dwarf planet
Ceres and Pluto have been considered planets at time in the past. The discovery of other bodies in the asteroid belt led to the reclassification of Ceres in the mid-19th cent. as an asteroid. The discovery of other bodies beyond the orbit of Neptune that were similar in size to Pluto led to the declassification of Pluto as a planet in 2006, when the International Astronomical Union adopted the classification of dwarf planet.
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