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HD 209458 b (sometimes though unofficially named Osiris) is an extrasolar planet that orbits the solar analog HD 209458 in the constellation Pegasus, some 150 light-years from the Solar System. The radius of the planet's orbit is 7 million kilometres, about 0.047 astronomical units, or one eighth the radius of Mercury's orbit. This small radius results in a year that is 3.5 Earth days long and an estimated surface temperature of about 1,000 °C (about 1,800 °F). Its mass is 220 times that of Earth (0.69 Jupiter masses) and its volume is some 2.5 times greater than that of Jupiter. The high mass and great volume of HD 209458 b indicate that it is a gas giant. HD 209458 b represents a number of milestones in extraplanetary research. It was the first of many categories: * a transiting extrasolar planet * the first planet detected through more than one method * an extrasolar planet known to have an atmosphere * an extrasolar planet observed to have an evaporating hydrogen atmosphere * an extrasolar planet found to have an atmosphere containing oxygen and carbon * one of the first two extrasolar planets to be directly observed spectroscopically * the first extrasolar gas giant to have its superstorm measured * the first planet to have its orbital speed measured, determining its mass directly.〔 Based on the application of new, theoretical models, as of April 2007, it is alleged to be the first extrasolar planet found to have water vapor in its atmosphere.〔(Water Found in Extrasolar Planet's Atmosphere ) - Space.com〕〔(''Signs of water seen on planet outside solar system'' ), by Will Dunham, Reuters, Tue Apr 10, 2007 8:44PM EDT〕 In July, 2014, NASA announced finding very dry atmospheres on three exoplanets (HD 189733b, HD 209458b, WASP-12b) orbiting Sun-like stars. == Detection and discovery == 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「HD 209458 b」の詳細全文を読む スポンサード リンク
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