Eris is a dwarf planet that was only recently discovered. It is slightly larger than Pluto and is the biggest dwarf planet in the Solar System.

Diameter: 2400 km
Mass: 1.66 x 1022 kg
Composition: Rock
Orbit: 10,128,000,000 km from the Sun

Eris is the ninth-biggest object known to directly orbit the Sun and was first seen in 2003 at the Palomar Observatory in California by three scholars carrying out a survey. The team led by Professor Mike Brown included Chad Trujillo and David Rabinowitz. They were using a Samuel Oschin Schmidt telescope and focusing on the outer regions of the Solar System. Although they are credited with the discovery of Eris, it was not confirmed until 2005.

As initial indications suggested that Eris was bigger than Pluto, Eris was a contender to being named the tenth planet of the Solar System. It was during this time that clarification was sought on the true definition of a planet. As a result of this discussion, Eris was classified as a dwarf planet. Because Eris is bigger than Pluto, Pluto was therefore also downgraded to a dwarf planet. Other dwarf planets are Ceres, Haumea and Makemake. In 2005, after further investigations, Eris was found to have a moon which was called Dysnomia.

Eris was named in 2006. Eris was the Greek goddess of discord and strife. It was felt to be a very fitting name for a planet which sparked debate over the definition of a planet. Its moon, Dysnomia, is named after Eris’s daughter. Until Eris’s official name was revealed it was called Xena, the main character in the popular television series Xena: Warrior Princess.

Eris is a very cold planet because it orbits at such a great distance from the Sun. The icy conditions often cause the atmosphere to collapse. When this happens, an icy glace on the surface is formed. It shines brightly as the sun reflects off the surface. It is estimated that the temperature on Eris usually lies between -217 to -243 degrees Celsius. As Eris moves closer to the Sun, it is expected that the surface will eventually warm up and reveal a rocky surface.

Eris orbits the Sun every 557 years. Its plane lies outside of the Solar System’s plane, past the Kuiper Belt. The Kuiper Belt is an area containing a collection of icy objects and is past Neptune’s orbit.

The size of Eris makes it difficult to see clearly, so to get an estimate of its size, scientists studied its moon, Dysnomia. Knowing that Dysnomia orbits Eris in 16 days led them to conclude that Eris is smaller than Earth’s moon and is similar size to Pluto.

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