How Habitable Are M Dwarf Exoplanets? Modeling Surface Conditions and Exploring the Role of Melanins in the Survival of <i>Aspergillus niger</i> Spores Under Exoplanet-Like Radiation

Exoplanet habitability remains a challenging field due to the large distances separating Earth from other stars. Using insights from biology and astrophysics, we studied the habitability of M dwarf exoplanets by modeling their surface temperature and flare ultraviolet (UV) and X-ray doses using the martian atmosphere as a shielding model. Analyzing the Proxima Centauri and TRAPPIST-1 systems, our models suggest that Proxima b and TRAPPIST-1 e are likeliest to have temperatures compatible with surface liquid water, as well as tolerable radiation environments. Results of the modeling were used as a basis for microbiology experiments to assess spore survival and germination of the melanin-rich fungus <i>Aspergillus niger</i> to exoplanet-like radiation (UV-C and X-rays). Results showed that <i>A. niger</i> spores can endure superflare events on M dwarf planets when shielded by a Mars-like atmosphere or by a thin layer of soil or water. Melanin-deficient spores suspended in a melanin-rich solution showed higher survival rates and germination efficiency when compared to melanin-free solutions. Overall, the models developed in this work establish a framework for microbiological research in habitability studies. Finally, we showed that <i>A. niger</i> spores can survive harsh radiation conditions of simulated exoplanets, which also emphasizes the importance of multifunctional molecules like melanins in radiation shielding beyond Earth.