Surface mineral crusts: a potential strategy for sampling for evidence of life on Mars

Surface mineral crusts on Earth are highly diverse and usually, contain microbial life. Crusts constitute an attractive target to search for life: they require water for their formation, they efficiently entrap organic matter and are relatively easy to sample and process. They hold a record of life in the form of microbial remains, biomolecules and carbon isotope composition. A miniaturized Raman spectrometer is included in the ExoMars 2020 payload as it is sensitive to a range of photosynthetic pigments. Samples from the Haughton Impact Structure, Canadian High Arctic and others, shows the preservation of pigments in a range of crust types, especially supra-permafrost carbonate crusts and cryptogamic crusts. The Raman spectral signatures of these crusts are shown along with biomarker analysis to showcase these techniques prior to the ExoMars 2020 mission. Carotenoids and other photoprotective microbial pigments are identified in the Haughton surface crusts using Raman spectroscopy. Gas chromatography-mass spectrometry analyses show a distribution of fatty acids which are most likely from a cyanobacterial source. The successful demonstration of these analyses in the Haughton Impact structure shows the biosignature of surface mineral crusts can be easily extracted and provides an excellent target for sampling evidence of life on Mars.