UV attenuation by Martian brines

Abstract

UV radiation on the surface of Mars is an important factor affecting the survivability of microorganisms on Mars; a habitable niche on Mars would be one that provides protection from harmful UV radiation. The possibility of Martian brines providing a habitable niche on Mars via attenuation of UV radiation is investigated. Minerals could have leached into bodies of water on early Mars and may remain present in the polar ice caps. Aqueous solutions of nine different salts found on the surface of Mars were prepared and UV absorption cross sections were derived in the spectral range 230–400 nm. The salts investigated were Fe(NO3)3, Fe2(SO4)3, FeSO4, FeCl2, MnSO4, CaSO4, MgSO4, MgCl2, and NaCl. UV absorption cross sections found ranged from 10−24 to 10−17 cm2molecule−1, with the cation primarily affecting absorption strength. In particular, salts containing Fe3+ were found to absorb significant amounts of UV radiation. Combining the derived absorption cross sections with the solar radiation at Mars, transmitted UV radiation was simulated for different combinations of depth and salt concentration. Greater than 95% UV absorption from 230 to 400 nm is possible with iron salts at depths and concentrations expected to be found on past and present-day Mars. The results of this work are promising for investigating the habitability of Mars and other rocky planets that lack an atmosphere capable of attenuating UV radiation.

Aquatic Ferrous Solutions of Prebiotic Mineral Salts as Strong UV Protectants and Possible Loci of Life Origin

“…Recent fundamental analysis of UV transmission in prebiotic waters (Ranjan et al, 2022 ) suggests that ferrous waters are strong UV absorbers. Similar results were obtained in a study of UV absorption in martian brines (Godin et al, 2020 ). Those results are aligned with previous experimental work on UV shielding utilizing either instrumental (Cleaves and Miller, 1998 ) or biological detection systems (Gómez et al, 2007 ).…”

“…While the strong UV shielding by ferrous waters appears unfavorable to the UV-origin-of-life scenarios (Ranjan et al, 2022 ), it would be highly advantageous for UV protection of amphiphiles' assembles explored in our scenario (Subbotin and Fiksel, 2023 ). Following the previous reports on UV-shielded properties of ferrous waters (Godin et al, 2020 ; Ranjan et al, 2022 ), we tested the UV-shielding properties of simple and complex salts (FeCl 2 —iron dichloride, FeCl 3 —iron trichoride, Fe(NO 3 ) 3 —ferric nitride, NH 4 Fe(SO 4 ) 2 —ferric ammonium sulfate, and (NH 4 ) 5 [Fe(C 6 H 4 O 7 ) 2 ]—ferric ammonium citrate) that could be present in the Archean waters (Miller and Urey, 1959 ; Handschuh and Orgel, 1973 ; Keefe and Miller, 1996 ; Gómez et al, 2007 ; Breslow et al, 2010 ; Hardy et al, 2015 ; Patel et al, 2015 ; Sproul, 2015 ; Kim et al, 2016 ).…”

Water is a preservative of microbes

“…Ultraviolet radiation is sharply reduced with depth in a water column by dissolved organic compounds such as humic and fulvic acids, absorbance and scattering by particulates, and absorbance by water molecules themselves. By contrast, ultraviolet radiation is not strongly absorbed by dissolved salts such as NaCl and MgCl 2 (Godin et al ., 2020). Ultraviolet radiation with energies less than ~ 10 eV can cause electronic excitation resulting in O‐H bond cleavage of water, but ultraviolet photons with energies above ~ 10 eV may ionize water, leading to reactive species (Arumainayagam et al ., 2019).…”

Protective Effects of Halite to Vacuum and Vacuum-Ultraviolet Radiation: A Potential Scenario During a Young Sun Superflare

“…Halite forms as brines evaporate, and microorganisms living in these environments are naturally trapped within fluid inclusions inside these crystals (e.g., Norton and Grant, 1993). Moreover, crystals of halite, in particular, and crystals of salts, in general, may provide shielding against UV radiation (Fendrihan et al, 2009;Godin et al, 2020).…”