Estimating photoevaporative mass loss of exoplanets with PLATYPOS

Abstract

We develop PLATYPOS (PLAneTarY PhOtoevaporation Simulator), a python code to perform planetary photoevaporative mass-loss calculations for close-in planets with hydrogen-helium envelopes atop Earth-like rocky cores. With physical and model parameters as input, PLATYPOS calculates the atmospheric mass loss and with it the radius evolution of a planet over time, taking into account also the thermal cooling and subsequent radius evolution of the planet. In particular, we implement different stellar activity evolution tracks over time. Our setup allows for a prediction of whether a planet can hold on to a significant fraction of its atmosphere, or fully evaporates, leaving behind only the bare rocky core. The user supplies information about the star–planet system of interest, which includes planetary and host star parameters, as well as the star's rotational and thus activity evolution. In addition, several details for the evaporative mass-loss rate estimation can be chosen. This includes the effective absorption cross-section for high energy photons, the evaporation efficiency, and the hydrodynamic escape model.