I am interested in how atmospheres evolve, and especially in transitions to and from habitable states. My primary expertise is in atmospheric loss processes, and more specifically in the loss to space of charged particles from atmospheres driven by interactions with the planet’s host star. A guiding question for my research at present is whether habitable worlds require global magnetic fields, and I currently lead a team science center funded by NASA Heliophysics to answer this question. My research group uses spacecraft observations from terrestrial planets in our solar system, and simulations of atmospheric escape from terrestrial words (both in and out of our solar system). I also have interests in magnetospheric physics (e.g. aurora, reconnection) and the influence of asteroid and comet impacts on atmospheric evolution.