Yves Marrocchi^1,2, Matthieu Gounelle^3,4, Ingrid Blanchard^3,5, Florent Caste^3,6 and Anton T. Kearsley⁷

¹Université de Lorraine, CRPG, UMR 7358, Vandoeuvre les Nancy, France
²CNRS, CRPG UMR 7358, Vandoeuvre les Nancy, France
³Laboratoire de Minéralogie et de Cosmochimie du Muséum, MNHN and CNRS, UMR 7202, Paris, France
⁴Institut Universitaire de France, Maison des Universités, Paris, France
⁵Institut de Physique du Globe de Paris, Sorbonne Paris Cité, Université Paris Diderot, UMR 7154 CNRS, Paris, France
⁶Institut de Minéralogie et de Physique des Milieux Condensés, UMR 7590, CNRS-UPMC, Paris, France
⁷Imaging and Analysis Centre, Department of Science Facilities, Natural History Museum, London, UK

We report a petrographic and mineralogical survey of Paris, a new CM chondrite considered to be the least-altered CM identified so far (Hewins et al. 2014). Compared to other CMs, Paris exhibits (1) a higher concentration of Fe-Ni metal beads, with nickel contents in the range 4.1–8.1 wt%; (2) the systematic presence of thin lamellae and tiny blebs of pentlandite in pyrrhotite grains; and (3) ubiquitous tochilinite/cronstedtite associations with higher FeO/SiO₂ and S/SiO₂ ratios. In addition, Paris shows the highest concentration of trapped ³⁶Ar reported so far for a CM chondrite (Hewins et al. 2014). In combination with the findings of previous studies, our data confirm the reliability of (1) the alteration sequence based on the chemical composition of tochilinite/cronstedtite associations to quantify the fluid alteration processes and (2) the use of Cr content variability in type II ferroan chondrule olivine as a proxy of thermal metamorphism. In contrast, the scales based on (1) the Fe³⁺ content of serpentine in the matrix to estimate the degree of aqueous alteration and (2) the chemical composition of Fe-Ni metal beads for quantifying the intensity of the thermal metamorphism are not supported by the characteristics of Paris. It also appears that the amount of trapped ³⁶Ar is a sensitive indicator of the secondary alteration modifications experienced by chondrites, for both aqueous alteration and thermal metamorphism. Considering Paris, our data suggest that this chondrite should be classified as type 2.7 as it suffered limited but significant fluid alteration and only mild thermal metamorphism. These results point out that two separated scales should be used to quantify the degree of the respective role of aqueous alteration and thermal metamorphism in establishing the characteristics of CM chondrites.

Reference
Marrocchi Y, Gounelle M, Blanchard I, Caste F and Kearsley AT (in press) The Paris CM chondrite: Secondary minerals and asteroidal processing. Meteoritics & Planetary Science
[doi:10.1111/maps.12329]
Published by arrangement with John Wiley & Sons

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Sterken, V. J¹ et al. (>10)*
*Find the extensive, full author and affiliation list on the publishers website.

¹Institut für Raumfahrtsysteme, University Stuttgart, Stuttgart, Germany

On the basis of an interstellar dust model compatible with Ulysses and Galileo observations, we calculate and predict the trajectories of interstellar dust (ISD) in the solar system and the distribution of the impact speeds, directions, and flux of ISD particles on the Stardust Interstellar Dust Collector during the two collection periods of the mission. We find that the expected impact velocities are generally low (<10 km s⁻¹) for particles with the ratio of the solar radiation pressure force to the solar gravitational force β > 1, and that some of the particles will impact on the cometary side of the collector. If we assume astronomical silicates for particle material and a density of 2 g cm⁻³, and use the Ulysses measurements and the ISD trajectory simulations, we conclude that the total number of (detectable) captured ISD particles may be on the order of 50. In companion papers in this volume, we report the discovery of three interstellar dust candidates in the Stardust aerogel tiles. The impact directions and speeds of these candidates are consistent with those calculated from our ISD propagation model, within the uncertainties of the model and of the observations.

Reference
Sterken et al. (in press) Stardust Interstellar Preliminary Examination X: Impact speeds and directions of interstellar grains on the Stardust dust collector. Meteoritics & Planetary Science
[doi:10.1111/maps.12219]
Published by arrangement with John Wiley & Sons

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Maurizio Gemelli, Massimo D’Orazio and Luigi Folco

Dipartimento di Scienze della Terra, Università di Pisa, Pisa, Italy

We evaluate the performance of a hand-held XRF (HHXRF) spectrometer for the bulk analysis of iron meteorites. Analytical precision and accuracy were tested on metal alloy certified reference materials and iron meteorites of known chemical composition. With minimal sample preparation (i.e., flat or roughly polished surfaces) HHXRF allowed the precise and accurate determination of most elements heavier than Mg, with concentrations > 0.01% m/m in metal alloy CRMs, and of major elements Fe and Ni and minor elements Co, P and S (generally ranging from 0.1 to 1% m/m) in iron meteorites. In addition, multiple HHXRF spot analyses could be used to determine the bulk chemical composition of iron meteorites, which are often characterised by sulfide and phosphide accessory minerals. In particular, it was possible to estimate the P and S bulk contents, which are of critical importance for the petrogenesis and evolution of Fe-Ni-rich liquids and iron meteorites. This study thus validates HHXRF as a valuable tool for use in meteoritics, allowing the rapid, non-destructive (a) identification of the extraterrestrial origin of metallic objects (i.e., archaeological artefacts); (b) preliminary chemical classification of iron meteorites; (c) identification of mislabelled/unlabelled specimens in museums and private collections and (d) bulk analysis of iron meteorites.

Reference
Gemelli M, D’Orazio M and Folco L (in press) Chemical Analysis of Iron Meteorites Using a Hand-Held X-Ray Fluorescence Spectrometer. Geostandards and Geoanalytical Research
[doi:10.1111/j.1751-908X.2014.00291.x]
Published by arrangement with John Wiley & Sons

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Andreas Nathues^a et al. (>10)*
*Find the extensive, full author and affiliation list on the publishers website.

^aMax Planck Institute for Solar System Research, Justus-von-Liebig-Weg 3, 37077, Göttingen

The Dawn mission’s Framing Camera (FC) observed asteroid (4) Vesta in 2011 and 2012 using seven color filters and one clear filter from different orbits. In the present paper we analyze recalibrated HAMO color cubes (spatial resolution ∼60 m/pixel) with a focus on Dark Material (DM). We present a definition of highly concentrated DM based on spectral parameters, subsequently map the DM across the Vestan surface, geologically classify DM, study its spectral properties on global and local scales, and finally, compare the FC in-flight color data with laboratory spectra.
We have discovered an absorption band centered at 0.72 μm in localities of DM that show the lowest albedo values by using FC data as well as spectral information from Dawn’s imaging spectrometer VIR. Such localities are contained within impact-exposed outcrops on inner crater walls and ejecta material. Comparisons between spectral FC in-flight data, and laboratory spectra of meteorites and mineral mixtures in the wavelength range 0.4 to 1.0 μm, revealed that the absorption band can be attributed to the mineral serpentine, which is typically present in CM chondrites. Dark material in its purest form is rare on Vesta’s surface and is distributed globally in a non-uniform manner. Our findings confirm the hypothesis of an exogenic origin of the DM by the infall of carbonaceous chondritic material, likely of CM type. It further confirms the hypothesis that most of the DM was deposited by the Veneneia impact.

Reference
Nathues et al. (in press) Detection of Serpentine in Exogenic Carbonaceous Chondrite Material on Vesta from Dawn FC Data. Icarus
[doi:10.1016/j.icarus.2014.06.003]
Copyright Elsevier

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