3D Modelling of the Impact of Stellar Flares on Earth-like Rocky Planets Orbiting M Dwarf Stars

The current best candidates for habitable exoplanets have been detected orbiting M-dwarf stars. Such stars are quite common, and their low brightness and the short orbital periods of their planets both aid observations. Many M dwarf stars are known to produce stellar flares, phenomena where the star releases substantial amounts of energy, particularly in the ultraviolet (UV) and becomes much brighter for a period of minutes to hours. In addition, flares are associated with a release of energetic protons from the star, known as stellar proton events. Flares released by the Sun are less energetic than those of M dwarfs. This presents some questions about the habitability of exoplanets around M dwarfs. The increased UV light and the protons may induce long-term changes in the exoplanetary atmosphere by destroying molecules such as ozone that help shield the surface from the UV. This would make the planets surface dangerous for terrestrial life and may make the emergence and survival of surface-based life impossible. I present results from a study in 3D using the UK Met Office global circulation model, termed the Unified Model (UM). The UM has been adapted to model a wide range of exoplanets. I present the results from simulations including a coupled chemical kinetics and photolysis scheme. Our chemical network describes the production of ozone via the Chapman cycle as well as the change in ozone due to HOx and NOx photochemistry. A tidally locked aquaplanet with an Earth-like atmosphere is simulated for twenty years under quiescent conditions before it is subjected to a series of flares of varying total energies drawn from a realistic distribution. I will describe the changes in the atmospheric composition as well as surface habitability that occur due to the flares.