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Planets and Solar System Bodies

In a decision passed by the International Astronomical Union General Assembly on August 24, 2006, the objects in the Solar System other than the Sun and natural satellites were divided into three separate groups: planets, dwarf planets and small solar system bodies. Under this classification, a planet is any body in orbit around the Sun that a) has enough mass to form itself into a spherical shape and b) has cleared its immediate neighborhood of all smaller objects. Eight objects in the Solar System currently meet this definition; they are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. Dwarf planet was a second and new classification. The key difference between planets and dwarf planets is that while both are required to orbit the Sun and be of large enough mass that their own gravity pulls them into a nearly round shape, dwarf planets are not required to clear their neighborhood of other celestial bodies. Three objects in the solar system are currently included in this category; they are Pluto (formerly considered a planet), the asteroid Ceres, and the scattered disc object Eris. The IAU will begin evaluating other known objects to see if they fit within the definition of dwarf planets. The most likely candidates are some of the larger asteroids and several Trans-Neptunian Objects such as Sedna, Orcus, and Quaoar. The remainder of the objects in the Solar System were classified as small solar system bodies (SSSBs).

 
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