Eris

Eris, designated (136199) Eris or 136199 Eris is the largest known dwarf planet in the solar system and the ninth largest body orbiting the Sun. 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. Mike Brown, who led the Mount Palomar-based discovery team, announced in April 2006 that the Hubble Telescope has measured Eris's diameter to be slightly larger than that of Pluto.

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. Brown has since stated his approval of the new "dwarf planet" label.

The average diameter of Eris is 2,326 km, in which it is slightly same size as Pluto. The average distance from Sun is 10,125,000,000 kilometers and has an orbital period of 556.7 years, and currently lies at almost its maximum possible distance from the Sun (aphelion). The diameter of Eris has been measured to be 2,326 kilometres using images from the Hubble Space Telescope. The brightness of an object depends both on its size and the amount of light it reflects. The approximate mass of Eris is 1.67 x 10^22 kg, lighter than Pluto.