Biomass and habitability potential of clay minerals- and iron-rich environments: Testing novel analogs for Mars Science Laboratory landing sites candidates

The landing site of the next mission to Mars (the US 2011 Mars Science Laboratory) will include phyllosilicate outcrops as targets for investigating the geological and biological history of the planet. In this context, we present a preliminary study assessing the living biomass and habitability potential in mineralogical Mars analogs by means of multi-component investigations (X-ray diffraction, microRaman spectroscopy and SEM\EDX). Phyllosilicate and hematite-rich deposits from the Atacama Desert (Chile), Death Valley (CA), and the California Coast, encompassing a broad arid to hyper-arid climate range (annual rainfall 0.2 to 700 mm/year), were analyzed for total and viable Gram-negative biomass, i.e. adenosine 5'-triphosphate (ATP) and Limulus amebocyte lysate (LAL) assays. Basic observations were: (1) there is no systematic pattern in biomass content of clay-rich versus non-clay (oxidized) materials; (2) Atacama desiccation polygons (6.0 x 104 cells/g) and contiguous hematite-rich deposits contain the lowest biomass (1.2 x 105 cells/g), which is even lower than that of coarse-grained soil nearby (3.3-5.0 x 105 cells/g); (3) the Atacama clay-rich samples (illite-muscovite and kaolinite) are three orders of magnitude lower than surface clay (montmorillonite, illite, and chlorite) from Death Valley; and (4) finally, and unexpectedly, the Gram-negative content (6.4 x 107 cells/g) of clay mineral-rich materials from the arid Death Valley region is up to six times higher than that (1.5 to 3.0 x 107 cells/g) of water-saturated massive clays (kaolinite, illite and montmorillonite) from the California Coast (wetter end-member). MicroRaman spectroscopy investigation on a Death Valley sample indicates that gypsum (1008, 618, and 414 cm-1 Raman shift), and inferred associated organic (scytonemin) biosignatures (1281 cm-1) for the measured Gram-negatives (cyanobacteria) were successfully captured.