List of hypothetical Solar System objects
A hypothetical Solar System object is a planet, moon, or similar body in the Solar System 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.
The following is a list of hypothetical Solar System bodies in order of their distance and order from the Sun.
|Name||Theorized by||Details||Ruled out?|
|Vulcanoids||various||An asteroid belt within the orbit of Mercury in a gravitationally stable region. None have been detected. They may have originated as debris resulting from a collision between Mercury and another protoplanet, stripping away much of Mercury's inner crust and mantle.||Yes|
|Vulcan||Urbain Le Verrier||A planet less than 1,500 km across and red in color believed to exist inside the orbit of Mercury. Initially proposed as the cause for the perturbations in the orbit of Mercury, some astronomers spent many years searching for it, with many instances of people claiming to have found it. The perturbations in Mercury's orbit were later accounted for via Einstein's General Theory of Relativity.||Yes|
|Intra-Mercurial super-Earth||Rebecca G. Martin and Mario Livio||The lack of vulcanoids led to a suggestion in 2016 that a super-Earth planet that once orbited the Sun closer to Mercury was able to clear its neighborhood before spiraling down into the Sun.||No|
|Mercury||Reported for reference|
|Venus||Reported for reference|
|Earth and its other moons||These include Petit's moon, Lilith, Waltemath's moons and Bargby's moons.||Yes|
|Theia (Orpheus)||Alastair G. W. Cameron||Mars-sized impactor that collided with the Earth roughly 4.5 billion years ago; an event which created the Moon. Evidence from 2019 suggests that it may have originated in the outer Solar System or even the Kuiper Belt, and that it is the true source of Earth's water.||No|
|Mars||Reported for reference|
|Planet V||John Chambers, Jack Lissauer||This planet may have been located between Mars and the asteroid belt before the gravity of Jupiter perturbed it so much that its orbit became eccentric. Planet V was ultimately lost, likely crashing into Mars, Jupiter, or into the Sun.||No|
|Phaeton||Heinrich W. M. Olbers, J. D. Titius, Johann, E. Bode||The planet situated between Mars and Jupiter whose destruction supposedly led to the formation of the asteroid belt. This hypothesis is now considered unlikely, since the asteroid belt has far too little mass to have resulted from the explosion of a large planet; however the hypothesis has not been ruled out with recent evidence suggesting it is not the only planet that shattered to form the asteroids.||No|
|Enyo and Bellona||Michael Mark Woolfson||Two super-Earth (or even supergiant) planets theorized by Michael Woolfson as part of his Capture theory on Solar System formation. Originally the Solar System's two innermost planets, these two collided, ejecting Enyo (save its moons Mars, the Moon, Pluto, and the other dwarf planets) out of the Solar System and shattering Bellona to form the Earth, Venus, Mercury, asteroid belt, and comets.||Yes|
|Planets V, K, LHB-A, and LHB-B||Tom Van Flandern||Planet V (not to be confused with Planet V above) and Planet K collided, forming the Asteroid Belt. Mars was once the (captured) moon of Planet V. LHB-A was Jupiter's original twin, which exploded due to tidal forces. Due to being a gas giant it left no trace. LHB-B, Saturn's original twin, suffered the same fate. Their explosions supposedly contributed to the Late Heavy Bombardment.
|Jupiter||Jupiter was heavily responsible for the destruction of most of the hypothetical Solar System bodies.||Reported for reference|
|Saturn and hypothetical moons||William Pickering, Hermann Goldschmidt||
|Fifth giant of the Nice model||Nice model||In the Five-planet Nice model a fifth giant planet originally in an orbit between Saturn and Neptune (which was originally closer to the Sun than Uranus) is ejected from the Solar System into interstellar space after a close encounter with Jupiter, resulting in a rapid divergence of Jupiter's and Saturn's orbit may have ensured the orbital stability of the terrestrial planets in the inner Solar System. It may have also precipitated the Late Heavy Bombardment of the inner Solar System.||No|
|Uranus||Reported for reference|
|Neptune||Reported for reference|
|Pluto||Reported for reference|
|Various planets beyond Neptune||various||
||Italics mean ruled out|