[P-CG19] Planetary Magnetosphere, Ionosphere, and Atmosphere

[PCG19-P02] Atmospheric hydrodynamic escape in early Earth driven by celestial impacts during the Late Heavy Bombardment Period

*Tatsuki Nawa¹, Tomoki Kimura¹, Tatsuya Yoshida² (1.Tokyo University of Science, 2.Tohoku University)

Keywords:Earth, atmosphere

The primordial atmosphere of early Earth was likely formed from hydrogen-based solar nebula gas and from water vapor and carbon dioxide ejected from the Earth's interior by celestial collisions and other events. The atmospheric gases were lost by hydrodynamic escape from the early Earth (Yoshida et al., 2020). About 3.8 billion years ago, when life emerged, the Earth was in the middle of or just after the Late Heavy Bombardment Period (LHBP) with frequent celestial impact events. Although there are many studies addressing atmospheric escape due to a single large-scale impact event (Shuvalov et al., 2013), there has been no study for atmospheric escape due to heating via frequent and small celestial impact events during LHBP. Therefore, the total contribution of the celestial impacts to early Earth's atmospheric escape has not been quantified. In this study, we combined a numerical model of hydrodynamic escape due to solar X-ray - Ultraviolet (XUV) heating proposed by Yoshida et al. (2021) with our newly developed model for the atmospheric heating by small-scale frequent celestial impact events as a new energy source, with which we assess the effect of celestial impact events on the Earth's atmospheric environment when life began. Based on the impact flux distribution measurement with respect to the diameter of craters formed in the lunar Nectaris basin (Marchi et al., 2012) and the scaling law between the crater and impactor diameters (Morbidelli et al., 2018), we obtained a relation between the impactor diameter and impact flux during the late heavy bombardment. With the obtained impactor diameter-flux relation and an analytical model for the kinetic energy of an impactor entering the atmosphere (Collins et al., 2005), we derived the altitude distribution of the atmospheric heating rate by the impactors during celestial impact events over a period of about 200 million years. We are going to implement this impactor heating rate in the hydrodynamic escape model of Yoshida et al. (2021). The current status will be presented in this presentation.