Sample Chemistry Revealed by TMAH-Evolved Gas Analysis: Results from the First In Situ Thermochemolysis Experiment at Gale Crater, Mars

The Sample Analysis at Mars (SAM) instrument suite on the NASA Curiosity rover in Gale crater, Mars has the capability to conduct wet chemistry experiments, including two thermochemolysis experiments. In these experiments, 50-150 mg of sedimentary samples bearing diverse minerals and chemical compositions, including possible organic materials, will be saturated with 500 microliters of 25% tetramethylammonium hydroxide [TMAH] in methanol. Upon heating this mixture, the alkaline reagent methylates amenable functional groups (via hydrolysis of -OH, -O-, -NH, and -SH groups followed by methylation) to produce volatile products that are directly analyzed by the mass spectrometer (evolved gas analysis, EGA) or trapped and analyzed with gas chromatography mass spectrometry (GC-MS). Importantly, the TMAH reagent is corrosive to silicates with active -OH sites and releases organic components bound to both other organics (within macromolecules) or minerals. Together, these actions have the potential to release diverse inorganic and organic chemicals from sedimentary samples that are not observable by other SAM experiments. The search for long-chained carboxylic acids is enabled by this experiment (see Williams et al., this meeting). There is also the potential for a unique and more diverse organic chemistry to be revealed that may shed light on organic chemical sources, preservation mechanisms and degradation processes. In particular, functionalized aromatics and small organic acids, which were observed in other SAM experiments and are possible radiolysis/oxidation products of ancient deposited sedimentary organics, may be detected in greater abundance. Current Mars Science Laboratory (MSL) mission's SAM results will inform future Mars Organic Molecular Analyzer (MOMA) analyses involving TMAH thermochemolysis of 3.9-billion-years-old, clay-rich samples collected by the 2022 ExoMars rover from the surface to 2-meters depth in the Oxia Planum region. This report will focus on the evolved gas analysis associated with the first TMAH thermochemolysis experiment (to be conducted on Mars in 2020) on a phyllosilicate-bearing sedimentary sample from the Glen Torridon region. Results will be compared to other SAM experiments and include related GCMS observations.