Eris (also known as (136199) Eris or 136199 Eris) is a dwarf planet of the solar system, the largest such object known to date, and the ninth largest body orbiting around the sun directly. It lies about 97 AU from the Sun and is therefore the most distant known object of the solar system. Its orbital period is of 556.7 years and is currently near its aphelion (97.56 AU); its perihelion is at 67.669 AU.
Eris is a trans-Neptunian Object (TNO) was discovered orbiting in the scattered disc, beyond the Kuiper belt, by Mike Brown's team at the Mount Palomar observatory on October 21st 2003. The Hubble Telescope measured his diameter in April 2006 to be approximately 2400 km, in other words, slightly larger than Pluto. It resulted in its discoverers and the NASA to label it as the tenth planet; that, and the prospect of finding many more such bodies in the future (which would eventually lead the number of planets to rise considerably) forced the International Astronomical Union to come up with a new and more precise definition of the term "planet", approved on August 24th 2006. This new definition ended up making Eris being classified among the new class of the "dwarf planets", along with Pluto and Ceres.
Eris was named after the Greek goddess of the same name, goddess of strife and discord. The name, assigned on September 13th 2006, was inspired by the unusually long period during which it was known under the provisional designation 2003 UB313, a delay resulting in the uncertainties over its planetary status, the rules to name planets and minor planets being different.