Once qualified as the largest known asteroid, Ceres is now classified as a dwarf planet (2006 IAU General Assembly). It is approximately 950 km across, and resides with tens of thousands of asteroids in the main asteroid belt; it is the largest body of the belt. Its mass is 9.4 x 10^20 kg, its rotation period 9.074 hours, its orbital period 4.60 years, and its semi-major axis 2.767 AU. NASA's Dawn spacecraft, which was placed in orbit around Ceres in 2015, has mapped its surface in great detail. Dawn discovered very bright spots, which reflect far more light than their much darker surroundings. The most prominent of these spots lie inside the crater Occator and suggest that Ceres may be a much more active world than most of its asteroid neighbors.