Planet

A planet, as defined by the International Astronomical Union is a celestial body meeting the following requirements:

For a body in the solar system:
 * 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 cleared the neighbourhood around its orbit

For a body within another planetary system:
 * is in orbit around a star or the remnants of one
 * has a mass below the limiting mass for thermonuclear fusion of deuterium
 * is above the minimum mass/size requirement for planetary status in the Solar System.

Therefore, the solar system counts 8 planets: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. In addition to these eight, three dwarf planets are also known: Ceres, Pluto and Eris. As for extrasolar planets, 210 are known as of February 8th 2007.


 * Telluric planet
 * Jovian planet
 * Extrasolar planet
 * Interstellar planetary mass object
 * Dwarf planet
 * Hot Jupiter