Surface and Oceanic Habitability of terrestrial planets under impacts of flares

The habitability of a planet can be severely affected by the activity of its host star. Several young solar type and fully convective stars observed by the Kepler and K2 missions produce superflares that are up to a thousand times more energetic than those of the Sun. These superflares can increase the level of UV irradiation received by the planet. Thus, if there is no atmosphere capable of attenuating this UV flux, life present on the planet surface will be at risk.

Here we analyse the impact of the UV radiation from these superflares on living organisms on the surface or in the ocean of orbiting planets in the habitable zone of the star. Two active stars are analysed here, Kepler-96 (solar type) and TRAPPIST-1 (M dwarf). Both stars generate powerful flares in short timescales. Kepler-96 harbours a Super-Earth orbiting very close to the star, impossible to be habitable due to its proximity to the star. Nevertheless, its age of 2.3 Gyrs allows us to analyse the impact of a flaring young Sun-like star in a hypothetic Earth-like planet. The TRAPPIST-1 system has three planets in the habitable zone of the star. The estimated UV flux produced by the superflares of both stars implies that life would only survive on the surface of these planets if there was already an ozone layer present on the planet atmosphere. If that is not the case, life could survive below an ocean surface.