The magnetised plasma streaming outward from the Sun profoundly influences planetary systems, shaping their magnetospheric environments and atmospheric properties. At Earth, extreme solar wind conditions can drive powerful auroral currents through the atmosphere and even the ground, triggering northern lights at low latitudes and posing a direct threat to modern society. In the outer solar system, where solar photon flux is diminished, solar wind–magnetosphere interactions become increasingly dominant and have been strongly linked to large declines in atmospheric temperatures across the past few decades.

In this talk, I will start with extreme solar eruptions, in particular coronal mass ejections (CMEs), and discuss how we model and understand their propagation through the heliosphere. I will present modelling of the magnetospheric response to such extreme events, and show how insights gained from our own planet can advance our understanding of other planetary and even exoplanetary systems. Finally, I will highlight the critical need for further observations to constrain theory and models of magnetosphere-atmosphere interactions, and outline a new ESA mission concept, ROARS (Research Observatory for Atmospheric Responses to Sun–magnetosphere interactions), designed to deliver transformative advances to our understanding of star–planet interactions and underpin future forecasting efforts in the increasingly congested environment of Low Earth Orbit.