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Communication Dans Un Congrès Année : 2021

Results from the TMAH Wet Chemistry Experiment on the Sample Analysis at Mars (SAM) Instrument Onboard NASA's Curiosity Rover

Résumé

The Mars Curiosity rover carries a diverse instrument payload to characterize habitable environments in the sedimentary layers of Aeolis Mons (Mt. Sharp) in Gale crater. One of these instruments is Sample Analysis at Mars (SAM), which includes a tunable laser spectrometer, quadrupole mass spectrometer, gas chromatograph, and the capability to perform wet chemistry (derivatization and thermochemolysis) analyses with pyrolysis gas chromatography mass spectrometry (py-GC-MS). The SAM sample carousel contains 74 individual sample cups housed within two concentric rings of the carousel. Nine of these cups are slated for wet chemistry experiments and contain reagents for either thermochemolysis (two cups with tetramethylammonium hydroxide [TMAH] in methanol) or derivatization (seven cups with N-methyl-N-tertbutyldimethylsilyl-trifluoroacetamide [MTBSTFA] in dimethylformamide). Wet chemistry experiments aim to transform polar organic molecules (e.g., carboxylic or amino acids) into volatile derivatives that are amenable and detectable by GC-MS as well as freeing bound components of larger macromolecules otherwise undetectable with GC-MS. TMAH thermochemolysis can liberate fatty acids bound in macromolecules or chemically bound monomers associated with mineral phases and make these organics detectable via GC-MS by methylation. Fatty acids are of interest given their presence in both biotic and abiotic materials. They are ubiquitous and abundant constituents of bacterial and eukaryotic cellular membranes, bound in phospholipids and glycolipids. Carboxylic acids have also been identified in exogenous carbonaceous material, for example having been detected in the Murchison meteorite. Full cup and opportunistic derivatization MTBSTFA experiments have been performed on Mars and have yielded interesting results including the potential detection of C10 and C12 alkanes and other derivatized molecules, the origin of which are still being investigated. The first TMAH experiment is anticipated in 2020 in the Glen Torridon (clay-bearing) unit. TMAH experiments with samples analogous to the Glen Torridon unit have demonstrated that fatty acids, if well preserved or recently present (<2 Ga), are detectable with a benchtop version of the SAM TMAH experiment. The detection of a fatty acid profile is of great astrobiological interest, as it could provide information regarding the source of Martian organic material. Biotic fatty acids derived from terrestrial cellular membranes have an even-over-odd carbon chain length preference reflecting biochemical additions of acyl (C2) monomer, whereas abiotic carboxylic acids often favor shorter carbon chain lengths and show no carbon number preference due to single-carbon-addition reactions. The TMAH experiment presents the first opportunity to detect organic molecules bound in macromolecules on Mars with thermochemolysis. Optimization of this experiment on SAM will feed forward to future missions, as a version of the TMAH experiment is also present in the Mars Organic Molecule Analyzer (MOMA) instrument onboard the ESA ExoMars rover.
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Dates et versions

insu-04473669 , version 1 (22-02-2024)

Identifiants

Citer

Amy Williams, Rafael Navarro-Gonzalez, Arnaud Buch, Daniel Glavin, Caroline Freissinet, et al.. Results from the TMAH Wet Chemistry Experiment on the Sample Analysis at Mars (SAM) Instrument Onboard NASA's Curiosity Rover. 43rd COSPAR Scientific Assembly, Jan 2021, Sydney, Australia. pp.Abstract F3.3-0003-21 (oral), id.1939. ⟨insu-04473669⟩
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