Evolutionary History of the Atmosphere of the Young Mini-Neptune HD 207496b

Abstract

The results of modeling of the escape of the primary atmosphere under the influence of the heat flux from the core for the exoplanet HD 207496b are considered. It is shown that this mechanism of gas envelope loss is not effective enough due to the relatively low equilibrium temperature of the exoplanet, as well as the relatively large mass. Previously, the high efficiency of photoevaporation of a hydrogen–helium atmosphere under the influence of extreme ultraviolet radiation was shown for HD 207496b (Barros et al., 2023). It has been demonstrated that if HD 207496b has a rocky core without a water mantle, surrounded by an envelope of primary composition, then the mass of the atmosphere should be about 0.5% of the mass of the exoplanet, and the gas envelope will be completely lost after about 500 million years. In this case, the initial mass fraction of the primary atmosphere for HD 207496b should have been about 2.2% (the age of the exoplanet is about 520 million years). However, the escape mechanism driven by the core’s heat flow cannot lead to significant atmospheric loss in this case. At the same time, the obtained result strongly depends on the equilibrium temperature and mass of the exoplanet. Accordingly, HD 207496b may be quite close to the boundary where the influence of core heat flow on gas envelope evolution becomes significant, and the obtained result becomes model-dependent. In this regard, it is advisable in future studies to consider several additional factors: the possibility of a water mantle, radiogenic heat flow, and tidal effects.