1 Ceres
| Orbital characteristics | |
|---|---|
| Orbit type | Main belt |
| Semimajor axis | 2.767 AU |
| Eccentricity | 0.0789 |
| Orbital period | 4.60 year |
| Inclination | 10.58 ° |
| Physical characteristics | |
| Diameter | 960x932 km |
| Mass | 8.7×1020 kg |
| Density | 2.0 g/cm3 |
| Rotation period | 9 h 4 min |
| Spectral class | G |
| Albedo | 0.11 |
| History | |
| Discoverer | G. Piazzi, 1801 |
1 Ceres (asteroid 1 — See-reez) was the first asteroid to be discovered, with a diameter of 960x932 km[1], and a surface area of 1,800,000 km2. It was discovered on January 1, 1801, by Giuseppe Piazzi, and originally named Ceres Ferdinandea after the Classical Greek and Sicilian goddess of plants and motherly love and King Ferdinand IV of Naples and Sicily. The Ferdinandea part was dropped for political reasons.
Ceres is the largest known asteroid in the traditional asteroid belt between Mars and Jupiter. However the Kuiper belt is known to contain larger objects, including 28978 Ixion, 50000 Quaoar, 2004 DW and possibly Sedna (though many astronomers say Sedna is actually an inner Oort Cloud object). Pluto is also sometimes considered a Kuiper-belt object.
Ceres is unique in that its size and mass are sufficient to give it a spherical shape, much like a planet. Other large asteroids such as Juno and Vesta are known to be distinctly non-spherical. With a mass of 8.7×1020kg, Ceres comprises over one-third the 2.3×1021 kg estimated total mass of all the asteroids in the solar system. There are some indications that its surface is warm and that it may have a weak atmosphere and frost.
The chemical element Cerium (atomic number 58) was discovered in 1803 and took its name from the asteroid which had been found two years earlier.
In 2001, the Hubble Space Telescope imaged Ceres. The images are low resolution, but confirm that the asteroid is spherical, and show a dark spot on its surface, which is probably a crater.
NASA has currently approved a mission called Dawn to visit Ceres. The scheduled launch date is set for some time in 2006, with an orbital rendevous of the asteroid in 2016.