Raman Estimation of Olivine Forsterite-Fayalite Ratio: Laboratory Analysis to Refine the Interpretation of Supercam Detections on Mars

The SuperCam instrument onboard the Mars2020 Perseverance rover is a multi-analytical instrument including LIBS, Raman and VISIR spectroscopy in addition to a microphone. During the Mars2020 Crater Floor campaign, SuperCam achieved the unequivocal Raman detection of olivines on the Jezero Crater in Mars. Knowing that prediction models can be used to estimate the Mg/Fe ratio of olivine crystals from the position of their Raman doublet, this work seeks to determine the applicability of these models to SuperCam spectra, as well as to assess the level of uncertainty of their predictions. Using synthetic olivine as testing samples, it was experimentally proved that prediction models based on the analysis of band DB1 (around 820cm-1) are not suitable for the interpretation of SuperCam Raman spectra. This is due to a contribution of multiple factors affecting the position

of the band, including the selected excitation wavelength, the low signal to noise ratio (SNR) of Martian spectra, and the influence of band fitting procedure and minor cationic substitutions of Fe for Mn. As for prediction models based on DB2 (850cm-1), the one proposed by Kuebler et al. ensured the highest reliability of results. During the conference, a summary of the olivine detections by SuperCam Raman will be presented. Furthermore, the application of Kuebler's method to Raman data collected from Garde and Dourbes abraded patches on the Séitáh region on the Jezero crater will be discussed, showing how this method suggests a Fosteritic (Fo) content between 59 and 63, in full agreement with the semi-quantitative results provided by complementary techniques (XRF and LIBS) onboard the Perseverance rover. Finally, potential solutions to further optimize the reliability of Raman predictions will be discussed as part of this work.