Eris (pronounced EAR-us or AIR-us) is the largest known dwarf planet in the solar system, with a diameter of about 2500 kilometers and a mass that is 27% greater than Pluto's. It was first spotted in January 2005. Eris's orbit is beyond the Kuiper belt.
Since Eris orbits beyond the orbit of Neptune, it is a trans-Neptunian object. Since it is a trans-Neptunian dwarf planet, it is a plutoid.
It takes Eris 557 years to orbit the sun. The orbit is highly elliptical, with an aphelion 97.5 AU from the Sun but a perihelion only 37.9 AU from the Sun. Its orbit is tilted by 44° relative to Earth's orbit.
Methane is known to be present on Eris.
Eris has only one known moon, Dysnomia, which has an estimated diameter of between 100 and 250 kilometers.