Monday

Solar coronal mass ejections (CMEs) produce adverse space weather effects at Earth. Planets in the close habitable zone of magnetically active M dwarfs may experience more extreme space weather than at Earth, including frequent CME impacts leading to atmospheric erosion and leaving the surface exposed to extreme flare activity. We have developed a model, Forecasting a CME's Altered Trajectory (ForeCAT), which predicts a CME's deflection. We adapt ForeCAT to simulate CME deflections for the mid-type M dwarf V374 Peg. V374 Peg's strong magnetic fields can trap CMEs at the M dwarf's Astrospheric Current Sheet, that is, the location of the minimum in the background magnetic field. The probability of planetary impact decreases with increasing inclination of the planetary orbit with respect to the Astrospheric Current Sheet, ranging between 0.5-5 CME impacts per day for M dwarf exoplanets. We determine the minimum planetary magnetic field necessary to shield a planet's atmosphere from CME impacts and find that M dwarf exoplanets require values between tens and hundreds of Gauss. These values exceed the magnitude required to shield a planet from the stellar wind, suggesting that CMEs may be the key driver of atmospheric losses.