Authors

Masahiro Ikoma, Yasunori Hori

Affiliations

Tokyo Institute of Technology

Abstract

A hydrogen atmosphere of rocky planets is a natural by-product of planet formation in the context of the core accretion model. While such a hydrogen atmosphere makes up only a small fraction of the planet’s total mass compared to gas giants’ hydrogen envelopes, it has a great influence on planetary surface environments: It is capable of bringing water, and affects the redox state which may be relevant to the origin of life. Whether a rocky planet captures a significant amount of the surrounding disk gas to form a hydrogen atmosphere depends on planetary accretion and protoplanetary-disk evolution. In this paper, we show results of our numerical simulations of accumulation of hydrogen atmospheres that incorporate the recent picture of planetary accretion and protoplanetary-disk evolution. Our results suggest that there are several different types of Earth-like exoplanets to be detected (hydrogen-covered planets, vapor planets, and ocean planets), depending on planet mass and distance to the host star. Future observations of Earth-like planets’ atmospheres are helpful to improve theories of planet formation especially in the inner protoplanetary disk.