Planet X is a large hypothetical planet orbiting beyond the orbit of Neptune. The X stands for "unknown", not the Roman number 10; there were only 8 known planets at the time. 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.

Although Pluto was discovered as a result of the search for Planet X, it is not Planet X. Kuiper Belt object 2003 UB₃₁₃ is not Planet X either, although its discoverers are pushing for the International Astronomical Union to designate it as a tenth planet.

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 below.

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Planet X - Twitter Search

Best fucking x mas ever!! Just got a fat gift card to dvd planet!! Gonna buy nothing but @criterion!!
SillyXGirl (Nikki) Fri, 25 Dec 2009 08:51:28 -0000
Best fucking x mas ever!! Just got a fat gift card to dvd planet!! Gonna buy nothing but @criterion!!
bodyguards and assassins (x) avatar (x) planet 51 (x) tinggal alvin and the chipmunks 2 nihh :p
jessicandriani (Jessica Andriani) Fri, 25 Dec 2009 08:47:42 -0000
bodyguards and assassins (x) avatar (x) planet 51 (x) tinggal alvin and the chipmunks 2 nihh :p
Even if I get no presents, I've still got @loveli, and that makes me the happiest man on the planet. She's the bestest in the world. X
philsherry (Phil Sherry) Fri, 25 Dec 2009 07:52:58 -0000
Even if I get no presents, I've still got @loveli, and that makes me the happiest man on the planet. She's the bestest in the world. X
Planet X 2012 - Learn About Planet X 2012 - http://tinyurl.com/y992cjm
niceReviewBlog (nikki webster) Fri, 25 Dec 2009 07:42:44 -0000
Planet X 2012 - Learn About Planet X 2012 - http://tinyurl.com/y992cjm
@ThatKevinSmith you have my sympathy sir. You must feel like Jim Cameron when Fox said he couldn't use "Blue Catpeople from Planet X"
CBrenchley (Chris brenchley) Fri, 25 Dec 2009 07:09:55 -0000
@ThatKevinSmith you have my sympathy sir. You must feel like Jim Cameron when Fox said he couldn't use "Blue Catpeople from Planet X"
rise n fall.. pertama x ngerasain pgen ngilang aja dr muka bumi ini.. (untuk tinggal di planet laen) hee #09memories
zanovarie (riskha rie pratiwi) Fri, 25 Dec 2009 07:02:26 -0000
rise n fall.. pertama x ngerasain pgen ngilang aja dr muka bumi ini.. (untuk tinggal di planet laen) hee #09memories

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