Discovery of Dwarf Planet Eris

Date: January 5, 2005 • Location: Aguanga, United States

The dwarf planet Eris was discovered by a team using images from the Samuel Oschin telescope at Palomar Observatory.

A dwarf planet is a small planetary-mass object that is in direct orbit around the Sun, massive enough to be gravitationally rounded, but insufficient to achieve orbital dominance like the eight classical planets of the Solar System. The prototypical dwarf planet is Pluto, which for decades was regarded as a planet before the "dwarf" concept was adopted in 2006. Many planetary geologists consider dwarf planets and planetary-mass moons to be planets, but since 2006 the IAU and many astronomers have excluded them from the roster of planets.