¹Lisseth Gavilan, ²Laurent Remusat, ²Mathieu Roskosz, ³Horia Popescu, ³Nicolas Jaouen, ⁴Christophe Sandt, ⁵Cornelia Jäger, ⁶Thomas Henning, ⁷Alexandre Simionovici, ⁸Jean Louis Lemaire
The Astrophysical Journal 840, 35 Link to Article [https://doi.org/10.3847/1538-4357/aa6bfc]
¹LATMOS, Université Versailles St Quentin, UPMC Université Paris 06, CNRS, 11 blvd d’Alembert, F-78280 Guyancourt, France
²IMPMC, CNRS UMR 7590; Sorbonne Universités, UPMC Université Paris 06; IRD, Muséum National d’Histoire Naturelle, CP 52, 57 rue Cuvier, Paris F-75231, France
³SEXTANTS beamline, SOLEIL synchrotron, L’Orme des Merisiers, F-91190 Saint-Aubin, France
⁴SMIS beamline, SOLEIL synchrotron, L’Orme des Merisiers, F-91190 Saint-Aubin, France
⁵Laboratory Astrophysics and Cluster Physics Group of the Max Planck Institute for Astronomy at the Friedrich Schiller University & Institute of Solid State Physics, Helmholtzweg 3, D-07743 Jena, Germany
⁶Max-Planck Institute for Astronomy Königstuhl 17, D-69117 Heidelberg, Germany
⁷Institut des Sciences de la Terre, Observatoire des Sciences de l’Univers de Grenoble, BP 53, F-38041 Grenoble, France
⁸Institut des Sciences Moléculaires d’Orsay (ISMO), CNRS, Univ. Paris Sud, Université Paris-Saclay, F-91405 Orsay, France
⁹Institut Jean Lamour, CNRS, Université de Lorraine, F-54011 Nancy, France

The deuterium enrichment of organics in the interstellar medium, protoplanetary disks, and meteorites has been proposed to be the result of ionizing radiation. The goal of this study is to simulate and quantify the effects of soft X-rays (0.1–2 keV), an important component of stellar radiation fields illuminating protoplanetary disks, on the refractory organics present in the disks. We prepared tholins, nitrogen-rich organic analogs to solids found in several astrophysical environments, e.g., Titan’s atmosphere, cometary surfaces, and protoplanetary disks, via plasma deposition. Controlled irradiation experiments with soft X-rays at 0.5 and 1.3 keV were performed at the SEXTANTS beamline of the SOLEIL synchrotron, and were immediately followed by ex-situ infrared, Raman, and isotopic diagnostics. Infrared spectroscopy revealed the preferential loss of singly bonded groups (N–H, C–H, and R–N≡C) and the formation of sp3 carbon defects with signatures at ~1250–1300 cm−1. Raman analysis revealed that, while the length of polyaromatic units is only slightly modified, the introduction of defects leads to structural amorphization. Finally, tholins were measured via secondary ion mass spectrometry to quantify the D, H, and C elemental abundances in the irradiated versus non-irradiated areas. Isotopic analysis revealed that significant D-enrichment is induced by X-ray irradiation. Our results are compared to previous experimental studies involving the thermal degradation and electron irradiation of organics. The penetration depth of soft X-rays in μm-sized tholins leads to volume rather than surface modifications: lower-energy X-rays (0.5 keV) induce a larger D-enrichment than 1.3 keV X-rays, reaching a plateau for doses larger than 5 × 1027 eV cm−3. Synchrotron fluences fall within the expected soft X-ray fluences in protoplanetary disks, and thus provide evidence of a new non-thermal pathway to deuterium fractionation of organic matter.

¹J.B. Creech, ^1,2F. Moynier, ³M. Bizzarro
Geochmica et Cosmochmica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2017.04.040]
¹Institut de Physique du Globe de Paris, Université Sorbonne Paris Cité, Université Paris Diderot, 1 Rue Jussieu, 75328 Paris cedex 05, France
²Institut Universitaire de France, 75005, Paris, France
³Centre for Star and Planet Formation, Natural History Museum of Denmark, University of Copenhagen, Øster Voldgade 5-7, DK-1350 Copenhagen, Denmark
Copyright Elsevier

Stable isotope studies of highly siderophile elements (HSE) have the potential to yield valuable insights into a range of geological processes. In particular, the strong partitioning of these elements into metal over silicates may lead to stable isotope fractionation during metal–silicate segregation, making them sensitive tracers of planetary differentiation processes. We present the first techniques for the precise determination of palladium stable isotopes by MC-ICPMS using a 106Pd–110Pd double-spike to correct for instrumental mass fractionation. Results are expressed as the per mil (‰) difference in the 106Pd/105Pd ratio (δ106Pd) relative to an in-house solution standard (Pd_IPGP) in the absence of a certified Pd isotopic standard. Repeated analyses of the Pd isotopic composition of the chondrite Allende demonstrate the external reproducibility of the technique of ± 0.032‰ on δ106Pd. Using these techniques, we have analysed Pd stable isotopes from a range of terrestrial and extraterrestrial samples. We find that chondrites define a mean δ106Pdchondrite= –0.19 ± 0.05‰ . Ureilites reveal a weak trend towards heavier δ106Pd with decreasing Pd content, similar to recent findings based on Pt stable isotopes (Creech et al., 2017, Geochem. Persp. Let. 3, 94–104), although fractionation of Pd isotopes is significantly less than for Pt, possibly related to its weaker metal–silicate partitioning behaviour and the limited field shift effect. Terrestrial mantle samples have a mean δ106Pdmantle = –0.182 ± 0.130‰ , which is consistent with a late-veneer of chondritic material after core formation.

¹C.R. Kuchka, ¹C.D.K. Herd, ^1,2E.L. Walton, ³Y. Guan, ^3,4Y. Liu
Geochmica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2017.04.037]
¹University of Alberta, Department of Earth and Atmospheric Sciences, Edmonton, AB, T6G 2E3, Canada
²MacEwan University, Department of Physical Sciences, Edmonton, AB T5J 4S2, Canada
³Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125, USA
⁴Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA
Copyright Elsevier

We apply an array of in situ analytical techniques, including electron and Raman microscopy, electron and ion probe microanalysis, and laser ablation mass spectrometry to the Tissint martian meteorite in order to find and elucidate a geochemical signature characteristic of low-temperature alteration at or near the martian surface. Tissint contains abundant shock-produced quench-crystallized melt pockets containing water in concentrations ranging from 73 to 1730 ppm; water content is positively correlated with Cl content. The isotopic composition of hydrogen in the shock-produced glass ranges from δD = 2559 to 4422 ‰. Water is derived from two distinct hydrogen reservoirs: the martian near-surface (>500 ‰) and the martian mantle (-100 ‰). In one shock melt pocket comprising texturally homogeneous vesiculated glass, the concentration of H in the shock melt decreases while simultaneously becoming enriched in D, attributable to the preferential loss of H over D to the vesicle while the pocket was still molten. While igneous sulfides are pyrrhotite in composition (Fe0.88-0.90S), the iron to sulfur ratios of spherules in shock melt pockets are elevated, up to Fe1.70S, which we attribute to shock-oxidation of igneous pyrrhotite and the formation of hematite at high temperature. The D- and Cl-enrichment, and higher oxidation of the pockets (as indicated by hematite) support a scenario in which alteration products formed within fractures or void spaces within the rock; the signature of these alteration products is preserved within shock melt (now glass) which formed upon collapse of these fractures and voids during impact shock. Thermal modeling of Tissint shock melt pockets using the HEAT program demonstrates that the shock melt pockets with the greatest potential to preserve a signature of aqueous alteration are small, isolated from other regions of shock melt, vesicle-free, and glassy.

¹Davide Lenaz,²Birger Schmitz
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12885]
¹Department of Mathematics and Geosciences, University of Trieste, Trieste, Italy
²Division of Nuclear Physics, Department of Physics, Lund University, Lund, Sweden
Published by arrangement with John Wiley & Sons

Six Cr-spinel grains from NWA 6077 brachinite-like and NWA 725 winonaite achondrites have been studied by single-crystal X-ray diffraction and structural refinement. From a chemical point of view, spinels from NWA 6077 show Cr/(Cr + Al) (i.e., Cr#) and Mg/(Mg + Fe2+) (i.e., Mg#) values similar to other brachinites, while the Cr# of NWA 725 is lower than that of literature winonaites. Spinels from NWA 6077 and NWA 725 meteorites show similar cell edges, while the oxygen positional parameter is rather different being about 0.2629 for NWA 6077 and 0.2622 for NWA 725. Considering both parameters, NWA 725 shows structural features that are close to some terrestrial spinel occurrences as in komatiites, kimberlites, or included in diamonds; those from NWA 6077 show values that have no terrestrial analogs. Olivine-chromite closure temperature ranges from ~737 to ~765° C for NWA 725, being similar to that of literature winonaites and ~846 to ~884° C for NWA 6077. The logfO2 ranges from −19.8 to −20.5 and −17.0 to −17.9 for the two meteorites, respectively. The u values for terrestrial samples can give information about the cooling history of the samples. For the extraterrestrial samples, it seems that it can give information about the cooling only for spinels where it is lower than 0.2625. For higher values, it appears related only to the chemistry of the spinels.

¹Dwijesh Ray,²Dewashish Upadhyay,³Saumitra Misra,⁴Horton E. Newsom,¹Sambhunath Ghosh
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12881]
¹Planetary Sciences Division, Physical Research Laboratory, Ahmedabad, India
²Department of Geology and Geophysics, Indian Institute of Technology, Kharagpur, India
³Discipline of Geological Sciences, SAEES, University of KwaZulu-Natal, Durban, South Africa
⁴Institute of Meteoritics and Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque, New Mexico, USA
Published by arrangement with John Wiley & Sons

The Lonar impact crater, India, is one of the few known terrestrial impact craters excavated in continental basaltic target rocks (Deccan Traps, ~65 Ma). The impactites reported from the crater to date mainly include centimeter- to decimeter-sized impact-melt bombs, and aerodynamically shaped millimeter- and submillimeter-sized impact spherules. They occur in situ within the ejecta around the crater rim and show schlieren structure. In contrast, non–in situ glassy objects, loosely strewn around the crater lake and in the ejecta around the crater rim do not show any schlieren structure. These non–in situ fragments appear to be similar to ancient bricks from the Daityasudan temple in the Lonar village. Synthesis of existing and new major and trace element data on the Lonar impact spherules show that (1) the target Lonar basalts incorporated into the spherules had undergone minimal preimpact alteration. Also, the paleosol layer as preserved between the top-most target basalt flow and the ejecta blanket, even after the impact, was not a source component for the Lonar impactites, (2) the Archean basement below the Deccan traps were unlikely to have contributed material to the impactite parental melts, and (3) the impactor asteroid components (Cr, Co, Ni) were concentrated only within the submillimeter-sized spherules. Two component mixing calculations using major oxides and Cr, Co, and Ni suggest that the Lonar impactor was a EH-type chondrite with the submillimeter-sized spherules containing ~6 wt% impactor components.

¹John F. Mustard
Journal of Geophysical Research Planets (in Press) Link to Article [DOI: 10.1002/2017JE005315]
¹Department of Earth, Environmental and Planetary Sciences, Brown University, Providence, Rhode Island, USA
Published by arrangement with John Wiley & Sons

Remotely sensed data and the instruments that acquire them are core parts of Earth and planetary observation systems. They are used to quantify the Earth’s interconnected systems, and remote sensing is the only way to get a daily, or more frequent, snapshot of the status of the Earth. It really is the Earth’s stethoscope. In a similar manner remote sensing is the rock hammer of the planetary scientist and the only way comprehensive data sets can be acquired. To risk offending many remotely sensed data acquired across the electromagnetic spectrum, it is the tricorder to explore known and unknown planets. Arriving where we are today in the use of remotely sensed data in the solar system has been a continually evolving synergy between Earth observation, planetary exploration, and fundamental laboratory work.

¹V.Payré et al. (>10)*
Journal of Geophysical Research Planets (in Press) Link to Article [DOI: 10.1002/2016JE005201]
¹GeoRessources, Université de Lorraine, Nancy, France
*Find the extensive, full author and affiliation list on the publishers website
Published by arrangement with John Wiley & Sons

The Chemistry Camera (ChemCam) instrument onboard Curiosity can detect minor and trace elements such as lithium, strontium, rubidium, and barium. Their abundances can provide some insights about Mars’ magmatic history and sedimentary processes. We focus on developing new quantitative models for these elements by using a new laboratory database (more than 400 samples) that displays diverse compositions that are more relevant for Gale crater than the previous ChemCam database. These models are based on univariate calibration curves. For each element, the best model is selected depending on the results obtained by using the ChemCam calibration targets onboard Curiosity. New quantifications of Li, Sr, Rb, and Ba in Gale samples have been obtained for the first 1000 Martian days. Comparing these data in alkaline and magnesian rocks with the felsic and mafic clasts from the Martian meteorite NWA7533—from approximately the same geologic period—we observe a similar behavior: Sr, Rb, and Ba are more concentrated in soluble- and incompatible-element-rich mineral phases (Si, Al, and alkali-rich). Correlations between these trace elements and potassium in materials analyzed by ChemCam reveal a strong affinity with K-bearing phases such as feldspars, K-phyllosilicates, and potentially micas in igneous and sedimentary rocks. However, lithium is found in comparable abundances in alkali-rich and magnesium-rich Gale rocks. This very soluble element can be associated with both alkali and Mg-Fe phases such as pyroxene and feldspar. These observations of Li, Sr, Rb, and Ba mineralogical associations highlight their substitution with potassium and their incompatibility in magmatic melts.

^1,2Surya S. Rout,^1,2,3Philipp R. Heck,⁴Nestor J. Zaluzec,⁵Takayuki Ishii,⁶Jianguo Wen,⁶Dean J. Miller,^1,7Birger Schmitz
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12887]
¹Robert A. Pritzker Center for Meteoritics and Polar Studies, The Field Museum of Natural History, Chicago, Illinois, USA
²Chicago Center for Cosmochemistry, The University of Chicago, Chicago, Illinois, USA
³Department of the Geophysical Sciences, The University of Chicago, Chicago, Illinois, USA
⁴Photon Science Division, Argonne National Laboratory, Argonne, Illinois, USA
⁵Bayerisches Geoinstitut, University of Bayreuth, Bayreuth, Germany
⁶Electron and X-ray Microscopy, Center for Nanoscale Materials, Argonne National Laboratory, Argonne, Illinois, USA
⁷Astrogeobiology Laboratory, Department of Physics, Lund University, SE, Lund, Sweden
Published by arrangement with John Wiley & Sons

Chromites from Middle Ordovician fossil L chondrites and from matrix and shock-melt veins in Catherwood, Tenham, and Coorara L chondrites were studied using Raman spectroscopy and TEM. Raman spectra of chromites from fossil L chondrites showed similarities with chromites from matrix and shock-melt veins in the studied L chondrite falls and finds. Chromites from shock-melt veins of L chondrites show polycrystallinity, while the chromite grains in fossil L chondrites are single crystals. In addition, chromites from shock-melt veins in the studied L chondrites have high densities of planar fractures within the subgrains and many subgrains show intergrowths of chromite and xieite. Matrix chromite of Tenham has similar dislocation densities and planar fractures as a chromite from the fossil meteorite Golvsten 001 and higher dislocation densities than in chromite from the fossil meteorite Sextummen 003. Using this observation and knowing that the matrix of Tenham experienced 20–22 GPa and <1000° C, an upper limit for the P,T conditions of chromite from Golvsten 001 and Sextummen 003 can be estimated to be 20–22 GPa and 1000° C (shock stage S3–S6) and 20 GPa and 1000° C (S3–S5), respectively, and we conclude that the studied fossil meteorite chromites are from matrix.

^1,2Tuan H. Vu, ^1,2Robert Hodyss, ^1,2Paul V. Johnson, ^1,2Mathieu Choukroun
Planetary and Space Science (in Press) Link to Article [https://doi.org/10.1016/j.pss.2017.04.014]
¹Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California 91109, USA
²NASA Astrobiology Institute

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¹Selby Cull-Hearth, ¹M. Caroline Clark
Planetary and Space Science (in Press) Link to Article [https://doi.org/10.1016/j.pss.2017.03.011]
¹Bryn Mawr College, Bryn Mawr, PA, USA 19010

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