Fifth planet may refer to:
Astronomy Jupiter, fifth planet from the Sun in the Solar System Fifth planet (hypothetical), any of various hypothetical planets thought to have existed Planet V, 2002 scientific proposal for a destroyed fifth planet Mars, fifth planet from Earth in the Ptolemaic geocentric model Ceres (dwarf planet), dwarf planet between Mars and Jupiter in the asteroid belt
Fiction Fifth Planet (novel), science fiction novel by Fred and Geoffrey Hoyle
See also