Reference Article

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Planet

The International Astronomical Union defines "planet" as a celestial body that, within the Solar System that 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; and has cleared the neighbourhood around its orbit; or within another system, it is in orbit around a star or stellar remnants; has a mass below the limiting mass for thermonuclear fusion of deuterium; and is above the minimum mass/size requirement for planetary status in the Solar System.

Our solar system is thus considered to have eight planets: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune.

Under a separate resolution, it is also considered to have three dwarf planets: Ceres, Pluto, and Eris.

There have been more than two hundred planets discovered orbiting other stars to date.

Note: This article excerpts material from the Wikipedia article "Planet", which is released under the GNU Free Documentation License.

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