Recherche d'indices de vie sur Mars :<br />détermination de signatures spécifiques de biominéraux et étude expérimentale de l'évolution de molécules organiques dans des conditions environnementales martiennes

The essential conditions of a terrestrial life emergence have been present at the beginning of Mars' story. Therefore, Martian life forms could have appeared and their clues could have perpetuated. In the purpose of searching for those clues, our work took into consideration two targets of exobiological interest: the carbonated biominerals and the organic matter. In the first part, we have suggested the possibility that the thermal resistance temperatures of biotic and abiotic carbonates differ due to their intrinsic characteristics. We have compared them with DTA-TG thermal analysis and we have observed a difference of 15°C between the biological and abiotic domains. Hence, we have access to a non-equivocal biological signature. In the second part, we have tested the photostability and the evolution of carboxylic acids and a bacterial biomarker, exposed to the solar simulated UV radiations on Mars surface. To do so, we have developed a laboratory simulation experiment: M.O.M.I.E (Martian Organic Molecules Irradiation and Evolution). We have observed that the majority of the organic molecules have been destroyed. Only the mellitic acid produces one or further resistant organics. We have thus access to the organic matter rates, potentially present on the Mars surface/subsurface. Those two followed research orientations are therefore of great exobiological interest because they enable us to define the future experimental strategies in order to detect in situ a possible Martian biological activity.Les conditions indispensables à l'émergence de la vie terrestre ont surement été réunies sur Mars au début de son histoire. Une forme de vie martienne aurait alors pu apparaître et des indices de cette dernière auraient pu perdurer. Dans le cadre de la recherche de ces indices sur Mars, nos travaux s'articulent autour de deux cibles d'intérêt exobiologique : les biominéraux carbonatés et la matière organique. Dans la première partie, nous avons fait l'hypothèse que les températures de résistance thermique de carbonates biogéniques et abiotiques diffèrent du fait de leurs particularités intrinsèques. Nous les avons comparées via des analyses thermiques TG-ATD et nous avons constaté qu'un écart de 15°C sépare les domaines biologiques et abiotiques. Par conséquent nous avons ainsi accès à une signature biologique non ambiguë. Dans la seconde partie, nous avons testé la photostabilité et l'évolution d'acides carboxyliques et d'un biomarqueur bactérien, soumis au rayonnement ultraviolet simulé du soleil à la surface de Mars. Pour cela, nous avons développé une expérience de simulation en laboratoire : M.O.M.I.E. (Martian Organic Molecules Irradiation and Evolution). Nous avons observé que la plupart des molécules organiques sont détruites. Une seule, l'acide mélitique, produit un ou des composés organiques résistants. Nous avons ainsi accès aux taux de matière organique potentiellement présent à la surface/sous-surface de Mars. Les deux axes de recherche que nous avons suivis sont donc d'un grand intérêt exobiologique, car ils nous permettent de définir les stratégies expérimentales à mettre en oeuvre pour tenter de détecter in situ une activité biologique martienne

Recherche d'indices de la vie sur Mars (détermination de signatures spécifiques de biominéraux et étude expérimentale de l'évolution de molécules organiques dans des conditions environnementales martiennes)

PARIS7-Bibliothèque centrale (751132105) / SudocSudocFranceF

The search for organic matter on Mars: evolution of nucleobases under Martian simulated environment

International audienceMars has always been a planet of interest. After several decades of exploration and the discovery of evidence that water may have been present in the liquid state during the first hundred million years of its history, the question of the habitability of this planet is still opened. According to our knowledge about terrestrial Life, it appears that Life is possible only with the presence of organic matter, liquid water and energy sources in order to activate the organic chemistry leading to one or several prebiotic chemistries before any biological activity. Organic matter on Mars may come from different origins such as an exogenous source (comets, meteorites…) or endogenous source (biological activity, atmospheric production…). However, only few organic molecules have been detected so far in the Martian regolith (chlorinated, sulphured molecules and methane). Yet, those molecules do not represent at least the exogenous source that is proven to reach the surface of Mars. One hypothesis is that organic matter evolves in the Martian environment, i.e. strong oxidative reactivity of the Martian regolith, UV radiation, X-rays… In order to understand the evolution of organic matter on the surface of Mars, we developed a setup reproducing some key parameters of Mars. This setup called MOMIE (Martian Organic Matter Irradiation and Evolution) aim to estimate qualitatively and quantitatively the evolution of organic molecules under the physical and chemical conditions of the surface of Mars. Initially, the MOMIE project consisted to follow the evolution of organic matter under a Mars-like simulated UV radiation. More recently, serious attention is being paid not only on the synergy of these radiations with oxidative compound such as perchlorates that have been detected on Mars, but also on the evolution initiated by other radiation such as X-rays. The aim is to test some organic molecules supposed to be present on Mars from at least the interplanetary medium. Among them, we choose to study nucleobases such as cytosine and hypoxanthine that have been proven to be UV-light resistant. The purpose of this work is to determine if those UV-light resistant molecules can resist to the X-rays and to the presence of perchlorate. If not, be able to calculate some kinetics constants and find out potential products of these evolutions. Identifying the products could be useful for future space missions in order to search for those molecules and their degradation products in the Martian regolith. The first results will be presented in the form of a poster

Study of the Evolution of Nucleobases Under Mars-Like Conditions: Impact of Uv-Irradiation and Perchlorates on Uracil and Cytosine.

International audienceThe search for organic molecules is one of the main goals of current and future Martian space missions. Many sources of organic molecules may exist at the surface of this planet: exogenous sources, such as the interplanetary medium, and/or endogenous sources, like hydrothermalism or a potential biological activity. However, only a few organics have been detected so far [1, 2] and their relation to any endogenous sources or to the compounds that are brought to the surface by interplanetary bodies is not straightforward. [3, 4, 5]. An explanation is that organic molecules are not well preserved in the Mars surface environment. This envi-ronment is characterized by different parameters i.e strong oxidants (perchlorates, iron oxides…), energetic radiation (UV, X-rays…) that could degrade or alter the organic matter. Therefore, the study of the possible actions of these harsh conditions on organic molecules is of high interest for the quest of organics on Mars, and this is the objective of the present work. Perchlorates have been detected in the Martian rego-lith, (0.4-0.6% by weight) [6, 7]. They are strong oxidants (containing ClO4- ions) and could react with organics [8] especially when they are activated by energetic sources, such as X-rays and UV light. This could explain why it is so hard to detect organics on the surface and near-surface of Mars. It could also possibly be a source of the chlorohydrocarbons detect-ed with the SAM experiment in gale crater [1]. This is the reason why we started studying the possible inter-action between UV radiation reaching the surface of Mars with organic molecules of high interest for astrobiology. The MOMIE (Mars Organic Matter Irradiation and Evolution) experiment is designed to study the evolution of organic molecules in a simulated Martian environment with respect to temperature, pressure and UV radiation. In the context of prebiotic chemistry, nucleobases are organic molecules of interest. Furthermore, some nucleobases were detected in meteorites [10] and were therefore brought to the surface of Mars at some point. Finally some of them are UV resistant or produce UV resistant photoproducts under Mars-like conditions [9]. To investigate the effect of perchlorates on nuclaobases and their UV photoproducts on Mars, we studied nucleobases with the MOMIE experimental setup. This study is focused on the evolution of nucleobases (uracil, cytosine…) in the presence of a calcium per-chlorate in the solid phase. Our results show that perchlorates accelerate the deg-radation of uracil under UV-irradiation compared to the evolution of uracil alone under the same UV flux. Concerning Cytosine, a new compound is formed during the sample preparation process (when this molecule is in contact with perchlorates before UV radiation exposure). The presence of UV radiation increases the photodegradation rate of this new compounds. From these results, it can be concluded that the presence of nucleobases and their photoproducts in the first centimeter depth of the martian regolith is highly uncertain

Testing the capabilities of the Mars Organic Molecule Analyser (MOMA) chromatographic columns for the separation of organic compounds on Mars

International audienceMars is our planetary neighbor and is now known to host trace levels of organic matter at its surface. However, little is known of the organic molecular composition or the survival potential for organic biosignatures, such as the enantiomeric excess of amino acids or the carbon chain patterns of lipid hydrocarbons, as a function of depth below the martian surface. The Mars Organic Molecule Analyser (MOMA) is an instrument onboard the Rosalind Franklin rover that is scheduled to be launched to Mars in the summer of 2020 as part of the ExoMars mission. This experiment includes a gas chromatograph instrument dedicated to the in situ analysis of organic molecules and their enantiomers present in martian samples collected by the rover at the surface down to 2 m depth. In order to evaluate the performance of the integrated chromatographic system which was selected for the flight model, experiments were carried out with a laboratory setup that reproduced the flight configuration and mimicked the in situ operating conditions. We show that the column instrument package can separate and detect a wide range of organic and inorganic volatile compounds, from noble gases to hydrocarbon chains with up to 29 carbon atoms (C29). We study the enantiomeric resolution of selected chiral chemical standards and compare our laboratory results to: i. tests performed with the same instrumental setup but using a natural sample spiked with amino acids in order to evaluate the influence of a mineral phase on the analysis, and ii. tests run on a MOMA engineering test unit (ETU) which is representative of the flight model. In each case, tests on the more complex sample and the more flight-like instrument allows a comparison with laboratory results, in order to confirm that laboratory data are reliable for supporting peak identification within flight data. The obtained results demonstrate the ability of the gas chromatographic subsystem to identify a wide range of organic and inorganic volatile compounds, including biomolecular signatures, within the constrained space operating conditions of MOMA. The results form a retention time and mass spectral database for MOMA which will be critical for analysis of the eventual flight data

Impact of nontronite on the evolution of organic molecules at the surface of Mars

International audienceSeveral evidences suggest that early Mars offered favorable conditions for long-term sustaining water. As a consequence, we can assume that in those days, endogenous chemical processes, or even primitive life, may have produced organic matter on Mars. Moreover, exogenous delivery from small bodies or dust particles is likely to brought fresh organic molecules to the surface of Mars until now. Organic matter is therefore expected to be present at the surface/subsurface of the planet. The search for these organic relics is one of the main objectives of Mars exploration missions. But current environmental conditions at the surface - UV radiation, oxidants and energetic particles - can generate physico-chemical processes that may affect organic molecules.Here we present results of laboratory investigations dedicated to monitor qualitative and quantitative evolutions of several organic molecules under simulated Martian surface ultraviolet light, mean temperature and pressure, using the Mars Organic Molecules Irradiation and Evolution setup. For each organic molecule, the nature of the evolution products (solid or gaseous) and the kinetic parameters (extrapolated half-life at Mars, quantum yields) were determined experimentally. The results show that when exposed to UV radiation, specific organic molecules lead to the formation of solid residues, probably of macromolecular nature, which could reach long term stability.On the other hand, we emphasize the study of the evolution of molecules in presence of nontronite, a clay mineral detected at the surface of Mars, highlights a strong protective effect of the clay reducing dissociation rates for some molecules, whereas a possible catalytic effect is tentatively observed for one studied molecule.These results are essential to support the analyses performed in situ by the past, current and future exploration missions. Moreover, the experimentally determined kinetic parameters provide new inputs for numerical modeling of Mars' current reservoir of organic molecules