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Ceres is a dwarf planet in the asteroid belt between Mars and Jupiter, discovered in 1801 and reclassified as a dwarf planet in 2006. It has not cleaned up the neighborhood around its orbit and has a light atmosphere with surface frost. It makes up about a third of the mass in the asteroid belt and is the target of NASA’s Dawn mission, set to arrive in 2015.
Ceres is a dwarf planet and the largest body in the asteroid belt between Mars and Jupiter. Its dimensions are 975×909 km, making it about a quarter the size of the Moon. Ceres orbits 3 AU from the Sun. Its surface temperature averages about ~167 K (-159 °F), although at noon its temperature can rise to 235 K (about -38 °C). Ceres probably has a light atmosphere accompanied by surface frost.
When it was discovered by the Italian astronomer Giuseppe Piazzi on January 1, 1801, Ceres was considered a planet, but in 1850 the astronomical community reclassified it as an asteroid. This designation remained for over 150 years, until 2006 when it was reclassified as a dwarf planet by the International Astronomical Union, along with the trans-Neptunian objects Pluto and Eris. Ceres is named after the Roman god of plants.
Ceres is not classified as a true planet because it does not meet one of the necessary criteria for planets; to have cleaned up the neighborhood around its orbit. Like Pluto and Eris, Ceres is nestled in an asteroid belt and hasn’t cleaned out its neighborhood. Despite its status as a dwarf planet, Ceres makes up about a third of the mass in the asteroid belt. Together with the three largest nearby asteroids, 4 Vesta, 2 Pallas and 10 Hygiea, Ceres makes up half of the total mass of the belt.
The powerful telescope images of Ceres fail to provide high resolution, and mysterious changes in Ceres’ features have been observed over the years. A dark spot observed in 1995 with the Hubble Space Telescope was named “Piazzi”, but subsequent observations with the high-resolution Keck Telescope found no trace of it. Hubble images from 2003 and 2004 show an enigmatic white spot, the nature of which is unknown. The white spot could be a reflective patch of ice.
No space probes have yet visited Ceres. On September 27, 2007, NASA launched its Dawn mission, which will explore asteroid 4 Vesta in 2011 before arriving at Ceres in 2015. After one year of orbit it will progressively approach, from 5,900 km to 700 km from the surface of Ceres .
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