Dwarf planets. Three dwarf planets in a row showing their comparative sizes. From left to right: Ceres, Pluto, and Eris. Pluto, a Kuiper object, was demoted to the status of dwarf planet in 2006 when the International Astronomical Union (IAU) reviewed its status in light of the recently discovered Eris, also a Kuiper object. Eris was discovered in 2003 and is now the largest of the known dwarf planets. At the same time Pluto suffered its demotion, the object Ceres was promoted from asteroid to dwarf planet.