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WASP-15b is an extrasolar planet discovered in 2008 by the SuperWASP collaboration, which seeks to discover exoplanets that transit their host stars. The planet orbits its host star at a distance of 0.05 AU every four days. The mass of this planet is about one half that of Jupiter, but its radius is nearly 50% larger than Jupiter's, making the density of this planet only one quarter that of water; it is thought that some other form of heating must explain its extremely low density.〔 WASP-15b's discovery was published on April 29, 2009. ==Discovery== WASP-15 was first observed by the WASP-South branch of the SuperWASP project, which operates from the South African Astronomical Observatory, between May 4, 2006 and July 17, 2006. It was later observed by both WASP-South and SuperWASP-North, which is based in the Canary Islands, from January 31, 2007 to July 17, 2007 and from January 31, 2008 to May 29, 2008.〔 Further analysis taken from 24,943 collected data points revealed eleven full or partial transits.〔 Follow-up observations were conducted by a European and American science team at the 1.2 m Leonhard Euler Telescope at La Silla Observatory in Chile, which further raised the possibility of the existence of a planet in WASP-15's orbit; use of the CORALIE spectrograph on the Euler Telescope between March 6, 2008 and July 17, 2008 revealed that the variations in radial velocity measurements were not because of an eclipsing binary star system.〔 CORALIE and the High Resolution Echelle Spectrometer (HIRES) revealed the spectrum of WASP-15, which was used to derive the star's characteristics.〔 The science team studying WASP-15 found that, after running best-fit models, WASP-15's radial velocity and transit shifts were most likely due to the existence of a planet.〔 WASP-15's planet, WASP-15b, had one of the lowest densities known amongst extrasolar planets when it was discovered. Its discovery paper was published by the American Astronomical Society on April 29, 2009 in the ''Astronomical Journal''.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「WASP-15b」の詳細全文を読む スポンサード リンク
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