[P-AE20] 系外惑星

[PAE20-12] 地球類似惑星の発見に向けたWSO-UV/UVSPEX計画の現状

*亀田 真吾¹、長田 直也¹、小玉 貴則²、村上 豪³、塩谷 圭吾³、生駒 大洋⁴、成田 憲保⁵、寺田 直樹⁶、藤原 均⁷ (1.立教大学理学部、2.ボルドー大学、3.宇宙航空研究開発機構宇宙科学研究所、4.東京大学 大学院理学系研究科 地球惑星科学専攻、5.国立天文台、6.東北大学大学院理学研究科、7.成蹊大学理工学部)

キーワード：系外惑星、地球型惑星、高層大気

The World Space Observatory for Ultraviolet (WSO-UV) is an orbital optical telescope with a 1.7-m diameter primary mirror currently under development. The WSO-UV is aimed to operate in the 115- to 310-nm UV spectral range. Its two major science instruments are UV spectrographs and UV imaging field cameras with filter wheels. The WSO-UV project is currently in the implementation phase, with a tentative launch date in 2023. As designed, the telescope field of view in the focal plane is not fully occupied by instruments. Recently, two additional instruments devoted to exoplanets have been proposed for WSO-UV, which are the focus of this paper. UVSPEX, a UV-spectrograph for exoplanets, aims to determine atomic hydrogen and oxygen abundance in the exospheres of terrestrial exoplanets. The spectral range is 115 to 130 nm, which enables simultaneous measurement of hydrogen and oxygen emission intensities during an exoplanet transit. A study of exosphere transit photometric curves can help differentiate among different types of rocky planets. The exospheric temper- ature of an Earth-like planet is much higher than that of a Venus-like planet because of the low mixing ratio of the dominant coolant (CO2) in the upper atmosphere of the former, which causes a large difference in transit depth at the oxygen emission line. Thus, whether the terrestrial exoplanet is Earth-like, Venus-like, or other can be determined.