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[[Image:Eris and Dysnomia.jpg|thumb|200px|right|[[Eris]] and its satellite, [[Dysnomia]].]]A '''dwarf planet''' is a satellite of the [[Sun]] that meets the following criteria now set by the [[International Astronomical Union]]:{{Cquote|(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 neighbourhood around its orbit, and (d) is not a satellite.<ref>"[http://www.iau.org/iau0602.423.0.html IAU0602: the Final IAU Resolution on the Definition of 'Planet' Ready for Voting]," ''International Astronomical Union'', 2005. Accessed January 14, 2008.</ref>}}

A '''dwarf planet''' is a satellite of the [[Sun]] that meets the following criteria now set by the [[International Astronomical Union]]:{{Cquote|(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 neighbourhood around its orbit, and (d) is not a satellite.<ref>"[http://www.iau.org/iau0602.423.0.html IAU0602: the Final IAU Resolution on the Definition of 'Planet' Ready for Voting]," ''International Astronomical Union'', 2005. Accessed January 14, 2008.</ref>}}

The definition was adopted on 24 August, 2006, as part of a three-way classification of bodies orbiting the Sun.<ref>http://www.iau.org/static/resolutions/Resolution_GA26-5-6.pdf</ref> This classification defines [[planet|planets]] as "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 and (c) has cleared the neighborhood around its orbit."

The definition was adopted on 24 August, 2006, as part of a three-way classification of bodies orbiting the Sun.<ref>http://www.iau.org/static/resolutions/Resolution_GA26-5-6.pdf</ref> This classification defines [[planet|planets]] as "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 and (c) has cleared the neighborhood around its orbit."

== Eris ==

== Eris ==

: ''Main Article: [[Eris]]''

: ''Main Article: [[Eris]]''

The concept of "dwarf planet" properly dates to the discovery of the scatter-disk object named [[Eris]] on January 5, 2005. With the confirmation of the identification of Eris, a formal debate began on the subject of what does, and what does not, constitute a [[planet]]. The community of [[Astronomy|astronomers]] decided that relying on history and tradition simply would not serve. The eight celestial bodies that now remain under the present definition of ''[[planet]]'' do not share their orbits with any other objects. The objects now called dwarf planets do not have this distinction. And yet these objects are significantly heavier than mere [[asteroid]]s, in that they are so heavy that their own weight, and more particularly their own gravity, forces them to assume the round or nearly-round shape that all planets have.

The concept of "dwarf planet" properly dates to the discovery of the scatter-disk object named [[Eris]] on January 5, 2005. With the confirmation of the identification of Eris, a formal debate began on the subject of what does, and what does not, constitute a [[planet]]. The community of [[Astronomy|astronomers]] decided that relying on history and tradition simply would not serve. The eight celestial bodies that now remain under the present definition of ''[[planet]]'' do not share their orbits with any other objects. The objects now called dwarf planets do not have this distinction. And yet these objects are significantly heavier than mere [[asteroid]]s, in that they are so heavy that their own weight, and more particularly their own gravity, forces them to assume the round or nearly-round shape that all planets have.