Hypothetical planetary object

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This article is about hypothetical planetary objects in astronomy. For hypothetical planetary objects not recognised by science, see Hypothetical planetary object (non-scientific).

A hypothetical planetary object is a planet, natural satellite or similar body 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.

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[edit] Hypothetical planets in our solar system

Our solar system is by no means fully mapped and charted. Much of its territory is still unknown, and many astronomers have hypothesized from indirect observation that other substantial objects could still exist undetected in its farthest reaches.

[edit] Vulcan/Vulcanoids

Main articles: Vulcan (hypothetical planet) and Vulcanoid asteroid

In the 19th century, the astronomer Urbain Le Verrier, credited with the discovery of Neptune, attempted to locate a hypothetical planet within the orbit of Mercury that he believed was causing perturbations in its orbit. This planet, which he named Vulcan after the Roman god of the forge due to its closeness to the Sun, was never observed, and Einstein's general relativity theory subsequently resolved the issue of Mercury's orbit.[1]

However, a gravitationally stable region does exist between Mercury and the Sun, and some astronomers, notably Alan Stern, contend that a field of small minor planets, the Vulcanoids, should exist within it. However repeated observations of the region have yet to yield any results, and the Vulcanoids, if they exist, must be rather small and few in number.[2] Some conclude that the existence of the Vulcanoids is impossible, as any minor planet within the orbit of Mercury would eventually be destabilised by the Yarkovsky effect; motion by the force of its own heat.[3]

While no objects orbiting entirely within Mercury's orbit have been discovered, over 850 Kreutz Sungrazers have been discovered using the Solar and Heliospheric Observatory, all of which have a perihelion well inside Mercury's orbit.[4]

[edit] Planet X

Main article: Planet X
See also: Hypothetical trans-Neptunian planets

In the early 20th century, astronomer Percival Lowell's observation of apparent irregularities in the orbits of Uranus and Neptune led him to conclude that a distant planet, which he called Planet X, must lie beyond them. The Lowell Observatory's long search for this planet ultimately led to the discovery of Pluto. However, Pluto's mass was found to be too small to disturb the other planets' orbits significantly, and subsequent measurements by the Voyager 2 spacecraft showed that earlier calculations of Neptune's mass had been in error, leading to the irregularities observed.[5] Today, few scientists accept Lowell's theory; however, a number of recent observations have reopened the debate on the existence of a "Planet X", even if it would bear little resemblance to that envisioned by Lowell.

  • The Kuiper belt has a very sharply defined edge. At around 49 AU, a sharp dropoff occurs in the number of objects observed. This dropoff is known as the "Kuiper Cliff", and as yet its cause is unknown. Some speculate that something must exist beyond the belt large enough to sweep up the remaining debris, perhaps as large as Earth or Mars. This view is still controversial, however.[6]
  • Dr. John Murray of the Open University and John Matese of the University of Louisiana at Lafayette believe that the motions of long-term comets in the sky suggest the existence of a large, distant planet, or, more likely, a small substellar companion such as a Brown dwarf, in the deep solar system. This hypothetical substellar object is not Nemesis, since its existence is inferred from a different set of data; however there is the possibility that both sets of data could be true for the same object.[7]

[edit] Nemesis

Main article: Nemesis (star)

Physicist Richard A. Muller has hypothesised that the Sun may be part of a binary star system, with a distant companion named Nemesis. Nemesis was proposed to explain some timing regularities of the great extinctions of life on Earth. The hypothesis says that Nemesis creates periodical perturbations in the Oort cloud of comets surrounding the solar system, causing a "comet shower". Some of them hit Earth, causing destruction of life. This hypothesis is no longer taken seriously by most scientists, mostly because infrared surveys failed to spot any such object, which should have been very conspicuous at those wavelengths.[8]

[edit] Theia

Main article: Giant impact hypothesis

A onetime Trojan to the Earth that, once its size grew to roughly that of Mars, became unstable in its orbit and collided with the Earth, transforming its crust and upper mantle into a magma ocean, and ejecting massive amounts of light material into orbit, which eventually coalesced into the Moon. This theory is known as the giant impact hypothesis.[9]

[edit] Planets between Mars and Jupiter

Main article: Fifth planet (hypothetical)

[edit] Phaeton

Main article: Phaeton (hypothetical planet)

A planet situated between the orbits of Mars and Jupiter whose destruction supposedly led to the formation of asteroids and meteorites. One of the first who believed that asteroids are the result of an exploded planet was German astronomer Wilhelm Olbers (1758–1840). The name "Phaeton" for this planet was chosen by the Russian scientist, E. L. Krinov. Nowadays this hypothesis is disregarded by the main scientific community.[citation needed]

[edit] Planet V

Main article: Planet V

Planet V is a hypothetical planet thought by NASA space scientists John Chambers and Jack Lissauer to have once existed between Mars and the asteroid belt, based on computer simulations. The computer modeling findings of Chambers and Lissauer were presented during the 33rd Lunar and Planetary Science Conference, held March 11 through 15, 2002, and sponsored by NASA and the Lunar and Planetary Institute.[10]

[edit] Hypothetical moons

[edit] Mercury's moon

Main article: Mercury's moon

A moon hypothesised to account for a sudden burst of radiation detected by Mariner 10. Disproved by the spacecraft's subsequent flyby. An object thought to be orbiting Mercury eventually revealed itself to be the star 31 Crateris.

[edit] Neith

Main article: Neith (hypothetical moon)

A purported moon of Venus, falsely detected by a number of telescopic observers in the 17th and 18 centuries. Now known not to exist, the object has been explained as a series of misidentified stars.

[edit] Chiron

Main article: Chiron (hypothetical moon)

A moon of Saturn supposedly sighted by Hermann Goldschmidt in 1861 but never observed by anyone else.

[edit] Themis

Main article: Themis (hypothetical moon)

A moon of Saturn which astronomer William Pickering claimed to have discovered in 1905, but which was never seen again.[11]

[edit] Hypothetical extrasolar planets

Main article: List of unconfirmed exoplanets

[edit] See also

[edit] References

  1. ^ Paul Schlyter. Hypothetical planets. saaf.se. Retrieved on 2006-07-23.
  2. ^ Durda D.D.; Stern S.A.; Colwell W.B.; Parker J.W.; Levison H.F.; Hassler D.M. (2004). A New Observational Search for Vulcanoids in SOHO/LASCO Coronagraph Images. Retrieved on 2006-07-23.
  3. ^ Vokrouhlický, David; Farinella, Paolo; Bottke, William F. (2000). The Depletion of the Putative Vulcanoid Population via the Yarkovsky Effect. NASA Smithsonian. Retrieved on 2006-06-25.
  4. ^ NASA - History's Greatest Comet Hunter Discovers 1,000th Comet
  5. ^ Croswell, Ken (1997). Planet Quest: The Epic Discovery of Alien Solar Systems. Oxford University Press p. 66 (ISBN 0-19-288083-7). 
  6. ^ Michael Brooks (2005). 13 Things That Don't Make Sense. NewScientistSpace. Retrieved on 2006-06-23.
  7. ^ Cometary evidence of a massive body in the outer Oort cloud. The University of Louisiana at Lafayette. Retrieved on 2006-07-22.
  8. ^ J. G. Hills (1984). Dynamical constraints on the mass and perihelion distance of Nemesis and the stability of its orbit. Nature. Retrieved on 2006-06-23.
  9. ^ HF-W Chronometry and Inner Solar System Accretion Rates. TDepartment of Earth Sciences, Institute for Isotope Geology and Mineral Resources, ETH Zentrum. Retrieved on 2006-07-22.
  10. ^ A NEW DYNAMICAL MODEL FOR THE LUNAR LATE HEAVY BOMBARDMENT. Chambers and Lissauer, NASA Ames. Retrieved on 2006-11-09.
  11. ^ Hypothetical Planets