Modeling Photoprotection of Ultraviolet C Radiation by Ferric Ions and Implications for the Habitability of Ancient Martian Lakes

On Mars, the amount of ultraviolet C (UVC) radiation that reaches the surface is sufficiently deleterious for life as we know it. However, it has been predicted that some ancient lakes on Mars had high concentrations of Fe³⁺, an ionic species known for a high absorption of UVC radiation. Some models of UV attenuation have already been established; however, there is a lack of reliable simulations that make the connection between this radiation absorption in an aqueous medium and its impact on the viability of microorganisms. This work proposes a simple model to estimate the viability of microorganisms irradiated in solution with different concentrations of Fe³⁺ and constrains the lethal UVC dose in these conditions. In experimental assays, the median lethal dose of <i>Saccharomyces boulardii</i> increased consistently with the model's predictions, which thereby demonstrated the model's predictive validity. This ability was then used in a case study to simulate the viability of life in a Fe³⁺-containing lake on ancient Mars. Although the actual conditions of this kind of environment are not known, the simulations showed that lakes with small water columns that contain Fe³⁺ should have been able to protect growing microorganisms. This model enhances the ability to assess potentially habitable conditions on ancient Mars. Key Words: Photoprotection-UVC radiation-Fe³⁺ ions-Mars-Astrobiology. Astrobiology xx, xxx-xxx.