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Eris was named after the Greek goddess of discord and strife. Aptly named, the icy dwarf planet, Eris, has rattled the general model of our solar system. The object was discovered on January 5, 2005 by Mike Brown, Chad Trujillo and David Rabinowitz at Palomar observatory in the out reaches of the Kuiper belt. Its detection provoked debate about Pluto's classification as a planet. Eris is slightly larger than Pluto. So if Pluto qualified as a full-fledged planet, then Eris certainly should too. Astronomers attending the International Astronomical Union meeting in 2006 worked to settle this dilemma. In the end, we lost a planet rather than gaining one. Pluto was reclassified as a dwarf planet along with Eris and the asteroid Ceres, the most massive member of the asteroid belt. Eris is 10 billion miles from the sun and it has an orbital period of 556.7 years.

As a dwarf planet, Eris fulfills most of the criteria for being a planet with the exception that it doesn't have the gravitational pull, because of its size, to clear space surrounding it of other celestial bodies.

The atmosphere on Eris has been frozen for over a hundred years and this is a result of the dwarf planet's distance from the sun.

The largest known Kuiper Belt object and also the largest known dwarf planet according to a new classification scheme adopted by astronomers on August 24, 2006. 136199 Eris, formerly known as 2003 UB313, is further classified as a plutoid (a dwarf planet that orbits the Sun further out than Neptune) and a Scattered Disk object � a type of trans-Neptunian object believed to have been scattered from the main Kuiper Belt. Nicknamed "Xena" after the warrior princess in the TV series of that name before it acquired its official name in September 2006. Eris is larger than Pluto � but only just. Initial measurements had suggested that it might be as large as 3,000 km (1,875 miles) across; however, an image of the object sunsequently obtained using the Hubble Space Telescope revealed its diameter to be 2,400 ± 97 km(1,490 ± 60 miles).

Eris travels in a highly elliptical orbit, sharply inclined at angle of 44° to the plane of the ecliptic (the plane in which Earth's orbit lies), with a period of 558 years. This high inclination suggests that the object was thrown into its present orbit by an ancient encounter with Neptune. It is also the reason that Eris wasn't discovered earlier � most searches for new objects in the outer Solar System concentrate in and around the ecliptic plane.

The discovery was made by American astronomers Michael Brown of the California Institute of Technology, Chad Trujillo of the Gemini Observatory in Hawaii, and David Rabinowitz of Yale University using the Samuel Oschin Telescope at Palomar Observatory and the 8-meter Gemini North telescope on Mauna Kea. The object was first observed on Oct. 21, 2003, but the team did not see it move in the sky until looking at the same area 15 months later on Jan. 8, 2005. The announcement of the discovery of Eris, in July 2005, came shortly after that of 2003 EL61, which is probably somewhat smaller than Pluto.

Facts about Eris

  • First seen in 2003 but finally recognized in 2005

  • Highly elongated orbit around Sun lasting 558 years

  • Currently positioned some 14.5 billion km from Earth

  • Surface temperature of about -240°C

  • May have thin atmosphere when closest to Sun

  • Has one known moon

  • Eris is named for the Greek mythological goddess personifying discord

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