Planet Eris

Planet Eris, also designated 136199 Eris and formerly 2003 UB313, is the largest known dwarf planet in the solar system and the ninth largest body orbiting the Sun directly. It is between 2,400 and 3,000 kilometres (1,490 to 1,860 miles) in diameter and 27% more massive than Pluto.

Eris was discovered in 2005 by a Mount Palomar-based team led by Mike Brown. It is a trans-Neptunian object (TNO) native to a region of space beyond the Kuiper belt known as the scattered disc. Eris has one moon, named Dysnomia; recent observations found no evidence of further satellites. Their current distance from the Sun is some 97 AU, or roughly three times that of Pluto. With the exception of some comets, the pair are currently the most distant known bodies in the Solar System.

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, motivated the International Astronomical Union (IAU) to define the term "planet" for the first time. Under a new definition approved on August 24, 2006, Eris was designated a "dwarf planet" along with Pluto and Ceres.

Name
The planet was sometimes called Planet X (both representing the unknown and the number 10). It was informally called Xena and its moon Gabrielle, after characters in the Xena television show. It was also called Lila, which could either be a reference to discover Brown's daughter Lilah or to a term for a small planet.

It eventually got its official name of 136199 Eris after the goddess Eris, a personification of strife and discord who is the primary deity of the Discordians. This represented the strife caused by the demotion of Pluto to a dwarf planet. The name was assigned on September 13, 2006, which Discordians know as Mass of Planet Eris as as Mass of Eristotle (the dwarf Discordian oracle Eristotle was born on September 13, 1752).

The naming of the planet as Eris began as a Jake by Professor Mu-Chao:

We should start a Jake campaign to get the new planet named Eris, or more like "Discordia" to keep with the Roman naming scheme....

This planet was obviously not invited to the party and has been hiding out there well into our Space Age waiting to cause mischief. Also, there are no hot dog buns that far from the sun. I think the choice is obvious.

Lets just hope she doesn't roll any golden astroids[sic] our way.

This Jake became known as 'The Jake that Changed a World.'

Some Discordians, including the Harmonians and Ek-sen-trik Discordians, refer to Eris' moon Dysmonia as Shamlicht.