Hypothetical planet
Encyclopedia
A hypothetical Solar System object is a planet
, natural satellite
or similar body in our 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.
Planet
A planet is a celestial body orbiting a star or stellar remnant that is massive enough to be rounded by its own gravity, is not massive enough to cause thermonuclear fusion, and has cleared its neighbouring region of planetesimals.The term planet is ancient, with ties to history, science,...
, natural satellite
Natural satellite
A natural satellite or moon is a celestial body that orbits a planet or smaller body, which is called its primary. The two terms are used synonymously for non-artificial satellites of planets, of dwarf planets, and of minor planets....
or similar body in our Solar System
Solar System
The Solar System consists of the Sun and the astronomical objects gravitationally bound in orbit around it, all of which formed from the collapse of a giant molecular cloud approximately 4.6 billion years ago. The vast majority of the system's mass is in the Sun...
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.
Planets
- Fifth planet (hypothetical)Fifth planet (hypothetical)In the history of astronomy, a handful of solar system bodies have been counted as the fifth planet from the Sun. Under the present definition of a planet, this celestial body is Jupiter.-Previous fifth planets:...
, historical speculation about a planet between the orbits of Mars and Jupiter.- PhaetonPhaeton (hypothetical planet)Phaeton is the name of a hypothetical planet posited to once have existed between the orbits of Mars and Jupiter whose destruction supposedly led to the formation of the asteroid belt...
, a planet situated between the orbits of MarsMarsMars is the fourth planet from the Sun in the Solar System. The planet is named after the Roman god of war, Mars. It is often described as the "Red Planet", as the iron oxide prevalent on its surface gives it a reddish appearance...
and JupiterJupiterJupiter is the fifth planet from the Sun and the largest planet within the Solar System. It is a gas giant with mass one-thousandth that of the Sun but is two and a half times the mass of all the other planets in our Solar System combined. Jupiter is classified as a gas giant along with Saturn,...
whose destruction supposedly led to the formation of the asteroid beltAsteroid beltThe asteroid belt is the region of the Solar System located roughly between the orbits of the planets Mars and Jupiter. It is occupied by numerous irregularly shaped bodies called asteroids or minor planets...
. 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 VPlanet VPlanet V is a hypothetical fifth planet posited by NASA scientists John Chambers and Jack Lissauer to have once existed between Mars and the asteroid belt, based on computer simulations...
, a planet thought by John Chambers and Jack Lissauer to have once existed between MarsMarsMars is the fourth planet from the Sun in the Solar System. The planet is named after the Roman god of war, Mars. It is often described as the "Red Planet", as the iron oxide prevalent on its surface gives it a reddish appearance...
and the asteroid beltAsteroid beltThe asteroid belt is the region of the Solar System located roughly between the orbits of the planets Mars and Jupiter. It is occupied by numerous irregularly shaped bodies called asteroids or minor planets...
, based on computer simulations.
- Phaeton
- Planet XPlanet XFollowing the discovery of the planet Neptune in 1846, there was considerable speculation that another planet might exist beyond its orbit. The search began in the mid-19th century but culminated at the start of the 20th with Percival Lowell's quest for Planet X...
, a hypothetical planet beyond NeptuneNeptuneNeptune is the eighth and farthest planet from the Sun in the Solar System. Named for the Roman god of the sea, it is the fourth-largest planet by diameter and the third largest by mass. Neptune is 17 times the mass of Earth and is slightly more massive than its near-twin Uranus, which is 15 times...
. Initially employed to account for supposed perturbationsPerturbation (astronomy)Perturbation is a term used in astronomy in connection with descriptions of the complex motion of a massive body which is subject to appreciable gravitational effects from more than one other massive body....
(systematic deviations) in the orbits of UranusUranusUranus is the seventh planet from the Sun. It has the third-largest planetary radius and fourth-largest planetary mass in the Solar System. It is named after the ancient Greek deity of the sky Uranus , the father of Cronus and grandfather of Zeus...
and Neptune, it has been disproved to cause any such perturbations, while the belief in them inspired the search for PlutoPlutoPluto, formal designation 134340 Pluto, is the second-most-massive known dwarf planet in the Solar System and the tenth-most-massive body observed directly orbiting the Sun...
. The concept has been re-applied to account for subsequent observations of Kuiper BeltKuiper beltThe Kuiper belt , sometimes called the Edgeworth–Kuiper belt, is a region of the Solar System beyond the planets extending from the orbit of Neptune to approximately 50 AU from the Sun. It is similar to the asteroid belt, although it is far larger—20 times as wide and 20 to 200 times as massive...
objects, however. - Theia, a Mars-sized impactor believed to have collided with the Earth roughly 4.5 billion years ago; an event which created the MoonMoonThe Moon is Earth's only known natural satellite,There are a number of near-Earth asteroids including 3753 Cruithne that are co-orbital with Earth: their orbits bring them close to Earth for periods of time but then alter in the long term . These are quasi-satellites and not true moons. For more...
. - VulcanVulcan (hypothetical planet)Vulcan was a small planet proposed to exist in an orbit between Mercury and the Sun. In an attempt to explain peculiarities of Mercury's orbit, in the 19th-century French mathematician Urbain Jean Joseph Le Verrier hypothesized that they were the result of another planet, which he named Vulcan...
, a hypothetical planet once believed to exist inside the orbit of MercuryMercury (planet)Mercury is the innermost and smallest planet in the Solar System, orbiting the Sun once every 87.969 Earth days. The orbit of Mercury has the highest eccentricity of all the Solar System planets, and it has the smallest axial tilt. It completes three rotations about its axis for every two orbits...
.- Vulcanoids, a ring of asteroids which may exist within a gravitationally stable region inside Mercury's orbit.
- TycheTyche (hypothetical planet)Tyche is the nickname given to a hypothetical gas giant planet located in the Solar System's Oort cloud, first proposed in 1999 by astronomer John Matese of the University of Louisiana at Lafayette. Matese and his colleague Daniel Whitmire argue that evidence of Tyche's existence can be seen in a...
, a hypothetical planet in the Oort CloudOort cloudThe Oort cloud , or the Öpik–Oort cloud , is a hypothesized spherical cloud of comets which may lie roughly 50,000 AU, or nearly a light-year, from the Sun. This places the cloud at nearly a quarter of the distance to Proxima Centauri, the nearest star to the Sun...
supposedly responsible for producing the statistical excess in long period cometCometA comet is an icy small Solar System body that, when close enough to the Sun, displays a visible coma and sometimes also a tail. These phenomena are both due to the effects of solar radiation and the solar wind upon the nucleus of the comet...
s in a band. - A hypothetical fifth gas giantHypothetical fifth gas giantThe fifth gas giant hypothesis is an attempt to explain apparent inconsistencies in the formation of the Solar System. Apart from Jupiter, Saturn, Uranus and Neptune, theorists argue that there was once a fifth gas giant, which was expelled from the Solar System in its formative...
has been mooted in a trans-Saturnian orbit between SaturnSaturnSaturn is the sixth planet from the Sun and the second largest planet in the Solar System, after Jupiter. Saturn is named after the Roman god Saturn, equated to the Greek Cronus , the Babylonian Ninurta and the Hindu Shani. Saturn's astronomical symbol represents the Roman god's sickle.Saturn,...
and UranusUranusUranus is the seventh planet from the Sun. It has the third-largest planetary radius and fourth-largest planetary mass in the Solar System. It is named after the ancient Greek deity of the sky Uranus , the father of Cronus and grandfather of Zeus...
, which was subsequently flung out of the Solar System into interstellar space after a close encounter with JupiterJupiterJupiter is the fifth planet from the Sun and the largest planet within the Solar System. It is a gas giant with mass one-thousandth that of the Sun but is two and a half times the mass of all the other planets in our Solar System combined. Jupiter is classified as a gas giant along with Saturn,...
, resulting in transferred angular momentumAngular momentumIn physics, angular momentum, moment of momentum, or rotational momentum is a conserved vector quantity that can be used to describe the overall state of a physical system...
which caused Jupiter to recede from the Sun and may have insured the orbital stability of the inner terrestrial planets. It may have also precipitated the Late Heavy BombardmentLate Heavy BombardmentThe Late Heavy Bombardment is a period of time approximately 4.1 to 3.8 billion years ago during which a large number of impact craters are believed to have formed on the Moon, and by inference on Earth, Mercury, Venus, and Mars as well...
of the inner Solar System
Moons
- ChironChiron (hypothetical moon)Chiron is the name given to a supposed moon of Saturn sighted by Hermann Goldschmidt in 1861. It has since been determined that no such moon exists....
, a moon of SaturnSaturnSaturn is the sixth planet from the Sun and the second largest planet in the Solar System, after Jupiter. Saturn is named after the Roman god Saturn, equated to the Greek Cronus , the Babylonian Ninurta and the Hindu Shani. Saturn's astronomical symbol represents the Roman god's sickle.Saturn,...
supposedly sighted by Hermann Goldschmidt in 1861 but never observed by anyone else. - Other moons of Earth, such as that thought by Frederic PetitFrédéric Petit (astronomer)Frédéric Petit was a French astronomer. He was the first director of the Toulouse Observatory, located in in Toulouse, France, serving from 1838–1865. In 1846 he announced that he had discovered a second moon of Earth...
, director of the Observatory of Toulouse, to have been observed three times on March 21, 1846. - Mercury's moonMercury's moonA moon orbiting Mercury was, for a short time, believed to exist.On March 27, 1974, two days before Mariner 10 made its flyby of Mercury, instruments began registering large amounts of ultraviolet radiation in the vicinity of Mercury which, according to one astronomer, "had no right to be there"...
, hypothesised to account for a sudden burst of radiation detected by Mariner 10Mariner 10Mariner 10 was an American robotic space probe launched by NASA on November 3, 1973, to fly by the planets Mercury and Venus. It was launched approximately two years after Mariner 9 and was the last spacecraft in the Mariner program...
. It was disproved by the spacecraft's subsequent flyby. An object thought to be orbiting Mercury eventually revealed itself to be the star 31 Crateris. - NeithNeith (hypothetical moon)Neith is the name given to an object first sighted by Giovanni Cassini, which he believed to be a moon of Venus. It has since been determined that no such moon exists.In 1672, Giovanni Cassini found a small object close to Venus...
, a purported moon of VenusVenusVenus is the second planet from the Sun, orbiting it every 224.7 Earth days. The planet is named after Venus, the Roman goddess of love and beauty. After the Moon, it is the brightest natural object in the night sky, reaching an apparent magnitude of −4.6, bright enough to cast shadows...
, 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. - ThemisThemis (hypothetical moon)On April 28, 1905, William H. Pickering, who had seven years earlier discovered Phoebe, announced the discovery of a tenth satellite of Saturn, which he promptly named Themis. The photographic plates on which it supposedly appeared, thirteen in all, spanned a period between April 17 and July 8, 1904...
, a moon of Saturn which astronomer William PickeringWilliam Henry PickeringWilliam Henry Pickering was an American astronomer, brother of Edward Charles Pickering. He was elected a Fellow of the American Academy of Arts and Sciences in 1883.-Work:...
claimed to have discovered in 1905, but which was never seen again. - S/2000 J 11S/2000 J 11S/2000 J 11 was an object believed to be the second-outermost prograde irregular satellite of Jupiter. It was discovered by a team of astronomers from the University of Hawaii led by Scott S. Sheppard in 2000....
was an object reportedly situated in the vicinity of Jupiter, but its orbit was never determined and later searches could not find it. It is no longer considered a likely Jovian satellite.
Star
- NemesisNemesis (star)Nemesis is a hypothetical hard-to-detect red dwarf star, white dwarf star or brown dwarf, originally postulated in 1984 to be orbiting the Sun at a distance of about 95,000 AU , somewhat beyond the Oort cloud, to explain a perceived cycle of mass extinctions in the geological record, which seem to...
, a brown dwarfBrown dwarfBrown dwarfs are sub-stellar objects which are too low in mass to sustain hydrogen-1 fusion reactions in their cores, which is characteristic of stars on the main sequence. Brown dwarfs have fully convective surfaces and interiors, with no chemical differentiation by depth...
/red dwarfRed dwarfAccording to the Hertzsprung-Russell diagram, a red dwarf star is a small and relatively cool star, of the main sequence, either late K or M spectral type....
whose existence was suggested in 1984 by physicist Richard A. MullerRichard A. MullerRichard A. Muller is a noted American professor of physics at the University of California, Berkeley. He is also a faculty senior scientist at the Lawrence Berkeley National Laboratory.-Career:...
, based on purported periodicities in mass extinctions within Earth's fossil record. Its regular passage through the Solar System's Oort cloudOort cloudThe Oort cloud , or the Öpik–Oort cloud , is a hypothesized spherical cloud of comets which may lie roughly 50,000 AU, or nearly a light-year, from the Sun. This places the cloud at nearly a quarter of the distance to Proxima Centauri, the nearest star to the Sun...
would send large numbers of comets towards Earth, massively increasing the chances of an impact.
See also
- Hypothetical fifth gas giantHypothetical fifth gas giantThe fifth gas giant hypothesis is an attempt to explain apparent inconsistencies in the formation of the Solar System. Apart from Jupiter, Saturn, Uranus and Neptune, theorists argue that there was once a fifth gas giant, which was expelled from the Solar System in its formative...
- Planet formation
- Theoretical planetologyTheoretical planetologyTheoretical planetology, also known as theoretical planetary science is a branch of planetary sciences that developed in the 20th century.- Nature of the work :...
- Oort cloudOort cloudThe Oort cloud , or the Öpik–Oort cloud , is a hypothesized spherical cloud of comets which may lie roughly 50,000 AU, or nearly a light-year, from the Sun. This places the cloud at nearly a quarter of the distance to Proxima Centauri, the nearest star to the Sun...
- Planets beyond NeptunePlanets beyond NeptuneFollowing the discovery of the planet Neptune in 1846, there was considerable speculation that another planet might exist beyond its orbit. The search began in the mid-19th century but culminated at the start of the 20th with Percival Lowell's quest for Planet X...
- Tenth planet (disambiguation)
- Ninth planet (disambiguation)
- Trans-Neptunian objectTrans-Neptunian objectA trans-Neptunian object is any minor planet in the Solar System that orbits the Sun at a greater distance on average than Neptune.The first trans-Neptunian object to be discovered was Pluto in 1930...
- Trans-Neptunian objects in fictionTrans-Neptunian objects in fictionThe region of the Solar System beyond Neptune contains sparse populations of small icy objects. These include the Kuiper belt, with its well-known member Pluto, and other plutoids including Haumea and Makemake...