List of hypothetical planetary objects

A hypothetical planetary object is a planet, natural satellite or similar body whose existence is not known, but has been inferred from observational scientific evidence. Over the years a number of hypothetical planets have been proposed, and many have been disproved. However, even today there is scientific speculation about the possibility of planets yet unknown that may exist beyond the range of our current knowledge.

Our solar system is by no means fully mapped and charted. Much of its territory is still unknown, and many astronomers have hypothesized from indirect observation that other substantial objects could still exist undetected in its farthest reaches.

*Chiron, a moon of Saturn supposedly sighted by Hermann Goldschmidt in 1861 but never observed by anyone else.
*Mercury's moon, hypothesised to account for a sudden burst of radiation detected by "Mariner 10". Disproved by the spacecraft's subsequent flyby. An object thought to be orbiting Mercury eventually revealed itself to be the star 31 Crateris.
*Neith, a purported moon of Venus, falsely detected by a number of telescopic observers in the 17th and 18th centuries. Now known not to exist, the object has been explained as a series of misidentified stars.
*Nemesis: a large planet or brown dwarf whose existence is suggested by physicist Richard A. Muller, based on purported periodicities in mass extinctions within Earth's fossil record. Its regular passage through the Solar System's Oort cloud would send large numbers of comets towards Earth, massively increasing the chances of an impact.
*Phaeton, a planet situated between the orbits of Mars and Jupiter whose destruction supposedly led to the formation of the asteroid belt. Nowadays this hypothesis is considered unlikely, since the asteroid belt has far too little mass to have resulted from the explosion of a large planet.
*Planet V, a planet thought by John Chambers and Jack Lissauer to have once existed between Mars and the asteroid belt, based on computer simulations.
*Planet X: A hypothetical planet beyond Neptune. Initially employed to account for supposed discrepancies in the orbit of Uranus, it has been disproved. The concept has been re-applied to account for subsequent observations, however.
*Theia, a Mars-sized impactor believed to have collided with the Earth roughly 4 billion years ago; an event which created the Moon.
*Themis, a moon of Saturn which astronomer William Pickering claimed to have discovered in 1905, but which was never seen again. [ [http://www.nineplanets.org/hypo.html#sat Hypothetical Planets ] ]
*Vulcan: A hypothetical planet once believed to exist inside the orbit of Mercury.
*Vulcanoids: a ring of asteroids which may exist within a gravitationally stable region inside Mercury's orbit.

ee also

*List of unconfirmed exoplanets
* Theoretical planetology

References