[A-OS10] 陸域海洋相互作用ー惑星スケールの物質輸送

[AOS10-07] The Atmospheric Response of Earth-like Exoplanets to X-ray and Extreme UV emission from G-M planet hosts: Case of TOI-700b

★Invited Papers

*Vladimir Airapetian¹、Jared M. Bell¹、Alex Glocer¹ (1.NASA Goddard Space Flight Center, USA)

キーワード：Earth, exoplanets, atmospheric dynamics, atmospheric escape

Recent Kepler, TESS, HST and ground-based observations of G-M planet hosts suggest that exoplanets around them should be exposed to high level of ionizing radiation in the form of stellar coronal and flare driven X-ray and Extreme UV (XUV) and wind fluxes. What is the impact of this high-energy radiation on atmospheres of rocky exoplanets? The answer to this question is one of the central issues to exoplanetary habitability, because the presence of a thick high molecular weight atmosphere over sufficiently long timescales is crucial factor associated with planetary surface pressure and its exposure to stellar UV and particle irradiation. Here we present the modeling results of thermodynamics and atmospheric dynamics of an Earth-like exoplanet controlled by quiescent coronal XUV emission from K and M dwarfs. We show that ionospheric escape is the dominant process in atmospheric escape at the XUV flux ~ 1- 10 times of the solar flux with the escape rate of nitrogen ions approaching the rate of oxygen ion escape. Our models suggest that the transition from ion escape to hydrodynamic escape occurs at ~ 60 times of the XUV solar flux. We discuss the implications of the atmospheric escape due to XUV driven photoionization driven heating and Joule heating rate for a magnetized planet and habitability conditions for a recently discovered Earth-like exoplanet, TOI-700d, around a quiet M2 dwarf star.