Search

One of the objectives of the various space exploration missions carrying GC-MS (Gas chromatography coupled to mass spectrometry) instruments is the search for traces of life, in particular through the detection of biomolecules or bioindicators. This is for example the case of missions to Mars such as Mars Science laboratory and the SAM instrument but also the future ExoMars mission with the MOMA instrument. Up to date, we are looking for primary metabolites (such as fatty acids, amino acids or nucleobases) (Engel et al., 2001; Martins et al., 2008). Other organic molecules (produced by organisms) should also be considered for future space explorations of extant or present trace of life. More than 3.5 billion years ago, Mars had a similar weather and surface (in terms of geochemical composition, geodynamics, or resources necessary to define a planetary habitability (e.g. water, energy sources, complex organic molecules)) (Sterns et al., 2022; Raulin-Cerceau et al., 2004). Thus, the primordial soup necessary for the origin and evolution of life might be the same as on the Early-Earth. Therefore, if life exists or have existed on Mars, the primary cells produced on Mars might be similar to those found on Earth, and their (primary and secondary) metabolites might be identic. Based on this hypothesis, we have searched for biosignatures and bioindicators in extremophile cultures found in environmental Mars analogues, which may resist to the different stress measured on Mars (namely irradiation, salt matrices, low temperatures, water shortage, etc...): Chroococcidiopsis cubana and Halobacterium salinarum (Caiola et al., 2007; Ruginescu et al., 2019). To compare with a previous study conducted on these extremophiles with the TMAH thermochemolysis protocol, we conducted a parallel study with the two other wet chemistry protocols ahead the GC-MS analysis onboard the SAM , and the MOMA instruments, namely DMF-DMA and MTBSTFA derivatizations (Freissinet et al., 2010; Brault, 2016). The current study might help to understand which organic molecules are detectable with our space protocols and to construct a decisional tree for future in situ Mars results’ interpretations as it was a success analyzing ancient life fossils in Atacama desert (Crits-Cristopher et al., 2013; Santiago et al., 2018).

In 2015 the SAM experiment on board the curiosity rover discovered the first organic molecule endogenous to Mars. This molecule is certainly the result of the reaction of a still unknown molecule with the perchlorates/chlorates present in the Martian soil [1]. Since then, other organics have been discovered: sulfur and nitrogen bearing molecules [2-3] and chlorohydrocarbons [4]. Those chlorohydrocarbons compounds could be generated by a reaction which may occur at Mars’ near-surface induced by the harsh radiative environment, e.g. direct radiation (UV, high energy X- and γ-rays) and secondary photons produced by the interaction of direct radiations with the martian regolith (low energy secondary X-rays). Additionally, organic molecules are detected in lower concentration than expected from modelling [5], suggesting organic matter degradation over geological time. Our team thus investigates the influence of radiations on organic molecules under simulated Mars’ surface conditions. In the present study, we mainly focused on the action of X-rays (hard and soft X-ray) on various organic molecules, the chiral amino acids L-alanine and L-phenylalanine and two potential precursors of chlorobenzene, benzoic and trimesic acids. These molecules were irradiated pure but also in contact with calcium perchlorate in order to better understand the roles in perchlorates present in the Martian soil. We also studied the molecules within mineral matrices in the form of pellets, in absence and in presence of perchlorates (max 3 % weight).

In 2027 NASA will launch a new exobiological mission to Titan: Dragonfly [1,2]. Onboard the DraMS instrument will aim to map the organic compounds present on the surface of the satellite and to study the fate of this organic matter towards a potential prebiotic chemistry [3,4]. To do so, DraMS is equipped with a gas chromatography instrument coupled to a mass spectrometer (GC-MS). In order to be analyzed, the samples taken by the DrACO module will be placed in an oven which will allow the sample treatment. Different techniques of sample treatment can be used: pyrolysis, derivatization and thermochemolysis. Pyrolysis allows to volatilize efficiently the organic content of the sample but has the disadvantage of degrading the original content. The derivatization allows to avoid the degradation of the labile molecules while allowing their volatilization. This derivatization will be realized thanks to the use of DMF-DMA (dimethylformamide dimethylacetal) [5]. This reagent allows to keep the asymmetry centers of the labile molecules while volatilizing them and thus allowing the separation of their enantiomers on a chiral column of Chirasil-Dex type. The last technique, thermochemolysis, is dedicated to more refractory compounds. It combines both pyrolysis and derivatization techniques by using TMAH (tetramethylammonium hydroxide) or TMSH (trimethylsulfonium hydroxide) and temperatures of about 500°C [6].In order to optimize the treatment of DraMS samples, we studied the impact of each derivatization and thermochemolysis reagent on the identified organic targets (amino acids, nucleic bases, fatty acids, etc.) as well as using Titan analogues synthesized at LATMOS (UVSQ, France): Tholins [7].