Eris,  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 on October 21,
2003, and officially designated as a "dwarf planet"  by the
International Astronomical Union on August 24, 2006, and as a "plutoid"
 on June 11, 2008. 
highly eccentric orbit places Eris as close as 37.9 AU from the Sun
perihelion and as far as 97.65 AU from the Sun at aphelion (in
conventional terms 5.65 to 14.6 billion kilometers). Earth
comparison orbits at an average distance of 1 AU or approximately 150 million kilometers.
With a diameter of approximately 2,326 kilometers Eris
is the second largest, after Pluto, of the dwarf planets (though 27% more massive). This latest and most
accurate determination of its size is the result of measurements taken by
French astronomers during a stellar occultation in
analysis of the dwarf 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
are estimated to vary between -217.2 and -243.2 degrees Celsius.
date Eris has one known moon: Dysnomia.
"Xena," inspired by the lead character in the television show Xena:
Warrior Princess, was an
early moniker for Eris although Persephone the wife of
Pluto was also considered.
 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.
"plutoid" is a trans-Neptunian dwarf planet.
to its extreme elliptical orbit, it's a split decision, Eris is referred
to as a KBO (Kuiper Belt object) by NASA and an SDO
object)  by the IAU. Which is correct? An
interesting head-scratcher for the experts. My view on the subject: although often referred to as a KBO it's technically an SDO.
scattered disk is an area of rock-ice objects with highly
inclined to the ecliptic plane) 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  and in fact many
astronomers consider the scattered disk to be not separate but rather
an extension of that more densely populated inner region.
 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.
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