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Dwarf planet and largest known asteroid in the solar system and the first asteroid discovered, in 1801. Named after the Roman goddess Ceres, it revolves around the Sun in 4.61 Earth years, rotates once in 9.1 hours, and is about 585 mi (940 km) across. Its mass accounts for more than one-third the total mass of the asteroid belt. Ceres was designated a dwarf planet, a category of solar system object defined by the International Astronomical Union in August 2006.
This entry comes from Encyclopædia Britannica Concise. For the full entry on Ceres, visit Britannica.com.