piazzi[1]
Name origin	Roman goddess of agriculture[1]
Orbital characteristics
Celestial class	Dwarf planet
Primary	Sun
Order from primary	5
Perihelion	2.54670746 AU380,982,011.529 km 236,731,246.725 mi[2]
Aphelion	2.986856037 AU446,827,301.132 km 277,645,612.828 mi[2]
Semi-major axis	2.76678175 AU413,904,656.555 km 257,188,429.916 mi[2]
Titius-Bode prediction	2.8 AU
Orbital eccentricity	0.07954162[2]
Sidereal year	1680.973163 da4.602 a[2]
Avg. orbital speed	17.882 km/s64,375.2 km/h 11.111 mi/s 40,000.895 mph
Inclination	10.586404°0.185 rad 11.763 grad to the ecliptic[2]
Rotational characteristics
Sidereal day	9.075 h0.378 da[2]
Rotation speed	0.091584 km/s329.702 km/h 0.0569 mi/s 204.868 mph[2]
Axial tilt	3°0.0524 rad 3.333 grad
Physical characteristics
Mass	9.47 * 1020 kg1.584675e-4 M⊕ 0.0129 M☾[3]
Mean density	2,093.95 kg/m³2.094 g/ml 130.721 lb/ft³[3]
Mean radius	476.2 km295.897 mi[2]
Equatorial radius	487.3 km302.794 mi
Polar radius	454.7 km282.537 mi
Surface gravity	0.2787 m/s²0.914 ft/s² 0.0284 g
Escape speed	0.5152 km/s1,854.72 km/h 0.32 mi/s 1,152.47 mph[3]
Surface area	2,849,631 km²1,100,248.68 mi² 0.00559 A⊕ 0.0752 A☾
Mean temperature	167 K-106.15 °C -159.07 °F 300.6 °R
Maximum temperature	239 K-34.15 °C -29.47 °F 430.2 °R
Number of moons	0
Composition	Rock and water
Color	#FFC9A0
Albedo	0.090[2]

Ceres, formerly known as Asteroid 1 Ceres, is the first identified object in the asteroid belt, and the largest. 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.

Contents 1 Discovery 2 Status 3 Composition 4 Satellites 5 Observation and Exploration 6 References 7 Related Links

Discovery

Piazzi was searching for the "missing planet" that, according to the Titius-Bode 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 asteroids 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 planets—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.^[4][5] Findings supporting the water-ice theory include:

1. Most objects having hydrostatic-equilibrium or round shape have differentiated, or layered, interiors.
2. 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.^[6]

Satellites

Ceres has no known satellites.

Observation and Exploration

Until today, the only observation of Ceres has been by telescope. Astronomers have inferred a remarkable number of the physical properties of Ceres from this observation, but wish to learn much more.

On September 27, 2007, the Dawn mission began officially with the launch of Dawn, the first rocket probe to visit the asteroid belt. The Dawn craft carries an ion engine that it will use on the second part of its journey after it makes rendezvous with Mars. Dawn's two targets are the asteroid Vesta and the dwarf planet Ceres.^[7][8]

References

Related Links

• Ceres by Wikipedia
• Hamilton, Calvin J. "Dwarf planet Ceres." Views of the Solar System, 2007. Accessed January 22, 2008.

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