Detectability of targeted organics in mineral matrices by Raman spectroscopy in preparation for planetary exploration missions

Understanding the conditions of habitability and searching for evidence of life beyond Earth are key scientific goals of recent planetary exploration missions on Mars, such as the Mars 2020 and the ExoMars missions. These missions will characterise past aqueous environments of the planet and seek for potential biosignatures using planetary rovers capable of collecting rock samples and interrogating them using miniaturised analytical instrumentation. Raman spectrometers have been newly included into the scientific payload of planetary rovers for Mars exploration, owing to their ability to simultaneously detect inorganic and organic constituents from (bio)geological samples. However, detecting various mineral phases and possibly trace organics in powdered rocks and soils from Mars using miniaturised Raman systems is challenging and requires specific efforts in analytical chemistry. Therefore, as part of the present thesis, and in preparation of the missions, extensive research was dedicated to document the analytical capabilities of Raman spectrometers, including a mission-representative instrument tested under the technical constraints inherent with space missions, when analysing Mars relevant samples.
In this research project, we report on the characterisation of potential Mars analogue materials, such as hydrothermal fossil vents and various rock powder samples, including clay-rich geological samples. Furthermore, we present various analytical developments for Raman analyses on solid dispersions, in order to assess the influence of key Raman operating parameters (e.g. laser spot size, Raman subsampling) on the measured Raman spectral intensity for quantitative analysis purposes. Finally, quantitative models are developed using various Raman systems, including a miniaturised spectrometer, to quantify targeted organics dispersed within mineral matrices relevant to the geology of Mars. The detection of potential biomarkers by Raman with respect to the astrobiological exploration of Mars is eventually discussed.