Speaker: Daria Kubyshkina (Space Research Institute, Graz)
Title: Atmospheric mass loss through time: escape mechanisms at early times and influence of stellar evolution
Abstract:
The evolution of the atmospheres of low and intermediate-mass exoplanets is strongly affected by atmospheric mass loss. However, the dominant driving mechanism of atmospheric escape, which contributes most to planetary evolution and forms the observed population of exoplanets, is yet debated. The two most prominent drivers are the own post-formation cooling luminosity of a planet and the high-energy irradiation of the host star. The concurrent effect on planetary evolution from both sources depends on basic planetary parameters, such as mass and orbital separation, and on the starting conditions after protoplanetary disk dispersal, such as the initial atmospheric mass fraction and post-formation luminosity of a planet. Aside from planetary parameters, the input from atmospheric mass loss driven by stellar irradiation depends on the type of the host star and on its activity at the early stages of evolution, which can be drastically different even for stars of the same type.

In this talk, I will present a comparative study of a range of sub-Neptune-like exoplanets evolving under different conditions performed using our framework combining planetary (thermal) evolution in MESA with the realistic prescription of the atmospheric escape based on hydrodynamic modeling. I will discuss the influence of the initial conditions predicted by formation models, stellar evolution paths, and particular escape mechanisms on planetary evolution, at young ages and on Gyr-timescales. Our work demonstrates that the primary driver of atmospheric escape is not the same for different regions of the planetary/stellar parameter space and also for different stages of evolution. Thus, the final state of an individual planet (and to some extent, of the whole planetary population) depends on the host star properties and planet type. In particular, the differences in stellar evolution paths have a bigger effect on planetary evolution for stars close to solar mass or heavier, while for lower mass stars the initial conditions of a planet appear to be more important.