¹G. Micca Longo, ²S. Longo
International Journal of Astrobiology (in Press) Link to Article [DOI: https://doi.org/10.1017/S1473550416000495]
¹Department of Chemistry, University of Bari, via Orabona 4, 70126 Bari, Italy
²CNR-Nanotec, via Amendola 122/D, 70126 Bari, Italy

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¹Carl Melis, ²P. Dufour
The Astrophysical journal (in Press) Link to Article [http://dx.doi.org/10.3847/1538-4357/834/1/1]
¹Center for Astrophysics and Space Sciences, University of California, San Diego, CA 92093-0424, USA
²Institut de Recherche sur les Exoplanètes (iREx), Université de Montréal, Montréal, QC H3C 3J7, Canada

We present spectroscopic observations of the dust- and gas-enshrouded, polluted, single white dwarf star SDSS J104341.53+085558.2 (hereafter SDSS J1043+0855). Hubble Space Telescope Cosmic Origins Spectrograph far-ultraviolet spectra combined with deep Keck HIRES optical spectroscopy reveal the elements C, O, Mg, Al, Si, P, S, Ca, Fe, and Ni and enable useful limits for Sc, Ti, V, Cr, and Mn in the photosphere of SDSS J1043+0855. From this suite of elements we determine that the parent body being accreted by SDSS J1043+0855 is similar to the silicate Moon or the outer layers of Earth in that it is rocky and iron-poor. Combining this with comparison to other heavily polluted white dwarf stars, we are able to identify the material being accreted by SDSS J1043+0855 as likely to have come from the outermost layers of a differentiated object. Furthermore, we present evidence that some polluted white dwarfs (including SDSS J1043+0855) allow us to examine the structure of differentiated extrasolar rocky bodies. Enhanced levels of carbon in the body polluting SDSS J1043+0855 relative to the Earth–Moon system can be explained with a model where a significant amount of the accreted rocky minerals took the form of carbonates; specifically, through this model the accreted material could be up to 9% calcium-carbonate by mass.

¹A.Kereszturi, ²I. Gyollai, ³S. Jozsa, ⁴Z. Kanuchova
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12802]
¹Konkoly Astronomical Institute, Research Centre for Astronomy and Earth Sciences, Budapest, Hungary
²Institute for Geological and Geochemical Research, Research Centre for Astronomy and Earth Sciences, Budapest, Hungary
³Faculty of Science, Department of Petrology and Geochemistry, Hungarian Academy of Sciences, Eotvos Lorand University of Sciences, Budapest, Hungary
⁴Astronomical Institute of Slovak Academy of Sciences, T. Lomnica, Slovakia
Published by arrangement with John Wiley & Sons

The NWA 5491 CV3 meteorite is a CVoxA subtype, and composed of two substantially different units (titled “upper” and “lower” units) in the cm size range with original accreted material and also subsequent alteration produced features. Based on the large chondrules in the “upper” unit and the small chondrules plus CAIs in the “lower” unit, they possibly accreted material from different parts of the solar nebula and/or at different times, whereas substantial changes happened in the nebula’s composition. Differences are observed in the level of early fragmentation too, which was stronger in the upper units. During later alteration oxidizing fluids possibly circulated only in the upper unit, mechanical fragmentation and resorption were also stronger there. In the last phase of the geological history these two rock units came into physical contact, but impact-driven shock effects were not observed. The characteristics of this meteorite provide evidence that the same parent body might accrete substantially different material and also the later processes could differ spatially in the parent body.

¹W. M. Farrell, ²D. M. Hurley, ³V. J. Esposito, ⁴J. L. McLain, ²M. I. Zimmerman
Journal of Geophysical Research (Planets) Link to Article [DOI: 10.1002/2016JE005168]
¹NASA/Goddard Space Flight Center, Greenbelt, MD, USA
²Johns Hopkins University/Applied Physics Laboratory, Laurel, MD, USA
³NASA Goddard Summer Intern Program, NASA/Goddard Space Flight Center, Greenbelt, MD, USA
⁴University of Maryland, College Park, MD, USA
Published by arrangement with John Wiley & Sons

We present a new formalism to describe the outgassing of hydrogen initially implanted by the solar wind protons into exposed soils on airless bodies. The formalism applies a statistical mechanics approach similar to that applied recently to molecular adsorption onto activated surfaces. The key element enabling this formalism is the recognition that the inter-atomic potential between the implanted H and regolith-residing oxides is not of singular value, but possess a distribution of trapped energy values at a given temperature, F(U, T). All subsequent derivations of the outward diffusion and H retention rely on the specific properties of this distribution. We find that solar wind hydrogen can be retained if there are sites in the implantation layer with activation energy values exceeding 0.5 eV. We especially examine the dependence of H retention applying characteristic energy values found previously for irradiated silica and mature lunar samples. We also apply the formalism to two cases that differ from the typical solar wind implantation at the Moon. First, we test for a case of implantation in magnetic anomaly regions where significantly lower energy ions of solar wind origin are expected to be incident with the surface. In magnetic anomalies, H retention is found to be reduced due to the reduced ion flux and shallower depth of implantation. Second, we also apply the model to Phobos where the surface temperature range is not as extreme as the Moon. We find the H atom retention in this second case is higher than the lunar case due to the reduced thermal extremes (that reduces outgassing).

^1,4Chloë E. Bonamici ¹William S. Kinman, ²John H. Fournelle, ^1,5Mindy M. Zimmer, ¹Anthony D. Pollington, ³Kirk D. Rector
Contributions to Mineralogy and Petrolology 172, 2 Link to Article [doi:10.1007/s00410-016-1320-2]
¹Nuclear and Radiochemistry Group, Chemistry Division, Los Alamos National Laboratory, Los Alamos, USA
²Department of Geoscience, University of Wisconsin-Madison, Madison, USA
³Physical Chemistry and Applied Spectroscopy Group, Chemistry Division, Los Alamos National Laboratory, Los Alamos, USA
⁴Department of Earth and Environmental Science, New Mexico Tech, Socorro, USA
⁵Pacific Northwest National Laboratory, Richland, USA

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¹Yanhao Lin, ¹Elodie J. Tronche, ¹Edgar S. Steenstra, ¹Wim van Westrenen
Nature Geoscience 10, 14-18 Link to Article [doi:10.1038/ngeo2845]
¹Faculty of Earth and Life Sciences, VU Amsterdam, De Boelelaan 1085, 1081 HV Amsterdam, The Netherlands

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^1,2Olivier Namur, ¹Bernard Charlier
Nature Geoscience 10, 9-13 Link to Article [doi:10.1038/ngeo2860]
¹Leibniz University Hannover, Institute of Mineralogy, 30167 Hannover, Germany
²University of Liège, Department of Geology, 4000 Sart-Tilman, Belgium

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¹Kevin M. Cannon, ¹John F. Mustard, ¹Stephen W. Parman, ²Elizabeth C. Sklute, ²M. Darby Dyar, ¹Reid F. Cooper
Journal of Geophysical Research Planets (in Press) Link to Article [DOI: 10.1002/2016JE005219]
¹Department of Earth, Environmental and Planetary Sciences, Brown University, Providence, RI, USA
²Mount Holyoke College, South Hadley, MA, USA
Published by arrangement with John Wiley & Sons

Thirty silicate glasses were synthesized as realistic analogs to those expected to exist on Mars, the Moon and Mercury. Samples were measured using visible/near-infrared and Mössbauer spectroscopy to determine the effects of varying bulk chemistry, oxygen fugacity, and temperature on spectral properties. For martian glasses, the fO2 during fusion strongly affects absorption band intensities in the spectra, while bulk chemistry has noticeable secondary effects on absorption band positions. Titanium and iron content drive spectral changes in lunar glasses, where Fe3+ is effectively absent. Iron-free Mercury-analog glasses have much higher albedos than all other samples, and their spectral shape is a close match to some pyroclastic deposits on Mercury. Synthetic glass spectra were used as inputs into a spectral unmixing model applied to remote orbital datasets to test for the presence of glass. The model is validated against physical laboratory mixture spectra, as well as previous detections of glass-rich pyroclastic deposits on the Moon. Remote data were then used from suspected impact deposits and possible pyroclastic deposits on Mars as a new application of the model: the results reveal spatially coherent glass-rich material, and the strong spectral match of the synthetic glasses to these remotely sensed data gives new insights into the presence and character of glasses on the martian surface. The large library of glass spectra generated here, acquired from consistently synthesized and measured samples, can serve as a resource for further studies of volcanic and impact processes on planetary bodies.

¹Andrew W. Beck, ¹David J. Lawrence, ¹Patrick N. Peplowski, ¹Christina E. Viviano-Beck, ²Thomas H. Prettyman, ³Timothy J. McCoy, ⁴Harry Y. McSween Jr, ²Naoyuki Yamashita
Icarus (in Press) Link to Article [http://dx.doi.org/10.1016/j.icarus.2017.01.008]
¹The Johns Hopkins University Applied Physics Laboratory, Laurel, Maryland, 20723, USA
²Planetary Science Institute, Tucson, Arizona, 85719, USA
³Department of Mineral Sciences, Smithsonian Institution, Washington, District of Columbia, 20560, USA
⁴Department of Earth and Planetary Sciences, Knoxville, Tennessee, 37996-1410, USA
Copyright Elsevier

We use data collected by the Dawn Gamma-Ray and Neutron Detector (GRaND) at Vesta to map compositions corresponding to nearly pure igneous lithologies in the howardite, eucrite, diogenite (HED) meteorite clan (samples likely from Vesta). At the ∼300-km spatial scale of GRaND measurements, basaltic eucrite occurs on only 3% of the surface, whereas cumulate eucrite and orthopyroxenitic diogenite are not detected. The basaltic eucrite region is generally coincident with an area of the surface with thick regolith, elevated H, and moderate crater density, and may represent the best compositional sample of primordial vestan crust. We observe an absence of pure orthopyroxenitic diogenite terrains in the Rheasilvia basin and its ejecta, an observation corroborated by VIR (0.1%), which suggests the south-polar crust was a polymict mixture of igneous lithologies (howardite) at the time of the Rheasilvia impact, or was a thick basaltic eucrite crust with heterogeneously distributed orthopyroxenitic diogenite plutons. The most dominant igneous composition detected (11% of the surface) corresponds to one of the least-abundant igneous lithologies in the HED meteorite collection, the Yamato Type B diogenites (plagioclase-bearing pyroxenites). The distribution of Type B diogenite is spatially correlated with post-Rheasilvia craters in the north-polar region that are in close proximity to the Rheasilvia basin antipode. This suggests that north-polar Type B plutonism may have been associated with the Rheasilvia impact event. We propose that this was either through 1) uplift of pre-existing plutons at the antipode through focusing of Rheasilvia impact stress, or 2) Rheasilvia impact antipodal crustal melting, creating magmas that underwent fractionation to produce Type B plutons.

^1,2Jon M. Friedrich, ³Alex Ruzicka, ^5,6Robert J. Macke, ⁴James O. Thostenson, ⁴Rebecca A. Rudolph, ⁵Mark L. Rivers, ^2,7,8Denton S. Ebel
Geochimica et Cosmochimica Acta (in Press) Link to Article [http://dx.doi.org/10.1016/j.gca.2016.12.039]
¹Department of Chemistry, Fordham University, Bronx, NY 10458, USA
²Department of Earth and Planetary Sciences, American Museum of Natural History, New York, NY 10024, USA
³Cascadia Meteorite Laboratory, Portland State University, Department of Geology, Portland, OR 97207-0751, USA
⁴Microscopy and Imaging Facility, American Museum of Natural History, New York, NY 10024, USA
⁵Center for Advanced Radiation Sources, University of Chicago, Argonne, IL 60439, USA
⁶Vatican Observatory, V-00120 Vatican City-State
⁷Lamont-Doherty Earth Observatory, Columbia University, Palisades, New York 10964, USA
⁸Graduate Center of the City University of New York, New York 10016, USA
Copyright Elsevier

Collisions and attendant shock compaction must have been important for the accretion and lithification of planetesimals, including the parent bodies of chondrites, but the conditions under which these occurred are not well constrained. A simple model for the compaction of chondrites predicts that shock intensity as recorded by shock stage should be related to porosity and grain fabric. To test this model, we studied sixteen ordinary chondrites of different groups (H, L, LL) using X-ray computed microtomography (μCT) to measure porosity and metal fabric, ideal gas pycnometry and 3D laser scanning to determine porosity, and optical microscopy (OM) to determine shock stage. These included a subsample of six chondrites previously studied using transmission electron microscopy (TEM) to characterize microstructures in olivine. Combining with previous data, results support the simple model in general, but not for chondrites with low shock-porosity-foliation (low-SPF chondrites). These include Kernouvé (H6), Portales Valley (H6/7), Butsura (H6), Park (L6), GRO 85209 (L6), Estacado (H6), MIL 99301 (LL6), Spade (H6), and Queen’s Mercy (H6), among others. The data for these meteorites are best explained by high ambient heat during or after shock. Low-SPF chondrites tend to have older 40Ar/39Ar ages (∼4435-4526 Ma) than other, non-low-SPF type 6 chondrites in this study. We conclude that the H, L, and LL asteroids all were shock-compacted at an early stage while warm, with collisions occurring during metamorphic heating of the parent bodies. Results ultimately bear on whether chondrite parent bodies have internal structures more akin to a metamorphosed onion shell or metamorphosed rubble pile, and on the nature of accretion and lithification processes for planetesimals.