Modelling the effect of stellar metallicity on the XUV evolution of low-mass stars and its impact on exoplanet atmospheres/habitability

ABSTRACT Understanding how exoplanet atmospheres evolve is a key question in the context of habitability. One key process governing this evolution is atmospheric evaporation by stellar X-ray and EUV (extreme ultraviolet) emission (collectively, XUV). As such, the evolution of exoplanet atmospheres is closely tied to the evolution of the host star’s magnetic activity. Many studies have modelled the combined evolution of exoplanet atmospheres and their host stars. However, to date, the impact of the host star’s metallicity on stellar activity/exoplanet atmosphere evolution has not been explored. In this work, we investigate how stellar metallicity affects the rotation and activity evolution of solar-like stars as well as the corresponding exoplanet atmospheric evolution. We reconfirm previous results that metal-rich stars spin-down more rapidly than metal-poor stars. We also find that the XUV flux that an exoplanet in the habitable zone of its host star receives is larger when the host star is more metal-rich. As such, the atmospheres of exoplanets in the habitable zones of metal-rich stars are evaporated more rapidly than exoplanets in the habitable zones of metal-poor stars. Lastly, we find that the atmospheric evolution is most sensitive to the host star’s metallicity when the host star has a higher mass. In the highest mass solar stars, the metallicity can have a larger influence on the atmospheric evolution than the initial rotation period of the star.