Abstract EANA2024-73

In the last decades, there has been an increasing amount of research dedicated to the study of the potential conditions of planetary bodies to host life. As stellar radiation can have impact on the planet having effects at environmental and biological levels it appears as a fundamental factor to be analysed. It is now well established that the X-ray and extreme UV radiation (XUV) radiation as well as UV radiation (UVR) affects the potential habitability of planets. In extreme cases the XUV-radiation can erode a planetary atmosphere and can cause a significant water-loss of the planet. In less extreme cases, the XUV may still lead to increase atmospheric scape and ionization of the atmosphere of the planet.  The XUV-radiation can also affect living organisms directly on planets without an atmosphere. It is also now well established that flares, which are sudden outbreaks of stellar radiation, significantly increase the amount of XUV-radiation and UVR. Furthermore, Coronal-Mass Ejections are often associated with large flares which then lead to a high flux of charged particles. In order to assess the role of flares in habitability, we first have to answer the question whether most of the radiation comes out in rare but large flares, or in frequent but small flares. We demonstrate that the flare-frequency distribution is a broken power-law, and that the average emission from rare but large flares is much larger than from the frequent small flares.  Moreover, from the point of view of their biological effects, flares and superflares have been poorly investigated. As part of our EXO-UV programme, we aim to study the impact of these events at UV wavelengths by using an interdisciplinary approach where we experimentally investigate the effects of UVR from flares and superflares on microbial life forms.  In this talk we will also present our latest results related to the biological impact of a superflare case on the surface of the TRAPPIST-1 planets (e,f,g). Contrary to the conclusions of previous studies, we demonstrate that a fraction of the population of microorganisms could survive –unshielded– the harsh conditions imposed by this highly energetic event on these planets.