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.