WSO-UV/UVSPEX for Earth-like exoplanets

Presenter: Shingo KAMEDA
Many Earth-sized planets have been discovered and some appear to lie in the habitable zone. Moreover, several Earth-sized planets were recently detected around low temperature stars near the solar system. However, it is difficult to characterize them as Earth-like or Venus-like. Transit spectroscopy for exoplanetary atmosphere has been performed to characterize larger exoplanets but it requires very high accuracy because of their small size. Recently, Earth’s hydrogen exosphere was re-investigated and it was revealed that the Earth’s exosphere is extended to ~ 38 Earth radii. On the other hand, Venus’ and Mars’ hydrogen exosphere is not so much extended because of its low temperature of upper atmosphere. This is caused by the difference of mixing ratio of CO2 in the upper atmosphere. Venus and Mars have CO2-rich atmospheres with a lower exospheric temperature. On Earth, CO2 was removed from its atmosphere by a carbon cycle with its ocean and tectonics. The expanded exospheres can be observed in UV, during the exoplanet transit event in a primary eclipse. To realize exoplanet transit observations in oxygen spectral lines with the desired accuracy, we equip the WSO-UV telescope (1.7 m) with the UVSPEX spectrograph.