Planet X

+**Planet X** (slug: planet_x) is the historical name for a hypothetical major planet beyond [Neptune](/wiki/Neptune). Once sought to explain perceived [orbital anomalies](/wiki/Orbital_Anomalies) in the outer Solar System, its elusive nature pushed the boundaries of planetary discovery, though modern searches continue for a true ninth planet.

+## See also

+- [Ninth Planet](/wiki/Ninth_Planet)

+- [Trans-Neptunian](/wiki/Trans-Neptunian)

+- [Kuiper Belt](/wiki/Kuiper_Belt)