Ceres
Key facts
- What it is
- Dwarf planet in the main belt
- Size
- About 940 km across
- Discovered
- 1801, by Giuseppe Piazzi
- Spacecraft
- Dawn (in orbit 2015–2018)
- Orbit group
- Main-belt Asteroid
- Average distance from the Sun
- 2.77 au (about 410 million km)
- Time to go round the Sun
- 4.6 years
- Closest and farthest from the Sun
- 2.55 to 2.99 au
- Tilt of its orbit
- 10.6°
- Spins once every
- 9.1 hours
An au (astronomical unit) is Earth's average distance from the Sun, about 150 million km. Orbit figures are from open tracking data, figures last updated 1 Nov 2026.
Ceres was the first object found in the gap between Mars and Jupiter. Giuseppe Piazzi spotted it from Palermo on the first night of 1801, and for half a century it was counted as a planet. Today it is called a dwarf planet: big enough for its own gravity to pull it into a round shape, but sharing its orbit with countless smaller bodies. At about 940 kilometres across, it holds roughly a third of all the mass in the asteroid belt.
NASA's Dawn spacecraft orbited Ceres from 2015 to 2018 and found a world quite unlike a dry rock. Its surface is rich in clay minerals, carbonates and ammonia-bearing compounds, all signs that liquid water once worked through its interior. The famous bright patches in Occator crater turned out to be deposits of sodium carbonate, salts left behind when salty water seeped up from below and evaporated into space. A lone mountain, Ahuna Mons, about 4 kilometres high, appears to have been pushed up by a slow, icy kind of volcanism.
Gravity measurements showed that Ceres is only partly separated into layers. A rocky interior is wrapped in a mantle of ice, salts and rock, and a layer of brine may survive deep down even now.
No meteorite has been firmly traced to Ceres. Its surface chemistry is closest to the carbonaceous chondrites, the dark, water-altered meteorites, which suggests that Ceres and those meteorites' parent bodies formed from similar material. Ceres is a reminder that the asteroid belt contains watery worlds as well as stony and metallic ones.