Eris

In 2005, astronomers discovered what they thought to be a new planet in the Solar system. The object, which has been named Eris, is currently 97 astronomical units away, putting it more than twice the distance of the dwarf planet Pluto and therefore the farthest visible object in the solar system.

Although we cannot yet be sure, we think that Eris is a rocky/icy object about one and a half times the size of Pluto.

Following its discovery there was debate amongst other astronomers as to whether the new object could be called a planet, and this discussion eventually led to Pluto being de-classified as a proper planet in 2006, 76 years after it was first discovered.

The problem is that Eris's orbit is highly inclined or tilted (44°) to the orbits of the other planets in the solar system - as is Pluto's, which also has an inclined orbit (17°). This suggests that the object did not form in the same way as the planets and is simply a large lump of rock that was somehow captured into its highly eccentric 557 year orbit around the Sun.

Eris is now officially referred to as a plutoid. These are dwarf planets that circle the Sun beyond the orbit of Neptune.

Facts and Figures
Average Orbit	10,120,000,000 km from the Sun or 67.67 AU
Orbital Inclination	44 °C
Radius	1300 km
Mass	1.7 x 1022 kg or 0.003 Earths
Length of Year	557 Earth years
Length of Day	Unknown
Surface Gravity	0.08 g
Surface Temperature	about -230 °C