Aqueous Processes and Microbial Habitability of Gale Crater Sediments from the Blunts Point to the Glenn Torridon Clay Unit

A driving factor for sending the Mars Science Laboratory, Curiosity rover to Gale Crater was the orbital detection of clay minerals in the Glen Torridon (GT) clay unit. Clay mineral detections in GT suggested a past aqueous environment that was habitable, and could contain organic evidence of past microbiology. The mission of the Sample Analysis at Mars (SAM) instrument onboard Curiosity was to detect organic evidence of past microbiology and to detect volatile bearing mineralogy that can inform on whether past geochemical conditions would have supported microbiological activity. The objective of this work was to 1) evaluate the depositional/alteration conditions of Blunts Point (BP) to GT sediments 2) search for evidence of organics, and 3) evaluate microbial habitability in the BP, Vera Rubin Ridge (VRR), and GT sedimentary rock

Organic chemistry in a CO₂ rich early Earth atmosphere

International audienceThe emergence of life on the Earth has required a prior organic chemistry leading to the formation of prebiotic molecules. The origin and the evolution of the organic matter on the early Earth is not yet firmly understood. Several hypothesis, possibly complementary, are considered. They can be divided in two categories: endogenous and exogenous sources. In this work we investigate the contribution of a specific endogenous source: the organic chemistry occurring in the ionosphere of the early Earth where the significant VUV contribution of the young Sun involved an efficient formation of reactive species. We address the issue whether this chemistry can lead to the formation of complex organic compounds with CO2 as only source of carbon in an early atmosphere made of N2, CO2 and H2, by mimicking experimentally this type of chemistry using a low pressure plasma reactor. By analyzing the gaseous phase composition, we strictly identified the formation of H2O, NH3, N2O and C2N2. The formation of a solid organic phase is also observed, confirming the possibility to trigger organic chemistry in the upper atmosphere of the early Earth. The identification of Nitrogen-bearing chemical functions in the solid highlights the possibility for an efficient ionospheric chemistry to provide prebiotic material on the early Earth

Performance of the SAM gas chromatographic columns under simulated flight operating conditions for the analysis of chlorohydrocarbons on Mars

"Multi-column gas chromatography analysis of chlorohydrocarbons 1with the SAM experiment onboard NASA’s Mars Curiosity rover" est le titre provisoire de la publication.International audienceThe Sample Analysis at Mars (SAM) instrument is a gas chromatograph-mass spectrometer onboard the NASA Curiosity rover, currently operating on the surface of Mars. Organic compounds are of major importance with regard to questions of habitability and the potential presence of life on Mars, and one of the mission’s main objectives is to analyze the organic content of soil and rock samples. In SAM’s first chromatographic measurements, however, unexpected chlorine-bearing organic molecules were detected. These molecules have different origins but the presence of perchlorates and chlorates detected at the surface of Mars suggests that reactivity between organic molecules and thermal decomposition products from oxychlorines is one of the major sources of the chlorinated organic molecules. Here we perform a comprehensive and systematic study of the separation of volatile chlorohydrocarbons with the chromatographic columns used in the SAM instrument. Despite the constrained operating conditions of the flight instrument, we demonstrate that SAM’s capillary chromatographic columns allow for effective separation and identification of a wide range of chlorine-bearing species. We also show that instrumental limitations prevent the detection of certain molecules, obscuring our ability to make definitive conclusions about the origin of these organic materials

In situ analysis of Mars soil and rocks samples with the SAM experiment: laboratory measurements supporting treatment and interpretation of the detection of organics

International audienceThe Sample Analysis at Mars (SAM) experiment onboard the Curiosity rover detected numerous organic compounds when analyzing the solid samples collected on the way to Mount Sharp. But MTBSTFA, the chemical reactant for the chemical treatment of the refractory molecules present in the solid samples and present in cups of SAM, was shown to be unfortunately present in the Sample Manipulation System (SMS). During the sample analysis, this chemical species reacts with the organic and inorganic molecules present in the samples. This reaction leads to the production and subsequent detection of numerous MTBSTFA derivatives which makes the treatment and the interpretation of the SAM data complex. Moreover, for the first time on Mars, the wet chemistry method was used on a Cumberland sample to help the GC separation and the MS identification of non volatile compounds. To ensure the identification of the organic molecules and try to discriminate organics generated internally to SAM from those present in the samples analyzed, it is mandatory to perform laboratory experimental calibrations under martian operating conditions

Influence of Calcium Perchlorate on Organics under SAM‐like Pyrolysis Conditions: Constraints on the Nature of Martian Organics

International audienceMost of the organics detected on Mars so far are aliphatic and aromatic organo‐chlorine compounds. The smallest were first identified by the thermal treatment of the solid samples by Viking in 1976, although at the time, they were attributed to contamination. Since 2012, a larger variety of structures have been identified by the Sample Analysis at Mars (SAM) experiment aboard the Curiosity rover. Evidence suggests that the chlorohydrocarbons formed during pyrolysis of sedimentary materials. Laboratory experiments show that heating of samples containing oxychlorines, such as chlorates (ClO3‐) and perchlorates (ClO4‐), along with organic matter present at Mars’ surface is the logical source of these compounds. Nevertheless, this discovery of indigenous organic matter in the Mars regolith raises important questions: How do the oxychlorines influence the pyrolysis of organics? What are the organics precursors of the organo‐chlorinated molecules detected on Mars? Is there a way to identify the parent molecules in a sample after pyrolysis? This paper presents the results of systematic laboratory experiments of the products formed during the pyrolysis of organic compounds from three chemical families—polycyclic aromatic hydrocarbons (PAHs), amino acids and carboxylic acids—in presence of calcium perchlorates. Results show that the PAH parent molecules and most of the carboxylic acids are still detectable after pyrolysis in presence of calcium perchlorate and that the degradation and/or evolution of all parent molecules mostly depends on their chemical nature. In addition, we demonstrate that the chlorohydrocarbons detected on Mars by the SAM instrument could come from the three chemical families studied

Influence of pH and salts on DMF-DMA derivatization for future Space Applications

International audienceFor gas chromatography - mass spectrometry (GC-MS) analyses performed in situ, pH and salts (e.g., chlorides, sulfates) may enhance or inhibit the detection of targeted molecules of interest for astrobiology (e.g. amino acids, fatty acids, nucleobases). Obviously, salts influence the ionic strength of the solutions, the pH value, and the salting effect. But the presence of salts may also produce complexes or mask ions in the sample (masking effect on hydroxide ion, ammonia, etc.). For future space missions, wet chemistry will be conducted before GC-MS analyses to detect the full organic content of a sample. The defined organic targets for space GC-MS instrument requirements are generally strongly polar or refractory organic compounds, such as amino acids playing a role in the protein production and metabolism regulations for life on Earth, nucleobases essential for DNA and RNA formation and mutation, and fatty acids that composed most of the eukaryote and prokaryote membranes on Earth and resist to environmental stress long enough to still be observed on Mars or ocean worlds in geological well-preserved records. The wet-chemistry chemical treatment consists of reacting an organic reagent with the sample to extract and volatilize polar or refractory organic molecules (i.e. dimethylformamide dimethyl acetal (DMF-DMA) in this study). DMF-DMA derivatizes functional groups with labile H in organics, without modifying their chiral conformation. The influence of pH and salt concentration of extraterrestrial materials on the DMF-DMA derivatization remains understudied. In this research, we studied the influence of different salts and pHs on the derivatization of organic molecules of astrobiological interest with DMF-DMA, such as amino acids, carboxylic acids, and nucleobases. Results show that salts and pH influence the derivatization yield, and that their effect depend on the nature of the organics and the salts studied. Second, monovalent salts lead to a higher or similar organic recovery compared to divalent salts regardless of pH below 8. However, a pH above 8 inhibits the DMF-DMA derivatization influencing the carboxylic acid function to become an anionic group without labile H. Overall, considering the negative effect of the salts on the detection of organic molecules, future space missions may have to consider a desalting step prior to derivatization and GC-MS analyses

The application of TMAH thermochemolysis on the detection of nucleotides: applications for the SAM and MOMA space experiments

International audienceThe Sample Analysis at Mars (SAM) instrument onboard the Curiosity rover and Mars Organic Molecule Analyzer (MOMA) instrument onboard the ExoMars rover are two of the most important instruments used for the in-situ search for biosignatures of life on Mars. Tetramethylammonium hydroxide (TMAH) thermochemolysis combined with pyrolysis-gas chromatography and mass spectrometry (Py-GC/MS) has been one of the main techniques utilized by SAM and will be utilized by MOMA. They are both capable of detecting molecular fragments and patterns indicative of life in the Martian near-surface. This study identifies the TMAH thermochemolysis products of targeted nucleotides using flash pyrolysis and SAM-like ramp pyrolysis experiments. Additionally, the optimal TMAH thermochemolysis temperature was determined. Results indicate that the methylated nucleosides can be detected at low abundances when exposed to TMAH thermochemolysis flash pyrolysis at 200 °C. Notably, higher pyrolysis temperatures led to the degradation of nucleosides. Furfuryl methyl ether, one of the degradation products of these nucleosides, was also identified from 200 to 600 °C in this study. 300 °C is the optimal temperature for the detection of methylated phosphate under flash pyrolysis of the tested nucleotides with TMAH thermochemolysis. Methylated nucleobases, methyl furfuryl and methyl phosphate are the main products of the tested nucleotides under SAM-like ramp thermochemolysis. Ramped thermochemolysis also resulted in improved performance over flash pyrolysis in the detection of characteristic nucleotide compounds. Uracil and thymine can be detected by both SAM and MOMA if there are nucleotides on Mars; additionally, MOMA will be able to detect adenine. Therefore, methyl furfuryl, methylated phosphate, and the methylated nucleobases uracil, thymine, and adenine are the organic compounds that should be within the SAM and MOMA detection windows if there is DNA/RNA conserved in Martian soil. These experiments will provide a reference for the data collected in-situ by the Curiosity rover and the future ExoMars rover