| Abstract |
Recent theoretical studies have shown that thermal escape of planetary atmospheres exposed to intense XUV irradiation is suppressed by molecular radiative cooling (Yoshida and Kuramoto, 2020, 2021; Yoshida et al., 2022) and by atomic radiative cooling (Nakayama et al., 2022), resulting in a significant reduction of thermal escape rate. This reduction requires us to reconsider the evolutionary scenario of planetary atmospheres established so far, and suggests that non-thermal escape may have played an important role in the early evolutionary phase of planetary atmospheres as well as in the late phase. Previous fluid models predicted that an Earth-like atmosphere exposed to XUV irradiation several times greater than that of the present-day Earth would undergo slow hydrodynamic escape and highly expand, with the exobase altitude reaching several times the planetary radius. In this presentation, I will show using a DSMC model that an extended planetary atmosphere undergoes cooling and contraction by non-thermal escape, and that the thermal escape rate decreases with increasing non-thermal escape rate. |
