Contributed talk at PLATO Mission Conference 2021. Abstract: Evaporation of hydrogen and helium is now directly observable for exoplanets of Jupiter and Neptune size, by using high-resolution spectral observations in the ultraviolet and in the infrared. For even smaller planets, the ongoing loss of a primordial hydrogen-helium atmosphere has not been directly observed yet, but is thought to be relevant for the formation of a habitable atmosphere for life as we know it. The observability of helium escape depends critically on an exoplanet's irradiation in the high-energy regime. M dwarfs, typically a favourite target for habitable zone exoplanet observations, are at a disadvantage here due to their coronal elemental abundance patterns. However, K dwarfs present a suitable starting point for detecting helium escape from planets in their habitable zones, due to their favorable coronal abundances and their higher magnetic activity level compared to G dwarfs. I will discuss relevant examples and outline the impact that modern high-energy surveys can have on the optimal target selection for observing exoplanetary atmospheric escape.

Research funded by the German "Leibniz-Gemeinschaft" under project number P67/2018.