Radiation

UVC-Intense Exoplanets May Not Be Uninhabitable: Evidence from a Desert Lichen

By Keith Cowing
Status Report
Astrobiology
June 30, 2025
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UVC-Intense Exoplanets May Not Be Uninhabitable: Evidence from a Desert Lichen
Clavascidium lacinulatum (basionym Placidium lacinulatum) Source: Consortium of Lichen Libraria

Many of the recently discovered Earth-like exoplanets are hosted by M and F stars, stars that emit intense UVC, especially during a flare.

We studied whether such planets are nevertheless habitable by irradiating a desert lichen, Clavascidium lacinulatum, with 254-nm 55 W/m2 UVC nonstop for 3 months in the laboratory. Only 50% of its algal photobiont cells were inactivated.

To put this in perspective, we used the same setup to challenge the photobiont cells but grown in pure culture, and Deinococcus radiodurans, the most radiation-resistant bacterium on Earth.

Entire monolayers of hundreds of cells were inactivated in just 60 s. Further studies indicated that the cortex of the lichen was rendered UVC-opaque by deposits of phenolic secondary metabolites in its interstices.

The lichen was injured only because, while most photochemical reactive oxygen species were quenched, photochemical ozone was not. We conclude that UVC-intense exoplanets are not necessarily uninhabitable to photosynthetic organisms.

Astrobiology

Explorers Club Fellow, ex-NASA Space Station Payload manager/space biologist, Away Teams, Journalist, Lapsed climber, Synaesthete, Na’Vi-Jedi-Freman-Buddhist-mix, ASL, Devon Island and Everest Base Camp veteran, (he/him) 🖖🏻