Ceres, illustration. Ceres is a dwarf planet, the only one that orbits in the asteroid belt. It is also an asteroid, the largest one known, and the first to be discovered, in 1801. The surface of Ceres is heavily cratered due to impacts from meteorites. It orbits the Sun at an average distance of 2.76 astronomical units (AU), and has a mean radius of 473 km - large enough for it to be spherical. It has been studied by the spacecraft Dawn, which entered into orbit around the mini-world in March 2015.