In 2006, the International Astronomical Union, faced with the prospect of discovery of
other larger than Pluto objects, decided to establish another category of Solar System objects: Dwarf Planets.
Pluto was assigned to this category, along with Eris, the most massive body to be discovered
in the Solar System in 150 years.
As of August 2007, only three dwarf planets have been recognised: Eris, Pluto and Ceres.
- orbit the Sun,
- have sufficient mass for their self-gravity to overcome rigid body forces so that they assumes a near-spherical shape,
- have not cleared the neighbourhood in the vicintiy of their orbits
- are not satellites of other bodies.