Recherche d'indices de vie sur Mars : Caractérisation de l'évolution de molécules organiques soumises aux conditions d'irradiation et d'oxydation représentatives de la surface de Mars

The search for mineral or organic clues of past or present habitability at the surface of Mars is one of the main objectives of the martian exploration program. Numerous organic molecules could have been brought or synthesized at the Mars surface until its formation, but no evidence of their presence on Mars was found up today. However the current martian environmental conditions are favorable to the evolution or even the degradation of organic matter because of the presence of energetic ultraviolet radiations, energetic particles and oxidation processes. The understanding of how organic molecules can evolve in this environment would allow to prepare and help for the interpretation of the data collected by the future martian in situ exploration missions as MSL 2011 and ExoMars 2018. To characterize the organic matter evolution at the surface of Mars I developed an original experimental device allowing to follow the evolution of organic molecules exposed to irradiation and oxidation processes occurring at the Mars surface. This experimental device is able to simulate the interactions between organic matter, mineral phases, water ice and UV radiation. The first target of this study is glycine, a biologic amino acid. The glycine is rapidly photodissociated under the temperature and pressure conditions representative of the martian environment. The mineral particles did not catalyze or protect the glycine, contrary to the water ice accelerating the glycine degradation probably through the formation of radical species during the water ice photolysis. These experiments allowed the qualification of the device and offer many opportunities.La recherche de traces minérales ou organiques témoignant d'une habitabilité passée ou présente de la surface de la planète Mars est au coeur du programme d'exploration de la planète. De nombreuses molécules organiques ont pu être apportées ou synthétisées à la surface depuis la formation de la planète. Cependant, aucune molécule organique n'a été identifiée de manière ferme jusqu'à aujourd'hui. Or, les conditions environnementales martiennes actuelles sont favorables à l'évolution voire à la dégradation des molécules organiques à cause de la présence de rayonnement ultraviolet énergétique, de particules énergétiques et de processus d'oxydation. La compréhension de l'évolution des molécules organiques dans cet environnement permettra de préparer et d'aider à l'interprétation de futures missions d'exploration in situ de la surface de Mars comme les missions MSL 2011 et ExoMars 2018. Afin de caractériser l'évolution de la matière organique à la surface de Mars, j'ai développé un dispositif expérimental original permettant d'étudier l'évolution de molécules organiques soumises aux conditions d'irradiation et d'oxydation régnant à la surface de Mars. Ce dispositif est capable de simuler les interactions entre la matière organique, les phases minérales, la glace d'eau et le rayonnement UV. La première cible de cette étude est la glycine, un acide aminé du vivant. La glycine est rapidement photodissociée dans les conditions de température et de pression représentatives de la surface de Mars. La présence de particules minérales ne provoque pas d'effet catalyseur ou de protecteur sur l'évolution de la glycine. Au contraire la présence de glace d'eau semble accélérer la dégradation de la glycine, probablement grâce à la formation d'espèces radicalaires lors de la photolyse de la glace d'eau. Ces expériences ont permis de qualifier le dispositif expérimental et ouvrir de nombreuses perspectives

Recherche d'indices de vie sur Mars : Caractérisation de l'évolution de molécules organiques soumises aux conditions d'irradiation et d'oxydation représentatives de la surface de Mars

The search for mineral or organic clues of past or present habitability at the surface of Mars is one of the main objectives of the martian exploration program. Numerous organic molecules could have been brought or synthesized at the Mars surface until its formation, but no evidence of their presence on Mars was found up today. However the current martian environmental conditions are favorable to the evolution or even the degradation of organic matter because of the presence of energetic ultraviolet radiations, energetic particles and oxidation processes. The understanding of how organic molecules can evolve in this environment would allow to prepare and help for the interpretation of the data collected by the future martian in situ exploration missions as MSL 2011 and ExoMars 2018. To characterize the organic matter evolution at the surface of Mars I developed an original experimental device allowing to follow the evolution of organic molecules exposed to irradiation and oxidation processes occurring at the Mars surface. This experimental device is able to simulate the interactions between organic matter, mineral phases, water ice and UV radiation. The first target of this study is glycine, a biologic amino acid. The glycine is rapidly photodissociated under the temperature and pressure conditions representative of the martian environment. The mineral particles did not catalyze or protect the glycine, contrary to the water ice accelerating the glycine degradation probably through the formation of radical species during the water ice photolysis. These experiments allowed the qualification of the device and offer many opportunities.La recherche de traces minérales ou organiques témoignant d'une habitabilité passée ou présente de la surface de la planète Mars est au coeur du programme d'exploration de la planète. De nombreuses molécules organiques ont pu être apportées ou synthétisées à la surface depuis la formation de la planète. Cependant, aucune molécule organique n'a été identifiée de manière ferme jusqu'à aujourd'hui. Or, les conditions environnementales martiennes actuelles sont favorables à l'évolution voire à la dégradation des molécules organiques à cause de la présence de rayonnement ultraviolet énergétique, de particules énergétiques et de processus d'oxydation. La compréhension de l'évolution des molécules organiques dans cet environnement permettra de préparer et d'aider à l'interprétation de futures missions d'exploration in situ de la surface de Mars comme les missions MSL 2011 et ExoMars 2018. Afin de caractériser l'évolution de la matière organique à la surface de Mars, j'ai développé un dispositif expérimental original permettant d'étudier l'évolution de molécules organiques soumises aux conditions d'irradiation et d'oxydation régnant à la surface de Mars. Ce dispositif est capable de simuler les interactions entre la matière organique, les phases minérales, la glace d'eau et le rayonnement UV. La première cible de cette étude est la glycine, un acide aminé du vivant. La glycine est rapidement photodissociée dans les conditions de température et de pression représentatives de la surface de Mars. La présence de particules minérales ne provoque pas d'effet catalyseur ou de protecteur sur l'évolution de la glycine. Au contraire la présence de glace d'eau semble accélérer la dégradation de la glycine, probablement grâce à la formation d'espèces radicalaires lors de la photolyse de la glace d'eau. Ces expériences ont permis de qualifier le dispositif expérimental et ouvrir de nombreuses perspectives

Recherche d'indices de vie sur Mars (caractérisation de l'évolution de molécules organiques soumises aux conditions d'irradiation et d'oxydation représentatives de la surface de Mars)

PARIS7-Bibliothèque centrale (751132105) / SudocSudocFranceF

Quantum efficiency of excitonic enhancement in nanosensors by rainbow nonlinear optical spectroscopy

editorial reviewedQuantum dots (QD) constitute a novel generation of fluorescent probes due to their confined size in the 1-10 nm range. In this field, nanosensors sensitivity is of pivotal importance to target biomolecules. We focus here on the grafting of organic ligand-coated CdTe QDs monolayers on glass surfaces to address the environmental problem and cost of nanosensors. QD monolayers samples are pre-characterized by UV-VIS absorption and (Time-resolved) fluorescence emission, evidencing the success of transferring the QD optoelectronic properties from colloidal solution to amine-terminated aliphatic organosilane monolayer-modified glass samples. Moreover, from time-resolved fluorescence spectroscopy, the effect of chemical structure of monolayers are seen from a fast-quenching phenomenon in relation to colloidal QD solution. Afterwards, an advanced surface-specific spectroscopic tool, non-linear optical Two-Colour IR-Visible Sum-Frequency Generation spectroscopy (2C-SFG), is used to probe and evidences the dipolar coupling between QD excitons and their molecular surroundings, which improves the nanosensor’s detection threshold. This electro-optical coupling (inorganic-organic charge transfer) is modelled in an original formalism we developed and based on Feynman loop-diagrams

UVolution, a photochemistry experiment in low earth orbit: Investigation of the photostability of carbonates exposed to martian-like UV radiation conditions

International audienceThe detection and identification of carbonates on Mars are of prime importance to establish the evolution of its atmosphere, correlated to the history of the liquid water, or even to determine the existence of a possible ancient biological activity. To date, no large deposits of carbonates have been found. In fact, their detection is specific to local areas and in very low amounts. The absence of such deposits is commonly attributed to the harsh environmental conditions at the surface of Mars. Additionally, the presence of UV radiation has been proposed to explain their photodecomposition and hence their absence. However, contradictory results from laboratory experiments mimicking Mars' surface UV radiation did not resolve the behaviour of carbonates in such an environment, which is why we exposed, in low Earth orbit and in laboratory experiments, both abiotic and biotic calcium carbonates to UV radiation of wavelength above 200 nm, the same spectral distribution as the one reaching the surface of Mars. For low Earth orbit (LEO) exposure, this was done for the UVolution experiment on board the BIOPAN ESA module, which was set outside a Russian Foton automated capsule, and exposed to space conditions for 12 days in September 2007. The targeted carbonates are biominerals and abiotic samples. Our laboratory results mainly show that the exposed carbonates appear to be stable to UV radiation if directly exposed to it. The LEO experiment results tend to the same conclusion, but the integrated exposition time to Solar UV during the experiment is not sufficient to be conclusive. However, the stability of the biominerals derived from the laboratory experiment could strengthen the interest to explore deeper their potential as life records at Mars. Hence, they should be considered as primary targets for in situ analyses during future missions

Oxidants at the Surface of Mars: A Review in Light of Recent Exploration Results

International audienceIn 1976, the Viking landers carried out the most comprehensive search for organics and microbial life in the martian regolith. Their results indicate that Mars' surface is lifeless and, surprisingly, depleted in organics at part-per-billion levels. Several biology experiments on the Viking landers gave controversial results that have since been explained by the presence of oxidizing agents on the surface of Mars. These oxidants may degrade abiotic or biological organics, resulting in their nondetection in the regolith. As several exploration missions currently focus on the detection of organics on Mars (or will do so in the near future), knowledge of the oxidative state of the surface is fundamental. It will allow for determination of the capability of organics to survive on a geological timescale, the most favorable places to seek them, and the best methods to process the samples collected at the surface. With this aim, we review the main oxidants assumed to be present on Mars, their possible formation pathways, and those laboratory studies in which their reactivity with organics under Mars-like conditions has been evaluated. Among the oxidants assumed to be present on Mars, only four have been detected so far: perchlorate ions (ClO4-) in salts, hydrogen peroxide (H2O2) in the atmosphere, and clays and metal oxides composing surface minerals. Clays have been suggested as catalysts for the oxidation of organics but are treated as oxidants in the following to keep the structure of this article straightforward. This work provides an insight into the oxidizing potential of the surface of Mars and an estimate of the stability of organic matter in an oxidizing environment

The PROCESS Experiment: Amino and Carboxylic Acids Under Mars-Like Surface UV Radiation Conditions in Low-Earth Orbit

International audienceThe search for organic molecules at the surface of Mars is a top priority of the next Mars exploration space missions: Mars Science Laboratory (NASA) and ExoMars (ESA). The detection of organic matter could provide information about the presence of a prebiotic chemistry or even biological activity on this planet. Therefore, a key step in interpretation of future data collected by these missions is to understand the preservation of organic matter in the martian environment. Several laboratory experiments have been devoted to quantifying and qualifying the evolution of organic molecules under simulated environmental conditions of Mars. However, these laboratory simulations are limited, and one major constraint is the reproduction of the UV spectrum that reaches the surface of Mars. As part of the PROCESS experiment of the European EXPOSE-E mission on board the International Space Station, a study was performed on the photodegradation of organics under filtered extraterrestrial solar electromagnetic radiation that mimics Mars-like surface UV radiation conditions. Glycine, serine, phthalic acid, phthalic acid in the presence of a mineral phase, and mellitic acid were exposed to these conditions for 1.5 years, and their evolution was determined by Fourier transform infrared spectroscopy after their retrieval. The results were compared with data from laboratory experiments. A 1.5-year exposure to Mars-like surface UV radiation conditions in space resulted in complete degradation of the organic compounds. Half-lives between 50 and 150 h for martian surface conditions were calculated from both laboratory and low-Earth orbit experiments. The results highlight that none of those organics are stable under low-Earth orbit solar UV radiation conditions

The PROCESS Experiment: An Astrochemistry Laboratory for Solid and Gaseous Organic Samples in Low-Earth Orbit

International audienceThe PROCESS (PRebiotic Organic ChEmistry on the Space Station) experiment was part of the EXPOSE-E payload outside the European Columbus module of the International Space Station from February 2008 to August 2009. During this interval, organic samples were exposed to space conditions to simulate their evolution in various astrophysical environments. The samples used represent organic species related to the evolution of organic matter on the small bodies of the Solar System (carbonaceous asteroids and comets), the photolysis of methane in the atmosphere of Titan, and the search for organic matter at the surface of Mars. This paper describes the hardware developed for this experiment as well as the results for the glycine solid-phase samples and the gas-phase samples that were used with regard to the atmosphere of Titan. Lessons learned from this experiment are also presented for future low-Earth orbit astrochemistry investigations