List of hypothetical Solar System objects

• Counter-Earth, a planet situated on the other side of the Sun from that of the Earth.
• Fifth planet (hypothetical), historical speculation about a planet between the orbits of Mars and Jupiter.
• Phaeton, a planet situated between the orbits of 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. 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.{{Cite web|url=http://news.ufl.edu/articles/2018/06/study-reveals-secret-origins-of-asteroids-and-meteorites.php|title=Study reveals secret origins of asteroids and meteorites|date=2018-07-02|website=news.ufl.edu|language=en|access-date=2018-10-17}}
• Krypton, named after the destroyed native world of Superman, theorized by Michael 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{{cite journal |author=Ovenden, M.W. |year=1972 |title=Bode's law and the missing planet |journal=Nature |volume=239 |pages=508–509|doi=10.1038/239508a0 |s2cid=30520852 }}{{cite book |author=Ovenden, M.W. |year=1973 |chapter=Planetary Distances and the Missing Planet |pages=319–332 |title=Recent Advances in Dynamic Astronomy |publisher=Reidel}}{{full citation needed|date=July 2019}}
• 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.
• 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. The concept has since been abandoned following more precise measurements of Neptune's mass, which accounted for all observed perturbations.
• Hyperion, a planet hypothesized in 1848 by Jacques Babinet.
• "Planet Ten", a large distant 10th planet theorized in 2000 to have had an effect on Kuiper Belt formation.{{Cite journal|last1=Collander-Brown|first1=S.|last2=Maran|first2=M.|last3=Williams|first3=I. P.|date=2000-10-11|title=The effect on the Edgeworth-Kuiper Belt of a large distant tenth planet|journal=Monthly Notices of the Royal Astronomical Society|language=en|volume=318|issue=1|pages=101–108|doi=10.1046/j.1365-8711.2000.03640.x|bibcode=2000MNRAS.318..101C|issn=0035-8711|doi-access=free}}
• Tyche, a hypothetical planet in the Oort Cloud supposedly responsible for producing the statistical excess in long period comets in a band.The Independent, [https://www.independent.co.uk/news/science/up-telescope-search-begins-for-giant-new-planet-2213119.html "Up telescope! Search begins for giant new planet"], Sunday 13 February 2011, Paul Rodgers Results from the WISE telescope survey in 2014 have ruled it out.{{cite journal

|journal=The Astrophysical Journal

|last=K. L. |first=Luhman

|title=A Search For A Distant Companion To The Sun With The Wide-field Infrared Survey Explorer

|url=http://iopscience.iop.org/0004-637X/781/1/4?fromSearchPage=true

|date=7 March 2014

|volume=781

|pages=4 |number=1

|doi=10.1088/0004-637X/781/1/4

|access-date=20 March 2014 |bibcode = 2014ApJ...781....4L |s2cid=122930471 |url-access=subscription

}}{{Cite journal | title=Persistent evidence of a jovian mass solar companion in the Oort cloud | last1=Matese|first1=John J.|last2=Whitmire|first2=Daniel P.| journal=Icarus | year=2011 | volume=211 | issue=2 | pages=926–938 | doi=10.1016/j.icarus.2010.11.009|arxiv=1004.4584 | bibcode=2011Icar..211..926M| s2cid=44204219}}{{cite news|last=Helhoski|first=Anna|title=News 02/16/11 Does the Solar System Have Giant New Planet?|url=http://norwalk.dailyvoice.com/news/does-solar-system-have-giant-new-planet|access-date=10 July 2012|newspaper=The Norwalk Daily Voice}}

• Up to three planets at 42 (named Oceanus), 56, and 72 AU (both unnamed) from the sun respectively, proposed by Thomas Jefferson Jackson See in 1909.{{cite journal|title=A Career of Controversy: The Anomaly of T. J. J. See|author=TJ Sherrill|pages=25–50|date=1999|bibcode= 1999JHA....30...25S|journal=Journal for the History of Astronomy|volume=30|doi=10.1177/002182869903000102|s2cid=117727302}}
• Brahma and Vishnu, proposed by Venkatesh P. Ketakar.{{cite journal|title=Prediction of Pluto by V. P. Ketakar|author1=JG Chhabra|author2=SD Sharma|author3=M Khanna|journal=Indian Journal of History of Science|date=1984|volume=19|issue=1|pages=18–26|url=http://www.new.dli.ernet.in/rawdataupload/upload/insa/INSA_1/20005abd_18.pdf|access-date=2008-09-04|bibcode=1984InJHS..19...18C|url-status=dead|archive-url=https://web.archive.org/web/20090225135119/http://www.new.dli.ernet.in/rawdataupload/upload/insa/INSA_1/20005abd_18.pdf|archive-date=2009-02-25}}
• Hades, proposed by Theodor Grigull{{when|date=August 2020}}{{Cite web | url=https://archive.org/stream/galaxymagazine-1956-08#page/n87/mode/2up |title = Galaxy Magazine (August 1956)|date = August 1956}}
• "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{{cite news |last=Osbourne |first=Hannah |title=Forget Planet 9 - There's Evidence Of A Tenth Planet Lurking At The Edge Of The Solar System |url=http://www.newsweek.com/planet-10-lurking-edge-solar-system-628517 |date=23 June 2017 |work=Newsweek |access-date=23 June 2017 }}{{cite journal |last1=Volk |first1=Kathryn |last2=Malhotra |first2=Renu |title=The curiously warped mean plane of the Kuiper belt |arxiv=1704.02444 |doi=10.3847/1538-3881/aa79ff |volume=154 |issue=2 |journal=The Astronomical Journal |page=62|bibcode = 2017AJ....154...62V |year=2017|s2cid=5756310 |doi-access=free }}
• "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{{Cite news | url=https://www.telegraph.co.uk/science/2016/06/13/solar-system-may-hold-ten-planets-or-more-say-scientists/ |title = Solar System may hold ten planets or more, say scientists|newspaper = The Telegraph|date = 13 June 2016|last1 = Knapton|first1 = Sarah}}{{Cite journal |doi = 10.1038/nature13156|title = A Sedna-like body with a perihelion of 80 astronomical units|year = 2014|last1 = Trujillo|first1 = Chadwick A.|last2 = Sheppard|first2 = Scott S.|journal = Nature|volume = 507|issue = 7493|pages = 471–474|pmid = 24670765|bibcode = 2014Natur.507..471T|s2cid = 4393431}}
• Planets O, P, Q, R, S, T, and U, proposed by William Henry Pickering{{Cite journal |doi = 10.1086/351668|title = W. H. Pickering's Planetary Predictions and the Discovery of Pluto|year = 1976|last1 = Hoyt|first1 = William Graves|journal = Isis|volume = 67|issue = 4|pages = 551–564|pmid = 794024|s2cid = 26512655}}
• A Trans-Plutonian planet proposed by Tadashi Mukai and Patryk Sofia Lykawka{{when|date=December 2024|reason=date missing, there is a reference where the planet is proposed dating to 2008}}, roughly the size of Earth or Mars with an eccentric orbit between 100 and 200 AU{{cite journal |last1=Patryk S. |first1=Lykawka |last2=Tadashi |first2=Mukai |year=2008 |title=An Outer Planet Beyond Pluto and the Origin of the Trans-Neptunian Belt Architecture |journal=The Astronomical Journal |volume=135 |issue=4 |pages=1161–1200 |arxiv=0712.2198 |bibcode=2008AJ....135.1161L |doi=10.1088/0004-6256/135/4/1161|s2cid=118414447 }}{{cite web |last=Than |first=Ker |date=18 June 2008 |title=Large 'Planet X' May Lurk Beyond Pluto |url=http://www.space.com/5526-large-planet-lurk-pluto.html |website=Space.com |access-date=18 July 2016}}{{cite web |last=Hasegawa |first=Kyoko |date=28 February 2008 |title=Japanese scientists eye mysterious 'Planet X' |url=http://www.bibliotecapleyades.net/hercolobus/esp_hercolobus_66.htm |website=BibliotecaPleyades.net |access-date=18 July 2016}}
• Another Trans-Neptunian planet at 1,500 AU away from the Sun, proposed by Rodney Gomes in 2012{{cite magazine|title=New planet found in our Solar System?|magazine=National Geographic|url=http://news.nationalgeographic.com/news/2012/05/120511-new-planet-solar-system-kuiper-belt-space-science|archive-url=https://web.archive.org/web/20120514021638/http://news.nationalgeographic.com/news/2012/05/120511-new-planet-solar-system-kuiper-belt-space-science/|url-status=dead|archive-date=May 14, 2012|date=2012|access-date=2012-05-21}}
• Theia or Orpheus,{{cite book|last1=Byrne|first1=Charles|title=The Far Side of the Moon: A Photographic Guide|date=2007|publisher=Springer|isbn=9780387732060|page=202|url=https://books.google.com/books?id=Wm7fspWpJBAC&pg=PT177}} a Mars-sized impactor believed to have 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.{{Cite journal|last1=Budde|first1=Gerrit|last2=Burkhardt|first2=Christoph|last3=Kleine|first3=Thorsten|date=2019-05-20|title=Molybdenum isotopic evidence for the late accretion of outer Solar System material to Earth|url=http://www.nature.com/articles/s41550-019-0779-y|journal=Nature Astronomy|volume=3|issue=8|pages=736–741|language=en|doi=10.1038/s41550-019-0779-y|bibcode=2019NatAs...3..736B|s2cid=181460133|issn=2397-3366|url-access=subscription}}
• Vulcan, a hypothetical planet once 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.
• 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.{{cite news| last = Alexander| first = Amir| title = Small, Faint, and Elusive: The Search for Vulcanoids| publisher = The Planetary Society| date = 2004| url = http://www.planetary.org/news/2004/0202_Small_Faint_and_Elusive_The_Search.html| access-date = 2008-12-25| url-status = dead| archive-url = https://web.archive.org/web/20081011231437/http://www.planetary.org/news/2004/0202_Small_Faint_and_Elusive_The_Search.html| archive-date = 2008-10-11}} None have been detected by STEREO or SOHO.{{cite journal

|last=Steffl |first=A. J.

|author2=Cunningham, N. J. |author3=Shinn, A. B. |author4= Stern, S. A.

|title=A Search for Vulcanoids with the STEREO Heliospheric Imager

|journal=Icarus

|volume=233 |issue=1 |pages=48–56 |date=2013

|doi=10.1016/j.icarus.2012.11.031

|arxiv=1301.3804

|bibcode= 2013Icar..223...48S|s2cid=118612132

}}{{Cite journal| last1 = Schumacher| first1 = G.| last2 = Gay | first2 = J.| title = An Attempt to detect Vulcanoids with SOHO/LASCO images | journal = Astronomy & Astrophysics | volume = 368| issue = 3 | pages = 1108–1114 | date = 2001 | doi = 10.1051/0004-6361:20000356 | bibcode=2001A&A...368.1108S| doi-access = free}}

• 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.{{Cite web | url=https://phys.org/news/2016-04-sun-eaten-super-earth-breakfast.html | title=Our sun may have eaten a super-Earth for breakfast}}
• The Fifth Giant is a hypothetical fifth giant planet originally in an orbit between Saturn and Uranus but was 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 which 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.Lisa Grossman: "Lost planet explains solar system puzzle" New Scientist: 01.10.2011: 14–15 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 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 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.{{Cite journal | doi=10.1093/mnras/180.2.243| title=Interactions in the early solar system| year=1977| last1=Dormand| first1=J. R.| last2=Woolfson| first2=M. M.| journal=Monthly Notices of the Royal Astronomical Society| volume=180| issue=2| pages=243–279| bibcode=1977MNRAS.180..243D| doi-access=free}}
• A captured planet from another solar system was proposed to exist in the Oort cloud much further than the hypothetical Planet Nine.{{cite web | url=https://www.popsci.com/science/planet-solar-system-oort-cloud/ | title=There might be an ice giant planet hiding in our solar system | date=27 June 2023 }}{{Cite journal |arxiv=2306.11109 |doi=10.1093/mnrasl/slad079 |title=Oort cloud (Exo)planets |date=2023 |last1=Raymond |first1=Sean N. |last2=Izidoro |first2=Andre |last3=Kaib |first3=Nathan A. |journal=Monthly Notices of the Royal Astronomical Society: Letters |volume=524 |pages=L72–L77 |doi-access=free }}

• Chiron, a moon of Saturn supposedly sighted by Hermann Goldschmidt in 1861 but never observed by anyone else.
• Chrysalis, a hypothetical moon of Saturn, named in 2022 by scientists of the Massachusetts Institute of Technology using data from the Cassini–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 the rings of Saturn.
• Other moons of Earth, such as Petit's moon, Lilith, Waltemath's moons and Bagby's moons.
• Mercury's moon, hypothesised to account for an unusual pattern of radiation detected by Mariner 10 in the vicinity of Mercury. Subsequent data from the mission revealed the actual source 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 and internal reflections inside the optics of particular telescope designs. It was also alternatively proposed by Jean-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 astronomer William Pickering claimed to have discovered in 1905, but which was never observed again.[http://www.nineplanets.org/hypo.html#sat Hypothetical Planets]

• Nemesis, a brown or red dwarf whose existence was suggested in 1984 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. Also believed to be the cause of minor planet Sedna's unusual elongated orbit. The existence of the Nemesis in the modern Solar system was ruled out in 2014 after the infrared survey performed by WISE spacecraft found no brown dwarf up to {{convert|10000|au|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.Williams, 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
• 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.
• One assumption suggests that the hypothetical Planet Nine is actually a primordial black hole.{{Cite web|url=https://astronomy.com/news/2019/10/planet-nine-may-be-a-black-hole-the-size-of-a-baseball|title = Planet Nine may be a black hole the size of a baseball| date=October 2019 }}

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• Subsatellite
• Oort cloud
• Planets beyond Neptune
• Nebular hypothesis
• Tenth planet (disambiguation)
• Theoretical planetology
• Trans-Neptunian object
• Trans-Neptunian objects in fiction

{{div col end}}

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