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Kepler-90 (also KOI-351) is a main-sequence star with a planetary system that has the second-largest number of observed exoplanets in the Milky Way. It is approximately 2,500 light years from Earth. Kepler-90 is notable for the configuration of its planetary system, which has similarities to the Solar System in which the rocky planets are nearer and gas giants further away. The five inner planets are either super-Earths or mini-Neptunes due to their size. The two outer planets are gas giants. The outermost known planet orbits its host star at about the same distance as Earth from the Sun. Kepler-90 is designated as KOI-351. During its observation from 2008–2013 it provided evidence for the existence of exoplanets using the transit method, which shows the size of a planet but not its mass. The planets are named based on their distance to the star. Kepler-90b is the innermost and Kepler-90h the outermost of the seven known planets. Kepler-90 was used to test "validation by multiplicity" confirmation method for Kepler planets. Six inner planets met all the requirements for confirmation. The outermost planet showed transit timing variations indicating that this is a real planet as well.〔http://www.nasa.gov/sites/default/files/files/arXivValidationMultisII.pdf〕 ==Planetary system== The seven planets are divided to two inner rocky Earth-sized planets, three middle mini-Neptunes and two outer gas giants. Some of these planets show significant transit-timing variations. . 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「Kepler-90」の詳細全文を読む スポンサード リンク
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