Eris is a dwarf planet and a trans-Neptunian object (TNO). It is the second-largest known dwarf planet in the Solar System. Eris is slightly smaller than Pluto, but it is more massive (has more mass) than Pluto. It is a "scattered disc object" in the Kuiper belt, further out than Pluto. It is also called a "plutoid" because the IAU decided to rename all trans-Neptunian dwarf planets as plutoids. Eris orbits the sun once every 557 Earth years. It has an elliptical orbit, inclined at an angle of 44° between the plane of the orbit of the planet and the ecliptic, the plane containing Earth's orbital path. 