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Tyche (hypothetical planet)

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Tyche (hypothetical planet)

An artist's rendering of the Oort cloud and the Kuiper belt (inset)

Tyche is the nickname given to a hypothetical gas giant located in the Solar System's Oort cloud, first proposed in 1999 by astrophysicists John Matese, Patrick Whitman and Daniel Whitmire of the University of Louisiana at Lafayette.[1][2] They argue that evidence of Tyche's existence can be seen in a supposed bias in the points of origin for long-period comets. More recently Matese[3] and Whitmire[4] re-evaluated the comet data and noted that Tyche, if it exists, would be detectable in the archive of data that was collected by NASA's Wide-field Infrared Survey Explorer (WISE) telescope.[5] However, in 2014, NASA announced that the WISE survey had ruled out any object as they had defined it.[6][7][8]

History

Matese, Whitmire and their colleague Patrick Whitman first proposed the existence of this planet in 1999,[9] based on observations of the orbits of long-period comets. Most astronomers agree that long-period comets (those with orbits of thousands to millions of years) have a roughly isotropic distribution; that is, they arrive at random from every point in the sky.[10] Because comets are volatile and dissipate over time, astronomers suspect that they must be held in a spherical cloud tens of thousands of AU distant (known as the Oort cloud) for most of their existence.[10] However, Matese and Whitmire claimed that rather than arriving from random points across the sky as is commonly thought, comet orbits were in fact clustered in a band inclined to the orbital plane of the planets. Such clustering could be explained if they were disturbed by an unseen object at least as large as Jupiter, possibly a brown dwarf, located in the outer part of the Oort cloud.[11][12] They also suggested that such an object might explain the trans-Neptunian object Sedna's peculiar orbit.[13] However, the sample size of Oort comets was small and the results were inconclusive.[14]

Orbit

Whitmire and Matese speculate that Tyche's orbit would lie at approximately 500 times Neptune's distance; equivalent to 15,000 AU (2.2×1012 km) from the Sun, a little less than one quarter of a light year. This is still well within the Oort cloud, whose boundary is estimated to be beyond 50,000 AU. It would have an orbital period of roughly 1.8 million years.[15] A failed search of older IRAS data suggests that an object of 5 MJ would need to have a distance greater than 10,000 AU.[7] Such a planet would orbit in a different plane in orientation to our current planet orbits,[16] and probably formed in a wide-binary orbit.[7] Wide binaries may form through capture during the dissolution of a star's birth cluster.[7]

Mass

General size comparison between the Sun, a low-mass star, a brown dwarf, and the planets Jupiter and Earth.

In 2011, Whitmire and Matese speculated that the hypothesized planet could be up to four times the mass of Jupiter and have a relatively high temperature of approximately 200 K[7] (−73°C), due to residual heat from its formation and Kelvin–Helmholtz heating.[17] It would be insufficiently massive to undergo nuclear fusion reactions in its interior, a process which occurs in objects above roughly 13 Jupiter masses. Although more massive than Jupiter, Tyche would be about Jupiter's size since degenerate pressure causes massive gas giants to increase only in density, not in size, relative to their mass. If Tyche was to be found, it was expected to be found by the end of 2013 and only be 1–2 Jupiter masses.[18]

Origin of name

Tyche (Τύχη, meaning "fortune" or "luck" in Greek) was the Greek goddess of fortune and prosperity. The name was chosen to avoid confusion with an earlier similar hypothesis that the Sun has a dim companion named Nemesis, whose gravity triggers influxes of comets into the inner Solar System, leading to mass-extinctions on Earth. Tyche was the name of the "good sister" of Nemesis.[7] This name was first used for an outer Oort cloud object by Davy Kirpatrick at the Infrared Processing and Analysis Center of the California Institute of Technology.[19]

WISE mission

The Wide-field Infrared Survey Explorer (WISE) space telescope has completed an all-sky infrared survey that includes areas where Whitmire and Matese anticipate that Tyche may be found.[7] On March 14, 2012, the first-pass all-sky survey catalog of the WISE mission was released.[20] The co-added (AllWISE) post-cryo second survey of the sky should be released by the end of 2013.[21] On 7 March 2014, NASA reported that the WISE telescope had ruled out the possibility of a Saturn-sized object at 10,000 AU, and a Jupiter-sized or larger object out to 26,000 AU (0.4 light-years).[6][22]

See also

Notes

References

  1. ^ Rodgers, Paul (February 13, 2011). "Up telescope! Search begins for giant new planet".  
  2. ^ Wolchover, Natalie (February 15, 2011). "Article: Astronomers Doubt Giant Planet 'Tyche' Exists in Our Solar System".  
  3. ^ "Astrophysics Homepage of John J. Matese". Ucs.louisiana.edu. 2011-09-21. Retrieved 2013-04-01. 
  4. ^ "Daniel P. Whitmire". Ucs.louisiana.edu. Retrieved 2013-04-01. 
  5. ^ Whitney Clavin (2011-02-18). "Can WISE Find the Hypothetical 'Tyche'?". NASA/JPL. Retrieved 2011-02-19. 
  6. ^ a b K. L., Luhman (7 March 2014). "A Search For A Distant Companion To The Sun With The Wide-field Infrared Survey Explorer". The Astrophysical Journal 781 (1).  
  7. ^ a b c d e f g Matese, John J.; Whitmire, Daniel P. (2011). "Persistent evidence of a jovian mass solar companion in the Oort cloud".  
  8. ^ Helhoski, Anna. "News 02/16/11 Does the Solar System Have Giant New Planet?". The Norwalk Daily Voice. Retrieved 10 July 2012. 
  9. ^ Matese, John J.; Lissauer, Jack J. (May 6, 2002). "Continuing Evidence of an Impulsive Component of Oort Cloud Cometary Flux".  
  10. ^ a b Harold F. Levison, Luke Donnes (2007). "Comet Populations and Cometary Dynamics". In Lucy Ann Adams McFadden, Lucy-Ann Adams, Paul Robert Weissman, Torrence V. Johnson. Encyclopedia of the Solar System (2nd ed.). Amsterdam; Boston: Academic Press. pp. 575–588.  
  11. ^ Murray, John B. (1999). "Arguments for the Presence of a Distant Large Undiscovered Solar System Planet". Monthly Notices of the Royal Astronomical Society 309 (1): 31–34.  
  12. ^ Matese, John J.; Whitman, Patrick G.; Whitmire, Daniel P . (1999). "Cometary Evidence of a Massive Body in the Outer Oort Clouds". Icarus 141 (2): 354.  
  13. ^ Matese, John J.; Whitmire, Daniel P.; Lissauer, Jack J. (2006). "A Widebinary Solar Companion as a Possible Origin of Sedna-like Objects". Earth, Moon, and Planets 97 (3–4): 459–470.  
  14. ^ Plait, Phil (February 14, 2011). "No, there’s no proof of a giant planet in the outer Solar System". Discovery Magazine. Retrieved February 15, 2011. 
  15. ^ "Orbital period of a planet at a distance of 15000 AU with a circular orbit". Retrieved February 15, 2011. 
  16. ^ "Have UL Physicists Identified a New Planet?". University of Louisiana. 2011-02-14. Retrieved 2011-02-16. 
  17. ^ "Search on for Tyche, believed to be largest planet in the Solar System".  
  18. ^ Bruce Dorminey (2013-03-31). "Sun May Still Have Low-Mass Solar Companion, Say Astrophysicists Searching NASA WISE Mission Data". Forbes. Retrieved 2013-04-01. 
  19. ^ Sayanagi, Kunio M. (March 2, 2011). 9th planet? Getting the full story"10th"Where is Tyche, the .  
  20. ^ "NASA Releases New WISE Mission Catalog of Entire Infrared Sky". Nasa JPL. 2012-03-14. Retrieved 2012-03-15. 
  21. ^ Wide-field Infrared Survey Explorer
  22. ^ Luhman, K. L. (2014). "A Search for a Distant Companion to the Sun with the Wide-field Infrared Survey Explorer".  
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