[P-AE16] Exoplanets

[PAE16-05] Observational implications of atmospheric and orbital evolution of super-Earths

*Naho Fujita¹, Yasunori Hori^2,3, Takanori Sasaki¹ (1.Kyoto University, 2.Astrobiology Center, 3.National Astronomical Observatory of Japan)

Keywords:Exoplanets, Super-Earths, Atmospheric escape, Orbital evolution, Exoplanet observation, M dwarfs

There is a scarcity of close-in small planets with 1.5 to 2.0 times Earth radii and the orbital period of < 100 days in the radius distribution of Kepler planets around FGK stars (Fulton & Petigura 2018) and M dwarfs (Hirano et al. 2018). The so-called “radius gap” is considered as the radius boundary between planets with atmospheres and those without atmospheres. The atmospheric escape of small planets by photoevaporation can explain the origin of the observed radius gap (e.g., Owen & Wu 2017). Previous studies, however, assumed that evaporating planets stay in situ. Planets that undergo mass loss should move outward while conserving the total angular momentum of the star-planet system. In this study, we calculated the orbital evolution of close-in super-Earths that undergo hydrodynamic escape of their atmospheres driven by stellar X-ray and UV irradiations. We found that a radius gap, as seen in observations, appears in the orbital period-radius distribution of close-in super-Earths. Our results also suggest that the atmospheric escape of planets strongly affects the final orbital configuration of the planetary systems. More super-Earths orbiting M dwarfs are expected to be discovered by ongoing near-infrared doppler surveys, such as CFHT/SPIRou, Subaru/IRD, and VLT/CRIRES. Therefore, our theoretical study on the orbital evolution of close-in super-Earths helps understand their formation history and dynamical evolution.