^1,2Philip R. Heck et al. (>10)
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13129]
¹Department of Science and Education, Robert A. Pritzker Center for Meteoritics and Polar Studies, The Field Museum of Natural History, Chicago, Illinois, USA
²Chicago Center for Cosmochemistry and Department of the Geophysical Sciences, The University of Chicago, Chicago, Illinois, USA
Published by Arrangement with John Wiley & Sons

We present He and Ne isotopes of individual presolar graphite grains from a low‐density separate from Orgueil. Two grain mounts were analyzed with the same techniques but in a different sequence: The first one was measured with NanoSIMS followed by noble gas mass spectrometry, and the second one in reverse order. No grain contained 4He and only one grain on the second mount contained 3He. On the first mount, the grains had been extensively sputtered with NanoSIMS ion beams prior to noble gas analysis; we found only one grain out of 15 with presolar 22Ne above detection limit. In contrast, we found presolar 22Ne in six out of seven grains on the second mount that was not exposed to an ion beam prior to noble gas analysis. All 22 grains on the two mounts were imaged with scanning electron microscopy (SEM) and/or Auger microscopy. We present evidence that this contrasting observation is most likely due to e‐beam–induced heating of the generally smaller grains on the first mount during SEM and Auger imaging, and not primarily due to the NanoSIMS analysis. If thermal contact of the grains to the substrate is absent, such that heat can only be dissipated via radiation, then the smaller, sputter‐eroded grains are heated to higher temperatures such that noble gases can diffuse out. We discuss possible gas loss mechanisms and suggest solutions to reduce heating during e‐beam analyses by minimizing voltages, beam currents, and dwell times. We also found small amounts of 21Ne in five grains. Using isotope data we determined that the dominant sources of most grains are core‐collapse supernovae, congruent with earlier studies of low‐density presolar graphite from Murchison. Only two of the grains are most likely from AGB stars, and two others have an ambiguous origin.

¹Clément Ganino,^2,3Guy Libourel,⁴Akiko M. Nakamura,⁵Suzanne Jacomet,⁶Olivier Tottereau,²Patrick Michel
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13131]
¹Université Côte d’Azur, OCA, CNRS, Géoazur, Sophia‐Antipolis, Valbonne, France
²Université Côte d’Azur, OCA, CNRS, Lagrange, Boulevard de l’Observatoire, Nice Cedex 4, France
³Hawai’i Institute of Geophysics and Planetology, School of Ocean, Earth Science and Technology, University of Hawai’i at MānoaHonolulu, Hawai’i, USA
⁴Graduate School of Science, Kobe University, Kobe, Japan
⁵MINES ParisTech, PSL—Research University, CEMEF—Centre de mise en forme des matériaux, CNRS, UMR 7635Sophia‐Antipolis, France
⁶CRHEA, CNRS UPR 10Sophia Antipolis, France
Published by Arrangement with John Wiley & Sons

Hypervelocity impacts are common in the solar system, in particular during its early phases when primitive bodies of contrasted composition collided. Whether these objects are chemically modified during the impact process, and by what kind of processes, e.g., chemical mixing or gas–liquid–solid fractionation, are still pending questions. To address these issues, a set of impact experiments involving a multielemental doped phonolitic projectile and a metallic target was performed in a 3–7 km s−1 range of impact speeds which are typical of those occurring in the asteroid belt. For each run, both texture and chemistry of the crater and the ejecta population have been characterized. The results show that the melted projectiles largely cover the craters at all speeds, and that melted phonolitic materials are injected into fractures in the crater in the metallic target. Ejecta are generally quenched droplets of silicate impact melt containing metal beads. Some of these beads are extracted from the target, but we propose that some of the Fe metal beads are the result of reduction of FeO. A thin FeO‐SiO2‐rich condensate layer is found at the edge of the crater, suggesting that a limited amount of vapor formed and condensed. LA‐ICP‐MS analyses suggest, however, that within analytical uncertainties, no volatility‐controlled chemical fractionation of trace elements occurred in the ejecta. The main chemical fractionation during impact at such velocities and energies are the result of projectile‐target mixing.

¹Daniele Fulvio, ²Simone Ieva, ^2,3Davide Perna, ⁴Zuzana Kanuchova, ²Elena Mazzotta Epifani, ²Elisabetta Dotto
Planetary and Space Science (in Press) Link to Article [https://doi.org/10.1016/j.pss.2018.06.006]
¹Departamento de Física, Pontifícia Universidade Católica Do Rio de Janeiro, Rua Marquês de São Vicente 225, 22451-900, Rio de Janeiro, RJ, Brazil
²INAF–Osservatorio Astronomico di Roma, Via Frascati 33, Monte Porzio Catone, I-00078, Roma, Italy
³LESIA – Observatoire de Paris, PSL Research University, CNRS, Sorbonne Universités, UPMC Univ. Paris 06, Univ. Paris Diderot, Sorbonne Paris Cité, 5 Place Jules Janssen, 92195, Meudon, France
⁴Astronomical Institute of the Slovak Academy of Sciences, 059 60, Tatranská Lomnica, Slovakia

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¹E.Hadamcik, ²J.Lasue, ³A.C.Levasseur-Regourd, ⁴J.-B.Renard
Planetary and Space Science (in Press) Link to Article [https://doi.org/10.1016/j.pss.2018.04.022]
¹LATMOS-IPSL, 11 bld d’Alembert, 78280 Guyancourt, France
²IRAP, Université de Toulouse, CNES, CNRS, UPS, Toulouse, France
³Sorbonne Université, CNRS-INSU, LATMOS-IPSL, Campus Pierre et Marie Curie, 4 Place Jussieu, 75005 Paris, France
⁴LPC2E-CNRS, Université d’Orléans, 3A Avenue de la Recherche Scientifique, F-45071 Orléans-cedex 2, France

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¹David V. Bekaert, ²Sylvie Derenne, ¹Laurent Tissandier, ¹Yves Marrocchi, ³Sebastien Charnoz, ²Christelle Anquetil, ¹Bernard Marty
The Astrophysical Journal (in Press) Link to Article [https://doi.org/10.3847/1538-4357/aabe7a]
¹Centre de Recherches Pétrographiques et Géochimiques, UMR 7358 CNRS—Université de Lorraine, 15 rue Notre Dame des Pauvres, BP 20, F-54501 Vandoeuvre-lès-Nancy, France
²METIS, UMR CNRS 7619, EPHE-Sorbonne Université, 4 Place Jussieu, F-75252 Paris Cedex 05, France
³Institut de Physique du Globe/Universite Paris Diderot/CEA/CNRS, F-75005 Paris, France

Biologically relevant molecules (hereafter biomolecules) have been commonly observed in extraterrestrial samples, but the mechanisms accounting for their synthesis in space are not well understood. While electron-driven production of organic solids from gas mixtures reminiscent of the photosphere of the protosolar nebula (PSN; i.e., dominated by CO–N2–H2) successfully reproduced key specific features of the chondritic insoluble organic matter (e.g., elementary and isotopic signatures of chondritic noble gases), the molecular diversity of organic materials has never been investigated. Here, we report that a large range of biomolecules detected in meteorites and comets can be synthesized under conditions typical of the irradiated gas phase of the PSN at temperatures = 800 K. Our results suggest that organic materials—including biomolecules—produced within the photosphere would have been widely dispersed in the protoplanetary disk through turbulent diffusion, providing a mechanism for the distribution of organic meteoritic precursors prior to any thermal/photoprocessing and subsequent modification by secondary parent body processes. Using a numerical model of dust transport in a turbulent disk, we propose that organic materials produced in the photosphere of the disk would likely be associated with small dust particles, which are coupled to the motion of gas within the disk and therefore preferentially lofted into the upper layers of the disk where organosynthesis occurs.

¹Gordon Peter R., ¹Sephton Mark A.
Astrobiology 18, 5 Link to Article [https://doi.org/10.1089/ast.2017.1744]
¹Impacts and Astromaterials Research Centre, Department of Earth Science and Engineering, Imperial College London, UK

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¹Jennifer L. Eigenbrode et al. (>10)
Science 360, 1096-1101 Link to Article [DOI: 10.1126/science.aas9185]
¹1Solar System Exploration Division, NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA.
Reprinted with permission from AAAS

Establishing the presence and state of organic matter, including its possible biosignatures, in martian materials has been an elusive quest, despite limited reports of the existence of organic matter on Mars. We report the in situ detection of organic matter preserved in lacustrine mudstones at the base of the ~3.5-billion-year-old Murray formation at Pahrump Hills, Gale crater, by the Sample Analysis at Mars instrument suite onboard the Curiosity rover. Diverse pyrolysis products, including thiophenic, aromatic, and aliphatic compounds released at high temperatures (500° to 820°C), were directly detected by evolved gas analysis. Thiophenes were also observed by gas chromatography–mass spectrometry. Their presence suggests that sulfurization aided organic matter preservation. At least 50 nanomoles of organic carbon persists, probably as macromolecules containing 5% carbon as organic sulfur molecules.

¹Edward A.Cloutis, ²Vishnu Reddy, ³David T.Blewett
Icarus 311, 384-393 Link to Article [https://doi.org/10.1016/j.icarus.2018.04.027]
¹Department of Geography, University of Winnipeg, 515 Portage Avenue, Winnipeg, MB R3B 2E9, Canada
²Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ, USA
³Planetary Exploration Group, Johns Hopkins Applied Physics Laboratory, Laurel, MD, USA
Copyright Elsevier

We have measured reflectance spectra (0.35–25.0 µm) of different size powders of the ungrouped achondrite NWA 7325 in order to facilitate spectroscopic identification of its parent body. Previous work has suggested that the meteorite may have come from the planet Mercury based on its oxidation state. The 0.35–2.5 µm reflectance spectra of NWA 7325 exhibit absorption bands that can be attributed to the presence of chromium-bearing diopside and possibly to Ca-rich plagioclase. Spectral evidence for olivine is generally lacking, likely due to interference from stronger diopside absorption bands. With increasing grain size, albedo decreases while absorption band depths increase. The absorption bands are unique in the sense that they allow for the identification of the Cr-rich diopside in NWA 7325. The mid-infrared spectra are similar to those measured by previous investigators, and enable detection of the major silicates in NWA 7325, including more robust identification of olivine and plagioclase feldspar. We find no spectroscopic or compositional evidence supporting a link to Mercury as a possible parent body, even accounting for plausible spectrum-altering processes. In terms of a link to an asteroidal parent body, the most confident link would be made based on the unique Cr-diopside-related absorption bands in the 0.65, 1.05, and 2.3 µm regions. At present, the closest spectral match we have found is with asteroid 10,537 (1991 RY16).

¹Yves Marrocchi, ¹Johan Villeneuve, ²Valentina Batanova, ¹Laurette Piani, ³Emmanuel Jacquet
Earth and Planetary Science Letters 496, 132-141 Link to Article [https://doi.org/10.1016/j.epsl.2018.05.042]
¹CRPG, CNRS, Université de Lorraine, UMR 7358, Vandoeuvre-lès-Nancy, 54501, France
²Université Grenoble Alpes, ISTerre, CNRS, UMR 5275, Grenoble, F-38000, France
³IMPMC, CNRS & Muséum national d’Histoire naturelle, UMR 7590, CP52, 57 rue Cuvier, 75005 Paris, France
Copyright Elsevier

FeO-poor (type I) porphyritic chondrules formed by incomplete melting of solid dust precursors via a yet-elusive mechanism. Two settings are generally considered for their formation: (i) a nebular setting where primordial solids were melted, e.g. by shock waves propagating through the gas and (ii) a collisional planetary setting. Here we report a method combining high-current electron microprobe X-ray mapping and quantitative measurements to determine the chemical characteristics of relict olivine grains inherited from chondrule precursors. We find that these olivine crystals are Ca–Al–Ti-poor relative to host olivine crystals. Their variable Δ17Δ17O, even in individual chondrule, is inconsistent with derivation from planetary interiors as previously argued from 120 ° triple junctions also exhibited by the chondrules studied herein. This indicates that chondrule precursors correspond to solid nebular condensates formed under changing physical conditions.
We propose that porphyritic chondrules formed during gas-assisted melting of nebular condensates comprising relict olivine grains with varying Δ17Δ17O values and Ca–Al–Ti-rich minerals such as those observed within amoeboid olivine aggregates. Incomplete melting of chondrule precursors produced Ca–Al–Ti-rich melts (CAT-melts), allowing subsequent crystallization of Ca–Al–Ti-rich host olivine crystals via epitaxial growth on relict olivine grains. Incoming MgO and SiO from the gas phase induced (i) the dilution of CAT-melts, as attested by the positive Al–Ti correlation observed in chondrule olivine crystals, and (ii) buffering of the O-isotope compositions of chondrules, as recorded by the constant Δ17Δ17O values of host olivine grains. The O-isotopic compositions of host olivine grains are chondrule-specific, suggesting that chondrules formed in an array of environments of the protoplanetary disk with different Δ17Δ17O values, possibly due to variable solid/gas mixing ratios.

¹Gioacchino Tempesta, ²Giorgio S.Senesi, ³Paola Manzari, ¹Giovanna Agrosì
Spectrochimica Acta Part B: Atomic Spectroscopy 144, 75-81 Link to Article [https://doi.org/10.1016/j.sab.2018.03.014]
¹Dipartimento di Scienze della Terra e Geoambientali (DiSTeGeo), University of Bari, Via E. Orabona 4, 70125 Bari, Italy
²CNR – Istituto di Nanotecnologia (NANOTEC), PLasMI Lab, Via Amendola 122/D, 70126 Bari, Italy
³Istituto Nazionale di Astrofisica, Istituto di Astrofisica e Planetologia Spaziali (INAF-IAPS), via Fosso del Cavaliere 100, Roma, Italy

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