Organics Captured from Comet Wild 2 by the Stardust Spacecraft

Organics found in Comet Wild 2 samples show a heterogeneous and unequilibrated distribution in abundance and composition. Some are similar, but not identical, to those in interplanetary dust particles (IDPs) and carbonaceous meteorites. A new class of aromatic-poor organic material is also present. The organics are rich in O and N compared to meteoritic organics. Aromatic compounds are present, but the samples tend to be relatively poorer in aromatics than meteorites and IDPs. D and 15N suggest that some organics have an interstellar/protostellar heritage. While the variable extent of modification of these materials by impact capture is not yet fully constrained, a remarkably diverse suite of organic compounds is present and identifiable within the returned samples

LES SILICATES INTERSTELLAIRES (COMPOSITION PHYSICO-CHIMIQUE ET EVOLUTION)

ORSAY-PARIS 11-BU Sciences (914712101) / SudocMEUDON-Observatoire (920482302) / SudocSudocFranceF

The amino acid and hydrocarbon contents of the Paris meteorite, the most primitive CM chondrite

International audienceThe Paris meteorite is reported to be the least aqueously altered CM chondrite [1,2], and to have experienced only weak thermal metamorphism [2-5]. The IR spectra of some of Paris' fragments suggest a primitive origin for the organic matter in this meteorite, similar to the spectra from solid-state materials in molecular clouds [6]. Most of the micron-sized organic particles present in the Paris matrix exhibit 0 < delta

The amino acid and hydrocarbon contents of the Paris meteorite, the most primitive CM chondrite

International audienceThe Paris meteorite is reported to be the least aqueously altered CM chondrite [1,2], and to have experienced only weak thermal metamorphism [2-5]. The IR spectra of some of Paris' fragments suggest a primitive origin for the organic matter in this meteorite, similar to the spectra from solid-state materials in molecular clouds [6]. Most of the micron-sized organic particles present in the Paris matrix exhibit 0 < delta

La chimie des glaces interstellaires: à la recherche des molecules du vivant? Interstellar ices chemistry: the search for the molecules of life?

International audienceOrganic molecules observed in the interstellar medium (ISM) are provided by a chemistry, which takes place in extreme conditions (temperature of 10-20 K, very low pressures, very intense and energetic radiative fluxes). These molecules can be formed in solid phase on water ice surfaces where the ice is taken as a catalyst. In this article, we are interested in the composition and formation of the interstellar ices which are known from astrophysical observations, essentially from infrared spectroscopy. We show how these ices can be simulated in the laboratory and how they can evolve through photochemical and thermal reactions. In the last part, we show that in the current state of research, some indications allow astrochemists to think that the precursor molecules of the amino-acids and pyrimidic bases can be formed in interstellar space, opening way to the prebiotic astrochemistry.Les nombreuses molécules organiques observées dans le milieu interstellaire (MIS) proviennent d'une chimie en conditions extrêmes, à savoir une très basse température de 10-20 K, une pression très faible et un environnement radiatif intense et très énergétique. Ces molécules peuvent se former en phase solide sur des surfaces de glaces principalement constituées d'eau qui jouent un rôle de catalyseur. Dans cet article, nous nous intéressons à la composition et à la formation des glaces interstellaires qui sont connues à partir de moyens d'observation astrophysiques, essentiellement grâce à la spectroscopie infrarouge. Nous montrons comment ces glaces sont reproduites en laboratoire et la manière dont les réactivités photochimiques et thermiques permettent de les faire évoluer vers la complexité moléculaire. Dans la dernière partie, nous montrons qu'en l'état actuel des recherches dans ce domaine, beaucoup d'éléments laissent penser que les molécules précurseurs des acides aminés et des bases pyrimidiques peuvent se former dans l'espace interstellaire, ouvrant alors la voie à l'astrochimie prébiotique. Mots-clés Astrophysique, astrochimie, photochimie, glace d'eau, chimie prébiotique, milieu interstellaire, spectroscopie infrarouge

A micro-Raman survey of 10 IDPs and 6 carbonaceous chondrites

International audienceThis paper presents a micro-Raman survey of a set of 10 IDPs and 6 pristine carbonaceous chondrites. The higher sensitivity of the present micro-spectrometers allowed to record a dozen of spectra for each objects, whereas only one was available in previous studies. First, as in previous studies, the first-order carbon bands G and D were the only detected features, superimposed onto a fluorescence background of variable intensity, and the spectral characteristics of these bands point to a very disordered polyaromatic organic matter (OM). Nevertheless, these new data reveal that in IDPs, unlike chondrites, the presence of the Raman bands is not systematic, evidencing a much higher heterogeneity in the spatial distribution or the chemical composition of OM. Second, as a consequence, a single spectrum is not representative of a whole IDP, and the classification previously proposed by Wopenka [ 1988. Raman observations on individual interplanetary dust particules. Earth and Planet. Sci. Lett. 88, 221—231.] is no longer tenable. At last, this study shows that the fluorescence signal induced by the laser irradiation mostly originates from OM

Methylammonium methylcarbamate thermal formation in interstellar ice analogs: a glycine salt precursor in protostellar environments

International audienceContext. Analyses of dust cometary grains collected by the Stardust spacecraft have shown the presence of amines and amino acids molecules, and among them glycine (NH 2 CH 2 COOH). We show how the glycine molecule could be produced in the protostellar environments before its introduction into comets. Aims. We study the evolution of the interstellar ice analogues affected by both thermal heating and vacuum ultraviolet (VUV) photons, in addition to the nature of the formed molecules and the confrontation of our experimental results with astronomical observations. Methods. Infrared spectroscopy and mass spectrometry are used to monitor the evolution of the H 2 O:CO 2 :CH 3 NH 2 and CO 2 :CH 3 NH 2 ice mixtures during both warming processes and VUV photolysis. Results. We first show how carbon dioxide (CO 2) and methylamine (CH 3 NH 2) thermally react in water-dominated ice to form methylammonium methylcarbamate [CH 3 NH + 3 ][CH 3 NHCOO − ] noted C. We then determine the reaction rate and activation energy. We show that C thermal formation can occurs in the 50-70 K temperature range of a protostellar environment. Secondly, we report that a VUV photolysis of a pure C sample produces a glycine salt, methylammonium glycinate [CH 3 NH + 3 ][NH 2 CH 2 COO − ] noted G. We propose a scenario explaining how C and subsequently G can be synthesized in interstellar ices and precometary grains. Conclusions. [CH 3 NH + 3 ][CH 3 NHCOO − ] could be readily formed and would act as a glycine salt precursor in protostellar environments dominated by thermal and UV processing. We propose a new pathway leading to a glycine salt, which is consistent with the detection of glycine and methylamine within the returned samples of comet 81P/Wild 2 from the Stardust mission