Core-Powered Mass-Loss of the Primary Atmospheres of Mini-Neptunes: Influence of Water Content in the Planet Interior and Evolution of the Host Star

Abstract — The dependence of the rate and magnitude of the core-powered mass-loss of the primary atmosphere by mini-Neptunes on the water content in the core has been studied. It was shown (Evdokimov and Shematovich, 2025a, 2005b) that the magnitude of the loss of the hydrogen–helium envelope due to the heat flux from the core strongly depends on the structure of the interior of the mini-Neptune HD 207496b. The presence of a water mantle, which makes up a significant portion of the planet’s mass, increases the core radius and its heat capacity, leading to increased atmospheric losses. In this study, we conducted a more detailed analysis of this effect by simulating the escape of the primary gas envelope for mini-Neptunes with varying water mass fractions, given their mass, initial atmospheric mass fraction, and equilibrium temperature. The calculations were performed both for model planets with specified parameters and for HD 207496b, taking into account previously unstudied factors such as the radiogenic heat source and the evolution of the host star. The strong dependence of the loss of the primary atmosphere on the water content in the planet interiors of mini-Neptunes was confirmed. The significant influence of the early evolutionary stages of the host stars on the history of their primary gas envelopes was demonstrated. It has been shown that the heat flow due to the presence of radionuclides (including aluminum-26) in the silicate mantle of mini-Neptunes has almost no effect on the process of loss of the primary gas envelope, provided that the content of radionuclides corresponds to the content of chondrite matter in the early Solar System.