  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 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 of the melanin-rich fungus
Aspergillus niger to exoplanet-like radiation (UV-C and X-rays). Results showed
that A. niger 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 A.
niger spores can survive harsh radiation conditions of simulated exoplanets,
also emphasizing the importance of multifunctional molecules like melanins in
radiation shielding beyond Earth.
