Absorption and Scattering of UV and Visible Light Through Simulated Martian Regoliths and Rock Samples.

Ultraviolet shielding materials are potential ecological niches for biosignatures. Finding such materials on Mars would narrow the search for potentially habitable regions. A mini-goniometer was built to collect transmission spectra as a function of scattering angle for Mars analog regoliths (JSC Mars-1, basalt, cheto bentonite, and kieserite) and crystalline rock samples from the Haughton impact structure on Devon Island, Nunavut, in the Canadian High Arctic Archipelago. The transmission through the materials was assessed at ultraviolet and visible wavelengths and at different scattering angles. From the results, it is possible to classify the samples into UV transmitters and UV quenchers. UV transmitters are materials that favor transmittance of UV wavelengths compared to photosynthetically active radiation (PAR), while the UV quenchers are materials that effectively block UV radiation from propagating into the subsurface. Additionally, samples that are effective UV quenchers tend to have more isotropic scattering profiles, whereas UV transmitters tend to favor forward scattering profiles. Samples with greater porosity had greater overall transmission. The depths at which radioresistant microorganisms can exist on present-day Mars are estimated by modeling the transmission for regoliths and crystalline rocks under martian insolation. The depth at which LD90 occurs is found to range down to 0.3 mm, while still allowing up to 1000 kJ/m2 of PAR at those depths. Due to the exceptionally protective nature of JSC Mars-1, intimate mixtures of organisms and regolith will result in some organisms experiencing orders of magnitude less UV flux than others, even when protected by only a single grain of simulant.

Salt Tolerance and UV Protection of Bacillus subtilis and Enterococcus faecalis under Simulated Martian Conditions.

Ultraviolet (UV) irradiation on the surface of Mars is an important factor that affects the survivability of microorganisms on Mars. The possibility of martian brines made from Fe2(SO4)3, MnSO4, and MgSO4 salts providing a habitable niche on Mars via attenuation of UV radiation was investigated on the bacteria Bacillus subtilis and Enterococcus faecalis. Results demonstrate that it is possible for brines containing Fe2(SO4)3 on Mars to provide protection from harmful UV irradiation, even at concentrations as low as 0.5%. Brines made from MnSO4 and MgSO4 did not provide significant UV protection, and most spores/cells died over the course of short-term experiments. However, Fe2(SO4)3 brines are strongly acidic and thus were lethal to E. faecalis, when cells were exposed for 7 days. In contrast, B. subtilis, a spore-forming bacterium resistant to pH extremes, was unaffected by the acidic conditions of the brines and did not experience any significant lethal effects in Fe2(SO4)3. Any extant microbial life in martian Fe2(SO4)3 brines (if present) would need to be capable of surviving acidic environments, if these brines are to be considered a possible habitable niche. The results from this work are important to the search for life on planets with atmospheres that do not significantly attenuate UV radiation (i.e., like Mars) and to planetary protection, since it is possible that terrestrial bacteria in the genus Bacillus are likely to survive in Fe-sulfate brines on Mars.