The Petrochemistry of Jake_M: A Martian Mugearite

“Jake_M,” the first rock analyzed by the Alpha Particle X-ray Spectrometer instrument on the Curiosity rover, differs substantially in chemical composition from other known martian igneous rocks: It is alkaline (&gt;15% normative nepheline) and relatively fractionated. Jake_M is compositionally similar to terrestrial mugearites, a rock type typically found at ocean islands and continental rifts. By analogy with these comparable terrestrial rocks, Jake_M could have been produced by extensive fractional crystallization of a primary alkaline or transitional magma at elevated pressure, with or without elevated water contents. The discovery of Jake_M suggests that alkaline magmas may be more abundant on Mars than on Earth and that Curiosity could encounter even more fractionated alkaline rocks (for example, phonolites and trachytes).</jats:p

Mars’ Surface Radiation Environment Measured with the Mars Science Laboratory’s Curiosity Rover

The Radiation Assessment Detector (RAD) on the Mars Science Laboratory’s Curiosity rover began making detailed measurements of the cosmic ray and energetic particle radiation environment on the surface of Mars on 7 August 2012. We report and discuss measurements of the absorbed dose and dose equivalent from galactic cosmic rays and solar energetic particles on the martian surface for ~300 days of observations during the current solar maximum. These measurements provide insight into the radiation hazards associated with a human mission to the surface of Mars and provide an anchor point with which to model the subsurface radiation environment, with implications for microbial survival times of any possible extant or past life, as well as for the preservation of potential organic biosignatures of the ancient martian environment.</jats:p

Nucléation et croissance cristalline dans les silicates liquides

Les mécanismes microscopiques contrôlant la nucléation et la croissance cristalline à des températures inférieures au solidus, mais au-dessus de Tg ont été étudiés sur des verres du système CaO-AlzO3- SiOz. Les charges expérimentales ont été caractérisées à différentes échelles (MEB, MEr, microsonde, DRX, spectroscopie Raman). Les minéraux sont enrichis en Ca et possèdent un Al/Si proche de celui i du liquide parent. Un changement, progressif de ce rapport est observé avec la température. Ces résultats sont expliqués par les mobilités relatives des différents cations, celle de Ca étant supérieure de plusieurs ordres de grandeurs à celles de Si et Al. Le lien entre vitesse de croissance et viscosité a été testé et expliqué par l'origine microscopique commune des deux processus.: la rupture et les échanges de liaisons Si-O. Ce lien est rompu lorsque Si/Al du cristal et du liquide sont différents, la diffusion couplée de Al et Cà devenant le facteur limitant de la croissance minérale.Microscopic mechanisms controling crystal nucieation and growth at temperatures below the solidus 1 but above Tg have been studied on glasses in the system CaO-AlzO3-SiOz. Experimental charges have been characterized over a wide range of length scaIes (SEM, TEM, Microprobe, DRX, raman spectroscopy). Minerais are enriched in Ca and have Si/Al approaching that of the parent liquid. A gradual change of Al/Si is observed with temperature. These results are explained by the relative mobilities of the different cations, of which Ca is several orders of magnitude faster than that of Si and Al.. The link between crystal growth and viscosity has been tested and explained by the common microscopic origine of these processes which is the breaking and formation of Si-O bonds. This link is broken when Al/Si of crystals and liquids are different, because the coupled diffusion of Al and Ca becomes the limiting factor of the crystal growth.NANCY/VANDOEUVRE-INPL (545472102) / SudocSudocFranceF

Incorporation des gaz rares dans la matière organique primitive du système solaire

L'origine de la matière organique insoluble des météorites et des gaz rares associés est très mal comprise. Des expériences ont été effectuées lors de cette thèse afin de mieux cerner les environnements plausibles de formation. L'adsorption physique basse pression permet de reproduire les abondances et le fractionnement élémentaire des gaz rares pour un intervalle de température de 80- 100 K mais ne permet pas de rendre compte de la forte rétention des gaz rares dans la matière organique. De plus, les phénomènes d'adsoprtion n'induisent pas un fractionnement isotopique mesurable. Une expérience de solvatation sur la matière organique insoluble d'Orgueil (CI) révèle le piégeage dans le volume des gaz rares Pl. Ces résultats suggèrent un piégeage d'origine mécanique de ces gaz dans la structure organique. Deux mécanismes ont ainsi été testés pour reproduire ces caractéristiques. La sublimation-condensation de matière organique sous atmosphère de xénon ionisé permet de rendre compte du fractionnement isotopique de 1 %/uma observé pour les gaz rares Pl par rapport à la composante solaire. Ces résultats démontrent la possibilité de produire les caratéristiques du pôle Pl à partir d'une nébuleuse de compositon solaire. Cependant, ce mécanisme ne permet pas de reproduire les di-radicaux observés dans la matière organique insoluble des météorites par résonance paramagnétique électronique. Ce résultat tend à favoriser une origine interstellaire de la matière organique des météorites. A ce titre, un autre mécanisme a été étudié: le changement de phase nanodiamants oignons de carbone. Les nanodiamants représentent une importante quantité du carbone interstellaire et peuvent subir une transformation en oignons de carbone sous des conditions thermiques ou d'irradiations intenses. Des expériences de chauffage de nanodiamants sous une atmosphère de xénon ont été réalisées. Elles révélent la très grande rétention thermique du xénon piégé dans la nouvelle structure avec une température maximum de relâche située à 800ʿC. Outre leur très grande stabilité thermique, les oignons de carbone ont été observés dans les météorites et leur lien génétique avec les nanodiamants en font un des candidats les plus sérieux au titre de porteur des gaz rares Pl.The origin of the meteoritic organic matter and associated noble gases is poorly constrained. Experiments have been performed during this thesis in order to better constrain the possible environments of formation. Low pressure adsorption reproduces the concentration and elemental pattern of noble gases in the temperature range 80-100 K, but cannot explain the significant retention of noble gases within the organic structure. ln addition, Rayleigh-type distillation experiments induced by adsorption do not show measurable isotopic fractionation. A solvation experiment carried out on insoluble organic matter of Orgueil (CI) reveals the volume trapping of Pl noble gases. This result suggests a mechanical trapping of Pl noble gases in the organic structure. Two syntheses have been carried out in order to reproduce these characteristics. Sublimation- condensation experiments under an ionizing xenon atmosphere reproduces the isotopic fractionation observed for Pl noble gases compared to the solar composition. This result shows that the Pl composition can be generated from a nebula of solar composition. However, this condensation process does not allow the diradicaloids observed by electron paramagnetic resonance to be reproduced. This result strongly suggests an interstellar origin of insoluble organic matter and associated Pl noble gases. Then, the second mechanism was tested : the transformation of nanodiamonds to carbon onions. Nanodiamonds represent an important part of the interstellar carbon and could undergo change to carbon onions under heating or irradiation conditions. Nanodiamonds heating experiments have been carried out. They reveal significant retention of trapped xenon with the maximum temperature release occurring at 800ʿC. This characteristic, coupled with the detection of carbon onions in primitive meteorites and their genetic link with nanodiamonds, strongly suggests that this structure could be advocated as the Pl noble gas carrier in meteorites.NANCY/VANDOEUVRE-INPL (545472102) / SudocSudocFranceF

Regolith weathering through heating samples under reducing conditions for Phobos surface studies

International audienceAtmosphereless bodies of the Solar System present surface evolution under the harsh conditions of space weathering. Their regolith are exposed to thermal cycling, cosmic and solar rays irradiation, solar wind sputtering and micrometeorites bombardment and vaporization. With time these materials accumulate optically active opaque particles such as nanophase metallic iron particles on the surface or rims of dust grainsor larger iron particles. The density increase in iron particles modifies the spectral properties of the material with a lowering of the particlesalbedo, and of the absorption bands amplitude generally associated with a global reddening of the spectral slope [1, 2].Previous studies have shown that nanophase iron particles inducing weathering spectral properties will accumulate at the surface of olivine and pyroxene minerals under heating conditions simulating micrometeorite impacts [3]. The skin depth of weathered material depends on theweathering process and minerals.Laboratory simulations by heating samples under reducing conditions can recreate the conditions under which regolith may be weathered inspace with surface alteration of grains and apparition of nanophase iron on the altered depth. The effect of the changes on the grain spectralproperties depending on the experimental conditions will be further studied for applications to airless bodies in the Solar System. The sampleswill be analyzed with SEM at IRAP and their reflectance spectra acquired with the SHADOWS instrument at IPAG [12] for future comparisonswith the spectra of Phobos and Deimos

Regolith weathering through heating samples under reducing conditions for Phobos surface studies

International audienceAtmosphereless bodies of the Solar System present surface evolution under the harsh conditions of space weathering. Their regolith are exposed to thermal cycling, cosmic and solar rays irradiation, solar wind sputtering and micrometeorites bombardment and vaporization. With time these materials accumulate optically active opaque particles such as nanophase metallic iron particles on the surface or rims of dust grainsor larger iron particles. The density increase in iron particles modifies the spectral properties of the material with a lowering of the particlesalbedo, and of the absorption bands amplitude generally associated with a global reddening of the spectral slope [1, 2].Previous studies have shown that nanophase iron particles inducing weathering spectral properties will accumulate at the surface of olivine and pyroxene minerals under heating conditions simulating micrometeorite impacts [3]. The skin depth of weathered material depends on theweathering process and minerals.Laboratory simulations by heating samples under reducing conditions can recreate the conditions under which regolith may be weathered inspace with surface alteration of grains and apparition of nanophase iron on the altered depth. The effect of the changes on the grain spectralproperties depending on the experimental conditions will be further studied for applications to airless bodies in the Solar System. The sampleswill be analyzed with SEM at IRAP and their reflectance spectra acquired with the SHADOWS instrument at IPAG [12] for future comparisonswith the spectra of Phobos and Deimos

Regolith weathering through heating samples under reducing conditions for Phobos surface studies

International audienceAtmosphereless bodies of the Solar System present surface evolution under the harsh conditions of space weathering. Their regolith are exposed to thermal cycling, cosmic and solar rays irradiation, solar wind sputtering and micrometeorites bombardment and vaporization. With time these materials accumulate optically active opaque particles such as nanophase metallic iron particles on the surface or rims of dust grainsor larger iron particles. The density increase in iron particles modifies the spectral properties of the material with a lowering of the particlesalbedo, and of the absorption bands amplitude generally associated with a global reddening of the spectral slope [1, 2].Previous studies have shown that nanophase iron particles inducing weathering spectral properties will accumulate at the surface of olivine and pyroxene minerals under heating conditions simulating micrometeorite impacts [3]. The skin depth of weathered material depends on theweathering process and minerals.Laboratory simulations by heating samples under reducing conditions can recreate the conditions under which regolith may be weathered inspace with surface alteration of grains and apparition of nanophase iron on the altered depth. The effect of the changes on the grain spectralproperties depending on the experimental conditions will be further studied for applications to airless bodies in the Solar System. The sampleswill be analyzed with SEM at IRAP and their reflectance spectra acquired with the SHADOWS instrument at IPAG [12] for future comparisonswith the spectra of Phobos and Deimos

Détermination de la solubilité de Cr2O3 dans les verres: relation avec la résistance à la corrosion des super-alliages chromine-formeurs par les verres fondus

Augmentation de la solubilité :* avec la température et la teneur en oxydes alcalins* avec la pression partielle en oxygène pour les verres binairesAugmentation de la teneur en CrVI et diminution de la teneur en CrIII :* avec la teneur en Na2O* avec la pression partielle en O2Les enthalpies de solubilité :* sont positives ( processus de dissolution endothermique)* augmentent avec la teneur en oxydes alcalin