1 Ceres was considered a planet from 1801 until the 1860s. Pluto was considered a planet from 1930 to 2006. A 2006 IAU proposal to define the term ""planet"" would have reclassified Ceres as a planet, but this resolution was modified before its ratification in late August 2006. The modification instead placed Ceres, Pluto, and Eris in the newly created category of ""dwarf planet"".