[P-PS01_30PM2] Toward JUICE and future explorations of outer solar system

[PPS01-09] 木星の影中におけるガニメデ・カリストの予想外の近赤外線輝度の検出

*津村 耕司¹、有松 亘²、江上 英一³、早野 裕⁴、本田 親寿⁵、木村 淳⁶、倉本 圭⁷、松浦 周二¹、美濃和 陽典⁴、中島 健介⁸、中本 泰史⁹、白旗 麻衣¹、スレース ジェイソン¹⁰、高橋 康人⁷、和田 武彦¹ (1.宇宙航空研究開発機構　宇宙科学研究所、2.東京大学、3.アリゾナ大学、4.国立天文台　すばる観測所、5.会津大学、6.東京工業大学　地球生命研究所、7.北海道大学、8.九州大学、9.東京工業大学、10.カリフォルニア工科大学)

キーワード：ガリレオ衛星食, ガニメデ, カリスト, エウロパ, 木星上層大気

The Galilean satellites (Io, Europa, Ganymede, and Callisto) are expected to be dark when eclipsed by the Jovian shadow. However, we have discovered that Ganymede and Callisto are still surprisingly bright at 1.5 μm even when not directly lit by sunlight, based on observations from the Hubble Space Telescope and the Subaru Telescope. Their eclipsed luminosity was one-millionth of their uneclipsed brightness (i.e. 〜50 μJy for Ganymede and 〜30 μJy for Callisto in eclipse), which is low enough that this phenomenon has been undiscovered until now. In contrast, Europa in eclipse was not detected (<5.5 μJy), a potential clue to the origin of the source of luminosity. Likewise, Ganymede was observed at 3.6 μm by the Spitzer Space Telescope but it was not detected either (<3.6 μJy), suggesting a significant wavelength dependence. Why are they luminous even when in the Jovian shadow? These facts may be consistent with sunlight scattered by dust in the Jovian upper atmosphere, and if this is the case, observations of Ganymede and Callisto while eclipsed by the Jovian shadow provide us with a new method to investigate Jupiter's atmospheric composition.