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Tyche (hypothetical planet)
Tyche is 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.〔〔 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 and Whitmire〔(【引用サイトリンク】title=Daniel P. Whitmire )〕 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.〔 In 2014, NASA announced that the WISE survey had ruled out any object with Tyche's characteristics, indicating that Tyche as hypothesized by Matese, Whitman, and Whitmire does not exist.〔〔
==History==
Matese, Whitmire and their colleague Patrick Whitman first proposed the existence of this planet in 1999,〔 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.〔 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.〔 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.〔〔 They also suggested that such an object might explain the trans-Neptunian object Sedna's peculiar orbit.〔 However, the sample size of Oort comets was small and the results were inconclusive.〔
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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