Mineralogical effects on organic detectability via laser desorption mass spectrometry

The goals of current and future Mars missions include the search for biosignatures and the characterization of potentially habitable environments. Laser desorption mass spectrometry (LDMS) is capable of supporting Mars science objectives by analyzing a range of biosignatures and providing geological context for those measurements; hence the inclusion of an LDMS instrument on the ExoMars rover mission. However, LDMS techniques are sensitive to the host phase, and high-priority landings sites on Mars possess a wide range of minerals. This study explores how select minerals found on Mars, specifically those observed in Jezero crater and Oxia Planum, influence the detection of biosignatures via LDMS. Cholesterol was the target organic for this study due to its similarity to hopanoids, a class of bacterial lipids preserved in abundance in Earth's rock record. Seven Mars-relevant minerals were doped with a cholesterol-rich dilution series. This enabled the creation of calibration curves from which the limit of detection (LOD) of cholesterol adsorbed onto each mineral was determined. Of the minerals used in this study, lizardite facilitated the lowest cholesterol LOD at tens of ppmw while the other minerals had LODs up to hundreds of ppmw. Variables such as thermal conductivity, UV absorption, surface adsorption, and mineral chemistry were explored to explain the differences in LODs, but future work remains to identify the dominant influence. This work demonstrates the importance of geologic context for LDMS analyses and may be used for triaging returned samples for astrobiological studies and prioritizing targets during in-situ life detection missions.