The variable activity of stars such as the Sun is mediated through stellar magnetic fields, radiative and energetic particle fluxes, stellar winds and magnetic storms manifested as stellar flares and coronal mass ejections. This activity influences planetary atmospheres, climate and habitability: on the one hand it drives life-sustaining processes on planets, but on the other hand can adversely impact planetary environments rendering them uninhabitable. Studies of this intimate relationship between the parent star, its astrosphere and the planets that it hosts have reached a certain level of...