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Search for organic molecules on the surface of Mars : influence of the cation on the analysis of aromatic acids salts with gas chromatography-mass spectrometry and implications for Mars

Presentation #108.07 in the session Astrobiology and Origins of Life (Oral Presentation)

Published onOct 23, 2023
Search for organic molecules on the surface of Mars : influence of the cation on the analysis of aromatic acids salts with gas chromatography-mass spectrometry and implications for Mars

The harsh oxidative and radiative conditions at the surface of Mars influence the fate of organic molecules that can be present in this environment. Aromatic carboxylic acids, such as phthalic acid or benzoic acid, are thought to be potential abundant organic species in the soil because they are in stable intermediate oxidation states and can be formed from the oxidation of Mono or Polycyclic Aromatic Hydrocarbons (PAHs) coming from endogenous or exogenous sources. Benner et al. (1) suggested that the low volatility of these salts could compromise their in situ detection through thermal extraction analyses as performed by analytic chemistry laboratories onboard past, present, and future Martian surface probes. However, no extended study was ever published considering the different conditions of thermal extraction that can be used, or the nature of the cation present in the salt.

This is the reason why our team performed gas chromatography-mass spectrometry analyses in the laboratory, of various aromatic acid salts bearing different cations, compatible with the elements present at the Mars surface, in order to assess the influence of the cation on the analysis. The extraction of the molecules from the test samples was done using pyrolysis, derivatization, and thermochemolysis in conditions aiming to reproduce those used, or to be used, by the three analytical laboratory dedicated to search for organic molecules on the Mars surface, i.e. the Gas Chromatograph-Mass Spectrometer (GC-MS) experiment onboard the Viking probes, the Sample Analyzer at Mars (SAM) experiment onboard the Curiosity rover, and the Mars Organic Molecular Analyzer (MOMA) instrument of the Rosalind Franklin Exomars rover (2-4).

The main objective is to determine the possibility to identify in situ the organic salts tested through their direct or indirect detection using the chemical species they produce when submitted to the different sample preparation treatment. This communication aims to present extensively the results obtained with the different cations and the different sample preparation conditions considered, and to discuss the detectability of these aromatic organic salts in situ.

References. (1) S. A. Benner et al., PNAS 97, 2425-2430 (2000). (2) K. Biemann et al., 82, 4641-4658 (1977). (3) P. Mahaffy et al., Space Science Reviews 170, 401-478 (2012). (4) F. Goesmann et al., Astrobiology 17, 655-685 (2017).

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