Object Analysis

Eris is the most massive and second-largest known dwarf planet in the Solar System. It is a trans-Neptunian object (TNO) in the scattered disc and has a high-eccentricity orbit. It was discovered in January 2005 by a team led by Michael Brown.

Initially nicknamed "Xena," Eris is slightly smaller than Pluto by diameter but is 27% more massive, indicating it is much denser and rockier. Its discovery precipitated the demotion of Pluto, as astronomers realized there could be dozens of Eris-sized objects in the outer solar system.

Eris is extremely reflective (albedo 0.96), likely because its atmosphere freezes out onto the surface as a bright white glaze when it is far from the Sun. It has one moon, Dysnomia. It takes 558 years to complete one orbit around the Sun.