The EXO-UV Program: Latest Advances of Experimental Studies to Investigate the Biological Impact of UV Radiation on Exoplanets

The EXO-UV program is an international, interdisciplinary collaboration between astrophysicists and biologists aimed at expanding the characterization of ultraviolet radiation (UVR) environments on exoplanets. UVR is particularly relevant because it reaches the surface of planets and can influence their habitability. High UVR fluxes emitted during flares and superflares are of particular interest due to the limited information available regarding their biological impact and the lack of experimental studies to evaluate their influence. Our first initial study in the EXO-UV program focused on experimentally studying the potential biological impact of a flare and a superflare on Proxima b, and the second considered a superflare on the TRAPPIST-1 system planets e, f, g. The survival of microorganisms belonging to both the Bacteria and Archaea domains (Deinococcus radiodurans, Pseudomonas aeruginosa, Escherichia coli, Haloferax volcanii) was evaluated. Microorganisms were exposed to UVR (UVC = 254 nm) at fluence rates and fluences equivalent to those they would receive from flares and superflares on the unshielded surfaces of these planets. Our results show the existence of a small fraction of the cell population that can tolerate these high fluences, suggesting that previous research underestimated the ability of “life as we know it” to withstand these high UVR fluxes. These results also document the tolerance of well-known microorganisms to high fluences of UVR related to flares and superflares in quantities and at wavelengths that these microorganisms do not experience on the present Earth.