Abstract:
The habitability of any planet is decided by a complex evolution of its interior and atmosphere. Recently in many observations, it has been found that close-in exoplanets are going through significant atmospheric mass loss, which could affect the overall evolution of the exoplanet atmosphere. This atmospheric mass loss of exoplanets is very much dependent on the plasma and radiation environment of their parent stars (e.g., stellar radiation, stellar wind, stellar flares, and Coronal Mass Ejections (CMEs). In this talk, I will explain different physical processes (e.g., Jeans escape, hydrodynamic escape) by which an exoplanet can lose its atmosphere. One major process that leads to significant loss of exoplanetary atmosphere is the stellar radiation-driven atmospheric outflow. Once planetary outflow is initiated from the planet by stellar radiation, it further interacts with the stellar wind shaping up the exoplanetary atmosphere (sometimes producing a comet-like structure) and its atmospheric mass-loss rate. Moreover, flares and coronal mass ejections (CMEs) from the star will also have a great impact on planetary mass loss. I will present our newly developed 3D radiation magnetohydrodynamics model where we have implemented a self-consistent radiative transfer of incident stellar radiation to simulate planetary outflow and its interaction with the stellar wind, CMEs, and flares. I will show that radiation-driven planetary outflow alone can not explain the observed transit signatures & corresponding mass-loss rate, but the interaction with the stellar wind/coronal mass ejections can explain the observed mass-loss rate and transit for many exoplanets. I will also discuss briefly the effect of stellar and planetary magnetic fields on the atmospheric mass-loss rate and corresponding observational signatures.