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Astronomy Index

Dwarf Planets

Eris Discovery Images [Mike Brown, CalTech]

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.

Dwarf planets:
  • 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.
As of August 2007, only three dwarf planets have been recognised: Eris, Pluto and Ceres.

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Last updated: 15th August 2007
Michael Gallagher