Zetas And Planet X (Paranormal) 

Planet X is a large hypothetical planet beyond that of Neptune. The scientific basis of the Planet X hypothesis was broadly discounted in the early 1980s and today no significant portion of the scientific community believes it to exist.

The "X" mentioned 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 were eight known planets in the solar system; its existence, first as a ninth planet, and then from 1930 until its demise 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 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 (see 2006 redefinition of 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.

Source: Wikipedia