posted August 25, 2006 03:42 PM            

* is in orbit around the Sun,
* has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape,
* has not "cleared the neighbourhood" around its orbit,
* is not a satellite of a planet, or other nonstellar body.

This definition reclassified Pluto from a planet to a dwarf planet because it has not cleared the neighbourhood of its orbit (the Kuiper Belt).

ist of dwarf planets

The IAU has officially identified three celestial bodies that immediately receive "dwarf planet" classification[1]:
Dwarf planets Name Solar System region Category Diameter Mass
Ceres Asteroid belt Asteroid 975×909 km 9.5 × 1020 kg
Pluto Kuiper belt Plutino 2306±20 km ~1.305 × 1022 kg
2003 UB313 ("Xena") Scattered disc Scattered disc object 2400 km ± 100 km unknown

Additionally, there are several bodies potentially qualifying as "dwarf planets,". Among these the following are known or thought to be greater than around 750 km in diameter:
Possible dwarf planets Name Category Diameter Mass
2005 FY9 ("Easterbunny") Cubewano 1600 – 2000? km unknown
Orcus Plutino 840 - 1880 km 6.2 - 7.0 × 1020 kg
Sedna Scattered disc object 1180–1800 km 1.7-6.1 × 1021 kg
2003 EL61 ("Santa") Cubewano ~ 1500 km ~4.2 × 1021 kg
Quaoar Cubewano 989 - 1346? km 1.0-2.6 × 1021 kg
Charon
(satellite of Pluto) Plutino 1207 km ± 3 km (1.52±0.06)×1021 kg
2002 TC302 Scattered disc object ≤ 1200 km unknown
Varuna Cubewano ~936 km ~5.9 × 1020 kg
2002 UX25 Cubewano ~910 km ~7.9 × 1020 kg
2002 TX300 Cubewano <900 km unknown
Ixion Plutino <822 km unknown
2002 AW197 Cubewano 700±50 km unknown

Despite this new classification scheme other terms such as asteroid and Kuiper Belt Object continue to apply.[citation needed] These terms are based on a body's location in the Solar System and/or its composition and history. Ceres continues to be the largest asteroid and Pluto continues to be a Kuiper Belt object despite their classification as dwarf planets also. One could consider both categories being subdivided into dwarf planet members and small solar system body members.

http://en.wikipedia.org/wiki/Dwarf_planet