Planet X

::This article is about the hypothetical planet.

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::Planet X can also mean Planet 10. See tenth planet

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::For other meanings see Planet X (disambiguation)

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Planet X is a large hypothetical planet orbiting beyond the orbit of Neptune. (The X stands for unknown, rather than the Roman number 10.) Its existence, first as a ninth planet and after 1930 as a tenth, was postulated on the basis of apparent discrepancies in the orbits of the gas giants, especially those of Uranus and Neptune. Those discrepancies have largely been resolved by modern measurement, removing the basis for Planet X.

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Although Pluto was discovered as a result of the search for Planet X, it is not Planet X. The newly discovered Kuiper Belt object 2003 UB313 is not Planet X either, although the International Astronomical Union may in the future designate it as a tenth planet.

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In popular culture, "Planet X" has become a generic stand-in term for an undiscovered planet in the solar system. Its use by scientists, however, is exclusively in reference to the particular hypothesis discussed in this article.

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Hypothetical planet: Hypothetical planets are planets that have been suggested as possibly existing (or have been believed to exist), but have never been proven to actually exist. This includes ones that have later been proven not to exist....

Neptune: :This article is about the planet. For the Roman god, see Poseidon. For other meanings, see Neptune (disambiguation)....

Orbit: In physics, an orbit is the gravitationally curved path of one object around a point or another body, for example the gravitational orbit of a planet around a star....

Planet X related Images and Photos (experimental)

Planet Earth (1974) (DVD)	Planet 51	Planet Express	Planet Stories
Red Planet (DVD) (Rpkg)	Red Planet (BD)	Blue Planet (IMAX) (BD)	Blue Planet (IMAX) (DVD)
Planet Landscape	Human Planet (DVD) (2010)	Red Planet	Frozen Planet (DVD)