Optimization of the Sample Analysis at Mars Wet Chemistry Experiment for the Detection of Organics in Glen Torridon

As Curiosity ascends Mount Sharp, the Sample Analysis at Mars (SAM) instrument—a pyrolyzer coupled to a gas chromatograph-mass spectrometer (pyro-GCMS)—continues to search organic molecules as clues for habitability. SAM performs in situ molecular analysis of gases evolved from heating solid samples collected by Curiosity, and carries two derivatization reagents to expand the range of organics that can be detected. The N-methyl-N-(tert-butyldimethylsilyl) trifluoroacetamide (MTBSTFA) reagent reacts with molecules of astrobiological interest while preventing their degradation. The first full cup MTBSTFA derivatization experiment was performed on the Ogunquit Beach (OG) sand sample from the Bagnold dune field. GCMS results showed the detection of derivatized benzoic acid as well as excess, unreacted MTBSTFA. However, no amino acids or fatty acids were detected.

Following these results, laboratory experiments were conducted to improve SAM's detection of derivatized organics. Mixtures of organic compounds expected on Mars (e.g. amino acids) were analyzed under SAM-like operating conditions. Results showed that by measuring the signal of compounds that continue to elute while the column cools down, we extend the effective range of heavy molecules that can be detected in the future.

Curiosity is now exploring Glen Torridon—the 'Clay-Bearing Unit'—and the SAM team is preparing the next set of experiments. Laboratory experiments on terrestrial clay minerals suggest they have a strong preservation potential of organic molecules, thus representing a key target lithology for SAM. The GCMS analysis of "Kilmarie," the first drill sample from Glen Torridon, did not show direct evidence of indigenous organics but the EGA detection of CO₂ and CO suggests oxalate decomposition or organic oxidation products. No wet chemistry analysis was performed on this sample. Curiosity is ready to drill another sample in a new area and SAM analysis will follow. If the organic content is promising, an optimized MTBSTFA derivatization experiment will be performed as well as the first TMAH experiment to be done on Mars. SAM-like derivatization experiments in laboratory on synthetized clay analogs minerals are ongoing to improve the flight parameters and the detection of derivatized organic molecules at Glen Torridon.