List of hypothetical Solar System objects

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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.

List

The following is a list of hypothetical Solar System bodies in order of their distance and order from the Sun.

List of hypothetical Solar System bodies
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.[1] 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.[2] 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.[3] 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.[4] 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.[5][6] 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.


One major argument against exploding planets and moons is that there would not be an energy source powerful enough to cause such explosions.

Yes
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
  • Themis, a moon of Saturn which astronomer William Pickering claimed to have discovered in 1905, but which was never seen again.[7]
  • Chiron, a moon of Saturn supposedly sighted by Hermann Goldschmidt in 1861 but never observed by anyone else.
Yes
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.[8] No
Uranus Reported for reference
Neptune Reported for reference
Pluto Reported for reference
Various planets beyond Neptune various


Various planets beyond Neptune:

  • Planet Nine, a planet proposed to explain apparent alignments in the orbits of a number of distant trans-Neptunian objects.
  • Planet X, a hypothetical planet beyond Neptune. Initially employed to account for supposed perturbations (systematic deviations) in the orbits of Uranus and Neptune, belief in its existence ultimately inspired the search for Pluto. Though the concept has since been abandoned following more precise measurements of Neptune's mass, which accounted for all observed perturbations, it has been re-applied to account for supposed deviations in the motions of Kuiper belt objects. Such explanations are still controversial, however.
  • Tom Van Flandern's Planets T and X, which exploded and left no trace.
  • Hyperion
  • Tyche, a hypothetical planet in the Oort Cloud supposedly responsible for producing the statistical excess in long period comets in a band. Results from the WISE telescope survey in 2014 have ruled it out.
  • Oceanus and two more planets, proposed by Thomas Jefferson Jackson See.
  • Brahma and Vishnu, proposed by Venkatesh P. Ketakar.
  • Hades, proposed by Theodor Grigull
  • "Planet Ten" as proposed by Volk and Malhotra, a Mars-sized planetoid believed to be responsible for the inclination of Kuiper Belt objects beyond the Kuiper cliff at 50 AU
  • "Planet Ten" as proposed by Sverre Aarseth and Carlos and Raúl de la Fuente Marcos, which they believe stabilizes the orbits of other Kuiper Belt objects
  • Oreon and Terminus, which fragmented to form the Kuiper Belt.
  • Planets O, P, Q, R, S, T, and U, proposed by William Henry Pickering
  • A Trans-Plutonian planet proposed by Tadashi Mukai and Patryk Sofia Lykawka, roughly the size of Earth or Mars with an eccentric orbit between 100 to 200 AU
  • Another Trans-Neptunian planet at 1,500 AU away from the Sun, proposed by Rodney Gomes in 2012
Italics mean ruled out

References