Seminar: CPS Seminar
date: 2023 April 3 (Mon) 15:00-17:00
Room: CPS Conference Room and Online (Hybrid meeting)
Speaker1: TERADA Naoki (Professor,Tohoku University)
Title: "DSMC simulations of an extended planetary atmosphere"
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.
Keywords: Atmospheric escape, non-thermal escape, extended atmosphere
Speaker2: YOSHIDA Tatsuya(JSPS Research Fellow,Tohoku University)
Title: "Hydrodynamic escape and evolution of a reduced proto-atmosphere on Earth"
Abstract: Recent cosmochemical studies have shown that most of Earth’s building blocks were close to enstatite meteorites in isotopic compositions. This implies the formation of an impact-induced proto-atmosphere enriched in H2 and CH4 on accreting Earth. Such a reduced atmosphere may have played an important role in the prebiotic chemical evolution since the efficient synthesis of organic matter could be expected. On the other hand, the reduced atmosphere is expected to have changed with time through hydrodynamic escape induced by the strong XUV irradiation from the young Sun and photochemical reactions of reduced chemical species. In this talk, I will mainly show the results of our hydrodynamic escape simulations and a possible scenario of the early Earth’s atmosphere estimated by the calculation results. I will also talk about the comparison with the atmospheric escape of an early Martian atmosphere and the application to the atmospheric escape of exoplanets if I have time to spare.
Keywords: Atmospheric escape, proto-atmosphere, Earth
Organizer: HAYASHI Yoshiyuki