Astrobiological Assay Validation across Gradients in Mars Analogue Sites: Lessons from the FELDSPAR Project

Recent basaltic eruption sites in Iceland are considered Mars analogues for surface mineralogy, constrained bioavailable chemistry, very low biomass, and (in some cases) water/ice activity. Such sites also contain temperature, moisture, and geochemical gradients, both due to geochemical activity and to topology. Correlating remote imagery, surface mineralogy, and biomarker assay results across such gradients will help optimize Mars sample site selection for likely biomarker distribution and preservation.

The FELDSPAR team's most recent expeditions (2017 and 2018) to Icelandic Mars analogue sites tested a battery of physicochemical measurements and biomarker assays along transects including layered deposits, temperature, alteration, oxidation, wind and solar exposure, slope changes, and grain size sorting. Here we report intermediate results.

Sites were Holuhraun and Dyngjusandur, both geologically recent basaltic lava flows. (Other sites were sampled as part of the overall FELDSPAR project, but did not target gradients.) VIS/NIR reflectance and XRF spectra were taken for mineralogical classification, along with temperature measurements and other field observations. Biomarker assays were ATP quantification (performed in a temporary field lab), qPCR, and some DNA sequencing; these targets were chosen as proxies for different classes of potential Mars biomarker types (biomass, bioavailable energy, etc.).

The performance of the ATP assay in the differing geochemical types sampled was validated using standard addition. Results indicate that the assay yielded usable results in all types of samples tested, although many highly oxidized or hot sample sites indicated a level below the lowest detectable limit. DNA was extracted from all 2017 samples; 2018 sample processing is still underway. Spectroscopy initially proved challenging due to the very dark color and low ambient light at Dyngjusandur, but a near-complete set of reflectance and XRF spectra were obtained at Holuhraun and used to derive summary parameters analagous to the CRISM instrument.

Environmental monitoring devices were installed at a subset of 2018 sample sites to obtain additional information on diurnal and seasonal exposure, for collection during the planned 2019 expedition.