Planet X

Do you believe that there is Planet X ?

In astronomy, Planet X is a large hypothetical planet beyond Neptune. It was postulated to explain apparent discrepancies in the orbits of the gas giants, especially those of Uranus and Neptune. Those discrepancies were resolved by measurements made in the 1980s.

The "X" in the name represents an unknown and is pronounced as the letter, as opposed to the Roman numeral for ten. At the time of its conception there eight known planets in the solar system; it was accordingly counted as a "ninth planet" in its initial decades, and then as a "tenth planet" from 1930 until the theory's demise in the early 1990s, and its is now generally accepted in the astronomical community that Planet X, as originally envisioned, doesn't' exist.

Although Pluto was discovered as a result of the search for Planet X, it is not considered Planet X. Neither is, Eris, even though it was at one point considered for reclassification as a planet under a proposal outlined by the International Astronomical Union. In popular culture, "Planet X" has become a stand-in term for an undiscovered planet in the solar system. The term has also been appropriated by pseudoscientific theorists such as Nancy Lieder and Marshall Masters.

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