Ninth planet (disambiguation)

 Ninth planet is a concept related to planets beyond Neptune.

Ninth planet or Planet Nine may also refer to:

Astronomy

 * Neptune, sometimes considered the ninth planet from 1979–1999 when Pluto was classified as a planet and was temporarily closer to the Sun than Neptune
 * Planet Nine, hypothetical ninth planet in the outer Solar System
 * Pluto, considered the ninth planet from its 1930 discovery until it was reclassified as a dwarf planet in 2006 (except 1979–1999, see above)

Music

 * Planet 9 (record label), founded by Mya