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Ceres (2.77 AU (414 million km; 257 million mi)) is the largest asteroid, a protoplanet, and a dwarf planet. It has a diameter of slightly under 1,000 km (620 mi), and a mass large enough for its own gravity to pull it into a spherical shape. Ceres was considered a planet when it was discovered in 1801 and was reclassified to asteroid in the 1850s as further observations revealed additional asteroids. It was then reclassified again as a dwarf planet in 2006 when the IAU definition of planet was created.
