Photoevaporation of Water Dominated Exoplanet Atmospheres

The atmospheres of close-in, low-mass exoplanets are extremely vulnerable to the effects of stellar UV to X-ray radiation. Photoevaporation can significantly ablate planetary atmospheres or even strip them entirely, potentially rendering a planet uninhabitable. Existing hydrodynamical studies of this important atmospheric mass loss mechanism have mainly considered hydrogen/helium dominated atmospheres. Currently, the effect of higher mean compositions on photoevaporative mass loss has only been the subject of a limited number of studies. In the era of more advanced exoplanet atmospheric observations, it is more important than ever to determine what, if any, atmosphere these planets may have been able to retain. Here, we present preliminary results of hydrodynamic simulations, showing a water-rich atmosphere of a low-mass planet undergoing photoevaporation. We show accurate modelling of higher mean molecular weight atmospheres can result in different escape rates than those predicted by current theoretical models.