Ahypothetical Solar System object is aplanet,natural satellite,subsatellite or similar body in theSolar 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.
Phaeton, a planet situated between the orbits ofMars andJupiter whose destruction supposedly led to the formation of theasteroid 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. In 2018, a study from researchers at the University of Florida found the asteroid belt was created from the fragments of at least five or six ancient planetary-sized objects instead of a single planet.[1]
Krypton, named afterthe destroyed native world ofSuperman, theorized byMichael Ovenden to have been a gas giant between Mars and Jupiter nearly as large as Saturn and also attributed for the formation of the asteroid belt[2][3]
Planet X, a hypothetical planet beyondNeptune. Initially employed to account for supposedperturbations (systematic deviations) in the orbits ofUranus and Neptune, belief in its existence ultimately inspired the search forPluto. The concept has since been abandoned following more precise measurements of Neptune's mass, which accounted for all observed perturbations.
"Planet Ten", a large distant 10th planet theorized in 2000 to have had an effect onKuiper Belt formation.[4]
Tyche, a hypothetical planet in theOort Cloud supposedly responsible for producing the statistical excess in long periodcomets in a band.[5] Results from theWISE telescope survey in 2014 have ruled it out.[6][7][8]
Up to three planets at 42 (named Oceanus), 56, and 72 AU (both unnamed) from the sun respectively, proposed byThomas Jefferson Jackson See in 1909.[9]
Brahma and Vishnu, proposed by Venkatesh P. Ketakar.[10]
"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[12][13]
"Planet Ten" as proposed bySverre Aarseth and Carlos and Raúl de la Fuente Marcos, which they believe stabilizes the orbits of other Kuiper Belt objects[14][15]
A Trans-Plutonian planet proposed by Tadashi Mukai and Patryk Sofia Lykawka[when?], roughly the size of Earth or Mars with an eccentric orbit between 100 and 200 AU[17][18][19]
Another Trans-Neptunian planet at 1,500 AU away from the Sun, proposed by Rodney Gomes in 2012[20]
Theia or Orpheus,[21] a Mars-sized impactor believed to have collided with the Earth roughly 4.5 billion years ago; an event which created theMoon. Evidence from 2019 suggests that it may have originated in the outer Solar System.[22]
Vulcan, a hypothetical planet once believed to exist inside the orbit ofMercury. 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'sGeneral Theory of Relativity.
Vulcanoids, asteroids that may exist within a gravitationally stable region inside Mercury's orbit. 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.[23] None have been detected bySTEREO orSOHO.[24][25]
The lack of vulcanoids led to a suggestion in 2016 that asuper-Earth planet that once orbited the Sun closer to Mercury was able toclear its neighborhood before spiraling down into the Sun.[26]
TheFifth Giant is a hypothetical fifth giant planet originally in an orbit betweenSaturn andUranus but was ejected from the Solar System into interstellar space after a close encounter withJupiter, resulting in a rapid divergence of Jupiter's and Saturn's orbit which may have ensured the orbital stability of theterrestrial planets in the inner Solar System. It may have also precipitated theLate Heavy Bombardment of the inner Solar System.[27] The Fifth Giant may be the hypothetical Planet Nine, remaining captured due to either the gravity of a nearby star or drag from the gaseous remnants of the Solar nebula which reduced the eccentricity of its orbit.
A and B, two super-Earth (or evensupergiant) planets theorized byMichael Woolfson as part of hisCapture theory on Solar System formation. Originally the Solar System's two innermost planets, these two collided, ejecting A (save its moons Mars, the Moon, Pluto, and the other dwarf planets) out of the Solar System and shattering B to form the Earth, Venus, Mercury, asteroid belt, and comets.[28]
A captured planet from another solar system was proposed to exist in the Oort cloud much further than the hypothetical Planet Nine.[29][30]
Chrysalis, a hypothetical moon of Saturn, named in 2022 by scientists of theMassachusetts Institute of Technology using data from theCassini–Huygens mission, thought to have been torn apart by Saturn's tidal forces, somewhere between 200 and 100 million years ago, with up to 99% of its mass being swallowed by Saturn, and the remaining 1% forming therings of Saturn.
Mercury's moon, hypothesised to account for an unusual pattern of radiation detected byMariner 10 in the vicinity ofMercury. Subsequent data from the mission revealed the actual source to be the star31 Crateris.
Neith, a purported moon ofVenus, 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 and internal reflections inside the optics of particular telescope designs. It was also alternatively proposed byJean-Charles Houzeau to be a heliocentric planet that orbited the Sun every 283 days and be in conjunction with Venus every 1080 days.
Themis, a moon of Saturn which astronomerWilliam Pickering claimed to have discovered in 1905, but which was never observed again.[31]
Nemesis, abrown orred dwarf whose existence was suggested in 1984 by physicistRichard A. Muller, based on purported periodicities inmass extinctions within Earth's fossil record. Its regular passage through the Solar System'sOort cloud would send large numbers of comets towards Earth, massively increasing the chances of an impact. Also believed to be the cause of minor planetSedna's unusual elongated orbit. The existence of theNemesis in the modern Solar system was ruled out in 2014 after the infrared survey performed byWISE spacecraft found nobrown dwarf up to 10,000 astronomical units (0.16 ly) from Sun.
Raymond Arthur Lyttleton's model on the formation of the Solar System had a former binary star system by the Sun, which merged and broke into two due to rotational instability, forming Jupiter and Saturn.[32]
Fred Hoyle's model on Solar System formation had a former and more massive binary companion to the Sun that exploded in a supernova due to nuclear fusion failing within its interior and it collapsing as a result (which had not yet been verified at the time). The star's supernova remnant would be captured by the Sun and shaped into a protoplanetary disk, from which the planets formed.[32]
^abWilliams, I.O., Cremin, A.W. 1968. A survey of theories relating to the origin of the solar system. Qtly. Rev. RAS 9: 40–62. ads.abs.harvard.edu/abs
