Eris is a dwarf planet. It was put into a special classification of dwarf planets, a plutoid, along with the demoted Pluto.
It orbits the sun beyond the radius of the eight official planets, at a distance about twice that of Pluto.
Infrared images have shown that Eris is actually larger than Pluto.
While the eight planets have almost the same tilt when orbiting around the sun, Eris is tilted 44 degrees from the plane of the planets.
Eris has a moon called Dysnomia. That moon circles the dwarf planet in almost a circular orbit in about 16 days.