The first trans-Neptunian object found with a diameter larger than that of Pluto, and the largest of the new class of dwarf planets; also known as minor planet (136199). Eris is about 2400 km in diameter and has a mean density of 2.3 g/cm3 and a mass 1.27 times that of Pluto. It has a satellite, Dysnomia, about 0.1 its diameter, which orbits it every 15.8 days. It was discovered in 2005 by the American astronomers Michael Edwards Brown (1965– ), Chadwick Aaron Trujillo (1973– ), and David Lincoln Rabinowitz (1960– ). Its orbit has a perihelion of 38.54 AU, aphelion 97.56 AU, inclination 43°.9, and period 561.35 years, placing it among the scattered-disk objects.
Subjects: Astronomy and Astrophysics.