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Characteristic geological features and hydrated minerals recently found on the surface of Mars by the NASA planetary rovers Spirit and Opportunity suggest that a possible biosphere centered around liquid water could have once existed there. Analytical instrumentation protocols for the unequivocal detection of biomarkers in suitable geological matrices are critical for future unmanned explorations, including the forthcoming ESA ExoMars mission scheduled for 2018.
Raman spectroscopy is currently a part of the Pasteur instrumentation suite of the ExoMars mission for the remote detection of extant or extinct life signatures in the Martian surface and subsurface. Terrestrial analogues of Martian sites have been identified and the biogeological modifications incurred as a result of extremophilic survival activity in stressed environments have been studied. Polyaromatic hydrocarbons (PAHs) are recognized as a class of degradation product that can occur terrestrially from biological processes.
Here, we present the Raman spectral characterization of several examples of PAHs alone and in admixture with other species in geological matrices. Experimental mixtures of anthracene, pyrene and perylene in matrices of gypsum, calcite and quartz in 50-50 concentrations have been investigated by Raman microspectrometry in simulation of their potential identification in geobiological conditions in Martian scenarios. The pure compounds and compound mixtures were also analysed using X-ray powder diffraction.