Eris is the largest known dwarf planet in the solar system.
It is a trans-Neptunian object (TNO), orbiting the Sun in a region of space known as the scattered disc, just beyond the Kuiper belt, and accompanied by at least one moon, Dysnomia.
Eris' size resulted in its discoverers and NASA labelling it the solar system's tenth planet.
This, along with the prospect of other similarly sized objects being discovered in the future, stimulated the International Astronomical Union (IAU) to define the term "planet" more precisely.
Under a new definition approved on August 24, 2006, Eris was designated a "dwarf planet" along with Pluto and Ceres.