The 15N-enrichment in dark clouds and Solar System objects

The line intensities of the fundamental rotational transitions of H13CN and HC15N were observed towards two prestellar cores, L183 and L1544, and lead to molecular isotopic ratios 140 6 14N/15N 6 250 and 140 6 14N/15N 6 360, respectively. The range of values reflect genuine spatial variations within the cores. A comprehensive analysis of the available measurements of the nitrogen isotopic ratio in prestellar cores show that molecules carrying the nitrile functional group appear to be systematically 15N-enriched com- pared to those carrying the amine functional group. A chemical origin for the differential 15N-enhance- ment between nitrile- and amine-bearing interstellar molecules is proposed. This sheds new light on several observations of Solar System objects: (i) the similar N isotopic fractionation in Jupiter's NH3 and solar wind N+; (ii) the 15N-enrichments in cometary HCN and CN (that might represent a direct inter- stellar inheritance); and (iii) 15N-enrichments observed in organics in primitive cosmomaterials. The large variations in the isotopic composition of N-bearing molecules in Solar System objects might then simply reflect the different interstellar N reservoirs from which they are originating

The Surface Compositions of Triton, Pluto, and Charon

Neptune's satellite Triton, and the planet-satellite binary Pluto and Charon, are the most distant planetary bodies on which ices have been directly detected. Triton and Pluto have very similar dimensions and mean densities, suggesting a similar or common origin. Through earth-based spectroscopic observations in the near-infrared, solid N2, CH4, and CO have been found on both bodies, with the additional molecule C02 on Triton. N2 dominates both surfaces, although the coverage is not spatially uniform. On Triton, the CH4 and CO are mostly or entirely frozen in the N2 matrix, while CO2 may be spatially segregated. On Pluto, some CH4 and the CO are frozen in the N2 matrix, but there is evidence for additional CH4 in a pure state, perhaps lying as a lag deposit on a subsurface layer of N2. Despite their compositional and dimensional similarities, Pluto and Triton are quite different from one another in detail. Additional hydrocarbons and other volatile ices have been sought spectroscopically but not yet have been detected. The only molecule identified on Pluto's satellite Charon is solid H2O, but the spectroscopic data are of low precision and admit the presence of other ices such as CH4

Identification of Ammonium Salts on Comet 67P/C-G Surface from Infrared VIRTIS/Rosetta Data Based on Laboratory Experiments. Implications and Perspectives

The nucleus of comet 67P/Churyumov-Gerasimenko exhibits a broad spectral reflectance feature around 3.2 $\mu$m, which is omnipresent in all spectra of the surface, and whose attribution has remained elusive since its discovery. Based on laboratory experiments, we have shown that most of this absorption feature is due to ammonium (NH4+) salts mixed with the dark surface material. The depth of the band is compatible with semi-volatile ammonium salts being a major reservoir of nitrogen in the comet, which could dominate over refractory organic matter and volatile species. These salts may thus represent the long-sought reservoir of nitrogen in comets, possibly bringing their nitrogen-to-carbon ratio in agreement with the solar value. Moreover, the reflectance spectra of several asteroids are compatible with the presence of NH4+ salts at their surfaces. The presence of such salts, and other NH4+-bearing compounds on asteroids, comets, and possibly in proto-stellar environments, suggests that NH4+ may be a tracer of the incorporation and transformation of nitrogen in ices, minerals and organics, at different phases of the formation of the Solar System

Photometric correction for VIRTIS-M data of comet 67P/CG

VIRTIS, the Visible Infrared Thermal Imaging Spectrometer onboard the Rosetta orbiter [1], has acquired so far millions of spectra of the comet 67P/Churyumov-Gerasimenko [2]. The instrument is composed of two subsystems: a high-resolution channel (VIRTIS-H) which is a punctual spectrometer (2.0-5-0 µm) and the mapper (VIRTIS-M) able to produce hyper-spectral images of the target (0.25-5.1 µm). The huge amount of data produced by VIRTIS has been acquired under different observation and illumination conditions. This induces photometric effects on the measured signal that need to be quantified and removed, in order to characterize the intrinsic spectral variability of the surface. To achieve this task we computed a photometric correction from VIRTIS-M data (Ciarniello et al, 2015), starting from August 2014, when the nucleus was largely resolved (MTP006-MT007 observation sequences) by means of a simplified Hapke model [3]. The global surface single particle phase function (SPPF) and the single scattering albedo (SSA) are determined as well as the effect of sub-pixel roughness is discussed. Comparisons with photometric properties of other comets are shown. This work is supported by the Italian Space Agency (ASI. We acknowledge funding from French and German space agency. References 1- Coradini et al, SSR, 2007 2- Capaccioni et al., Science, in Press, 2015 3- Hapke, Theory of reflectance and emittance spectroscopy. Cambridge University Press, 2012 <P /

Structure of primitive polyaromatic carbonaceous matter : IDPs versus chondrites

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UV Raman Spectroscopy as a Powerful Tool for Investigating Insoluable Organic Matter of Chondrites and Cometary Dust

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Effects of Secondary Processes on the Isotopic Composition of Insoluble Organic Matter

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Metamorphic Control of Noble Gas Abundances in Pristine Chondrites

International audienceThe structure and texture of IOM was studied by HRTEM in Kaba, Leoville, Mokoia, Allende,Tieschitz. We revisit the question of the metamorphic control of the Q (P1), P3 and P6 components, the carrier of the Q phase