What is Ceres like?
Ceres is the largest object in the asteroid belt, a dwarf planet about 940 kilometres across, with a crust of rock, ice and salts and bright patches of sodium carbonate.
Ceres was the first asteroid discovered, found by the Italian astronomer Giuseppe Piazzi on 1 January 1801. It was considered a planet for some decades, then an asteroid, and since 2006 has been classified as a dwarf planet.
Size and shape. Ceres is about 940 kilometres across, nearly round, and contains about a quarter to a third of the mass of the whole asteroid belt.
Dawn's discoveries. NASA's Dawn spacecraft orbited Ceres from 2015 to 2018. It found a dark surface covered in craters, with bright spots in some craters. The brightest, in Occator crater, about 92 kilometres across, are deposits of sodium carbonate and other salts, left when briny water rose to the surface and evaporated. Some deposits appear geologically young, suggesting brine may still exist below the surface.
Interior. Ceres has a low density, about 2.2 grams per cubic centimetre, suggesting a mixture of rock and water ice or water-bearing minerals. It may have a muddy interior and possibly a layer of brine deep below.
Ahuna Mons. A mountain about 4 kilometres high, Ahuna Mons, appears to be a cryovolcano, made by the eruption of icy, salty material.
Organic matter. Dawn detected organic compounds in some areas.
Meteorites. No meteorites have been confirmed as coming from Ceres. Its surface resembles carbonaceous chondrites in some respects, especially CM and CI types, but with differences.
Ceres is a fascinating world that blurs the line between asteroid and icy moon.