Characterising the CI and CI-like carbonaceous chondrites using thermogravimetric analysis and infrared spectroscopy

The CI and CI-like chondrites provide a record of aqueous alteration in the early solar system. However, the CI-like chondrites differ in having also experienced a late stage period of thermal metamorphism. In order to constrain the nature and extent of the aqueous and thermal alteration, we have investigated the bulk mineralogy and abundance of H2O in the CI and CI-like chondrites using thermogravimetric analysis and infrared spectroscopy. The CI chondrites Ivuna and Orgueil show significant mass loss (28.5–31.8 wt.%) upon heating to 1000 °C due to dehydration and dehydroxylation of abundant phyllosilicates and Fe-(oxy)hydroxides and the decomposition of Fe-sulphides, carbonates and organics. Infrared spectra for Ivuna and Orgueil have a prominent 3-μm feature due to bound −OH/H2O in phyllosilicates and Fe-(oxy)hydroxides and only a minor 11-μm feature from anhydrous silicates. These characteristics are consistent with previous studies indicating that the CI chondrites underwent near-complete aqueous alteration. Similarities in the total abundance of H2O and 3 μm/11 μm ratio suggest that there is no difference in the relative degree of hydration experienced by Ivuna and Orgueil. In contrast, the CI-like chondrites Y-82162 and Y-980115 show lower mass loss (13.8–18.8 wt.%) and contain >50 % less H2O than the CI chondrites. The 3-μm feature is almost absent from spectra of Y-82162 and Y-980115 but the 11-μm feature is intense. The CI-like chondrites experienced thermal metamorphism at temperatures >500 °C that initially caused dehydration and dehydroxylation of phyllosilicates before partial recrystallization back into anhydrous silicates. The surfaces of many C-type asteroids were probably heated through impact metamorphism and/or solar radiation, so thermally altered carbonaceous chondrites are likely good analogues for samples that will be returned by the Hayabusa-2 and OSIRIS-REx missions

Orbitrap-MS and Chromatography in Preparation for Hayabusa2 Molecular Complexity Analyses

International audienceHigh resolution mass spectrometry is coupled with liquid chromatography to investigate the organic content of very small amount of extraterrestrial samples

Mid-infrared study of the molecular structure variability of insoluble organic matter from primitive chondrites

International audienceInsoluble Organic Matter (IOM) found in primitive meteorites was formed in the Early Solar System and subsequently processed on the parent asteroids. The location, temporal sequence and processes of formation of this IOM are still a matter of debate. In particular, there is no consensus on the actual effect of post-accretional aqueous alteration processes on the chemical composition and structure of IOM. In the most primitive chondrites (types 1 and 2), these alterations have so far been either neglected or generically assigned to oxidation processes induced by fluid circulation. A series of IOM samples extracted from 14 chondrites with extensively documented post-accretional histories have been studied by infrared spectroscopy. Aqueous alteration shows no detectable effect on the chemical composition and structure of IOM within or across chondrite classes. Indeed, the most effective post-accretional process appears to be a high-temperature short-duration heating event and concerns essentially type 2 chondrites. In any case, post-accretional processes cannot account for all the chemical and structural variations of IOM. Chondrites from the CI, CR and CM classes accreted IOM precursors with moderately variable compositions, suggesting a chemical heterogeneity of the protosolar disk. The 3.4 μm band, and possibly its overtones and combinations in the near-infrared range, appear to be tracer(s) of the chemical class and possibly of surface heating processes triggered by impacts

Micrometeorites soluble organic mixture analysed by Nanospray Ion Source Orbitrap mass spectrometry

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Presolar SiC abundances in primitive meteorites by NanoSIMS raster ion imaging of insoluble organic matter

Here we present results obtained with NanoSIMS raster ion imaging to determine the abundance of presolar SiC in the insoluble organic matter (IOM) extracted from a number of different classes of chondrites (both carbonaceous and ordinary). This builds on previous work [1] aimed at obtaining SiC abundances in primitive meteorites by SIMS and comparing them with noble gas analyses. Both IOM and presolar grains are found in similar CI-like relative abundances in the matrices of the most primitive chondrites [2, 3], indicating that a homogeneous mixture of grains was incorporated in the various parent bodies [3]. Both are then subjected to thermal and hydrothermal processing after parent body formation [4]. However, there are significant variations in the matrix-normalized abundances of SiC grains estimated from noble gases carried by presolar grains, which suggest that the primitive chondrites did not form from a well-mixed reservoir of presolar grains. Variations in the source material were attributed to the destruction of presolar grains by heating in the solar nebula (temperatures that may have exceeded 700°C) and were linked to the volatile element fractionations in chondrites [5]. The CR chondrites have amongst the lowest matrix-normalized SiC abundances, and largest volatile element ractionations, reported in the carbonaceous chondrites [5]. However, they contain the most primitive IOM of any chondrite class [6-7], which has experienced peak temperatures of <300°C [8]. These lowtemperatures could not have affected the SiC grains or their noble gas concentrations, indicating that either the IOM escaped heating (implying that it is not presolar)or SiC was degassed/destroyed at low temperatures, perhaps during parent body processing [3]. Thus, in order to resolve this contradiction, it is necessary to determine SiC abundances independently of noble gases. Ion imaging of SiC grains is a direct technique that has been shown to successfully identify presolar SiC grains amongst others

Micrometeorites soluble organic mixture analysed by Nanospray Ion Source Orbitrap mass spectrometry

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Micrometeorites soluble organic mixture analysed by Nanospray Ion Source Orbitrap mass spectrometry

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The Multiple Origins of Insoluble Organic Matter from Primitive Chondrites

We present a study by IR and Raman of the insoluble organic matter from 28 CI, CR, CM and ung-C2 chondrites. We evidence a chemical heterogeneity of the solar nebula and that thermal heating was the sole parent body process that modified IOM

Laboratory Simulation of Pluto's Atmosphere and Aerosols

International audienceWe will present laboratory investigation of Pluto's atmosphere and its aerosols formation to help understand the data provided by the New Horizons spacecraft