Modeling the Atmospheric Evolution of Exoplanets in the Habitable Zone of M-Dwarfs

Overview

The evolution of a planet’s atmosphere depends strongly on the properties of its host star. When their host stars are younger, planets can experience stronger winds and XUV emission. This is particularly true for planets orbiting M-dwarfs due to their close proximity to the host star. To determine if these planets hold an atmosphere, it is necessary to quantify the impact from the stellar wind and XUV fluxes. Here, I determine atmospheric mass loss due to stellar wind and photoevaporation of 4 planets in close orbit and 34 in the HZ. The wind properties and EUV energy of the M-dwarf host stars were calculated through rotation period and X-ray flux scaling through the planet’s lifetime. The mass loss rate was then computed as a function of time, and then accumulated until the planet’s age to determine the total atmospheric mass loss of the planet’s primordial H/He dominated atmosphere. I find that: 1. Stellar wind can only remove a small fraction of the H/He envelope of Earth-sized exoplanets in the HZ of early-type Mdwarfs, therefore photoevaporation is essential for removing significant amounts of H/ He. 2. Planets orbiting at >0.2 AU cannot be stripped of a primordial envelope due to stellar wind or photoevaporation. 3. 11 planets in the study could have lost a primordial envelope. My results will help contextualize the atmospheric data taken by the James Webb Space Telescope. Further, understanding atmospheres through these improved evolutionary models will greatly help guide the search for habitable exoplanets.