Eris (Dwarf Planet/Plutoid)

Eris [1] named after the Greek goddess of strife and discord is a late addition to the solar family. It was discovered by M. E. Brown, C. A. Trujillo and D. L. Rabinowitz on January 5, 2005, from images taken October 21, 2003, and officially designated as a "dwarf planet" [2] by the International Astronomical Union on August 24, 2006, and as a "plutoid" [3] on June 11, 2008. [4]

A highly eccentric orbit places Eris as close as 37.8 AU from the Sun at perihelion and as far as 97.6 AU from the Sun at aphelion (in more conventional measurement 5.65 to 14.6 billion kilometers). Earth by comparison orbits at 1 AU or (approximately) 150 million kilometers.

Eris is the largest of the dwarf planets (still open to debate). It is approximately 2,326 km in diameter (this latest and most accurate determination of its size the result of measurements taken by French astronomers during a stellar occultation in November 2010) and 27% more massive than Pluto.

Spectroscopic analysis of the new planet seems to indicate the presence of methane ice and it's possible that at its closest approach to the Sun the methane sublimates and forms a tenuous atmosphere. Surface temperatures vary between -232 and -248 degrees Celsius.

To date Eris has one known moon: Dysnomia.

[1] Xena, inspired by the television show Xena: Warrior Princess was an early moniker for Eris although Persephone the wife of Pluto was also considered.

[2] A "dwarf planet" is a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round shape), (c) has not cleared the neighborhood around its orbit and (d) is not a satellite.

[3] A "plutoid" is a trans-Neptunian dwarf planet.

[4] Due to its position in the "scattered disk" [5] Eris is also classified as a scattered disk object or SDO.

[5] The scattered disk is an area of rock-ice objects with highly erratic trajectories (steeply inclined to the plane of the ecliptic) orbiting beyond but approaching Neptune at perihelion (30 AU to as much as 150 AU at aphelion) and therefore subject to continued perturbation by that giant's gravity. As is obvious there is overlap with the Kuiper belt [6] and in fact some astronomers consider the scattered disk to be not separate but merely an extension of that more densely populated inner region.

[6] The Kuiper belt is a region of the outer Solar System populated by billions of rock-ice objects. It reaches from the orbit of Neptune (30 AU) outward to approximately 55 AU.

HOME TABLE OF CONTENTS COPYRIGHT INFORMATION SITE MAP <<PREVIOUS NEXT>>