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The Mars 2020 and ExoMars 2022, rover-based missions are specifically dedicated to the search for evidence of life and will both utilise Raman spectrometers on the surface of Mars. Raman spectroscopy is indeed a valuable analytical technique for planetary exploration that enables in situ characterisation of rocks and soils collected directly from the surface or retrieved as cores and subsequently crushed when extracted from the subsurface with a drill. On Mars, the miniaturised spectrometers will interrogate ancient geological deposits, in order to try and identify hydrated or aqueously altered minerals and organic matter to assess the habitability of Mars. While the identification of relevant hydrous minerals and organic components is the primary analytical objective of the missions, quantifying their abundances would be of particular significance for interpreting past geological conditions (e.g. formation or alteration processes) and for ascertaining the putative presence of biosignatures. Therefore, we have developed quantitative models that enable the quantification of both mineral proportions from crushed mixtures of geological components and spiked mixtures containing organic analytes dispersed in mineral matrices. Based on data normalisation with appropriate standards (internal and external), we demonstrate that robust quantitative models can be (1) applied for solid dispersions of various complexities relevant to planetary exploration; and (2) applied to different Raman set-ups, including an instrument representative of the ExoMars Raman Laser Spectrometer. With important Raman-active minerals (calcite, gypsum, baryte, quartz), we demonstrate that using a correction factor Fφ2/φ1, based on the ratio of apparent Raman scattering coefficients, the relative proportion of minerals in binary mixtures can be accurately determined. Regarding the organics, evaluated in clay-rich sediments (Fe-smectite) and crushed rocks of coarse-grained fraction (>100μm), we establish calibration curves in the concentration range 2–20 wt% for non-resonant compounds (L -cysteine, phthalic acid, adenine) and even lower (<1 wt%) for pre-resonant anthracene. Despite large levels of heterogeneity, the Raman analyses of these solid dispersions verify that quantitative Raman analyses can be performed in the context of robotic exploration studies. [ABSTRACT FROM AUTHOR]

Two rovers will be launched in 2020 for robotic exploration missions on Mars: the ESA/Roscosmos ExoMars and the NASA Mars 2020 missions. Both missions will include Raman instruments to characterize the habitable of Mars and to search for molecular evidence of past and present life. In preparation for these missions and to characterize the scientific information that will eventually return from Mars, terrestrial analogue samples of rock formations on Mars are studied in detail. During this study, we compared Raman spectra obtained from different samples of geological matrixes, including specimens of silicate, sulfate, carbonates, and sulfurs, with two Raman instruments. Raman data were obtained in the field with a portable instrument operating with a 785‐nm laser. Based on fast data analyses in the field, a selection of samples were collected and were further analyzed using a benchtop confocal instrument operated in the laboratory and with two excitation lasers at 532 and 785 nm. We illustrate the possible interference from sharp fluorescence associated with rare earth element present in trace amount in minerals. In addition, carbonaceous compounds and β‐carotene, a highly Raman‐active biomarker, were also detected by Raman spectroscopy in association with specific minerals. In the context of planetary exploration, we discuss the capacity for specific mineral matrixes to sustain life under extreme conditions. We also discuss that Raman imaging, although not ready yet for space application with miniaturized spectroscopy, could significantly help in discussing the possible biotic origin of carbonaceous residues, especially by the association of molecular signatures with the localized microstructure. [ABSTRACT FROM AUTHOR]