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17 Thetis is a large main-belt asteroid that was discovered by R. Luther on April 17, 1852. It was his first asteroid discovery. The name comes from Thetis, the mother of Achilles in Greek mythology. One Thetidian stellar occultation was observed from Oregon in 1999. However, the event was not timed. The spectrum of this object indicates that it is an S-type asteroid with both low and high calcium forms of pyroxene on the surface, along with less than 20% olivine. The high-calcium form of pyroxene forms 40% or more of the total pyroxene present, indicating a history of igneous rock deposits. This suggests that the asteroid underwent differentiation by melting, creating a surface of basalt rock.〔 ==Mass== The mass of Thetis has been calculated from perturbations by 4 Vesta and 11 Parthenope. In 2007, Baer and Chesley calculated Thetis to have a mass of 1.2 kg〔(Mass of Thetis 0.00617 / Mass of Ceres 4.75) * Mass of Ceres 9.43E+20 = 1.224E+18〕 with a density of 3.21 g/cm³.〔 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「17 Thetis」の詳細全文を読む スポンサード リンク
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