^1,2Cristobal Petrovich, ³Diego J. Muñoz
The Astrophysical Journal 834, 116  Link to Article [http://dx.doi.org/10.3847/1538-4357/834/2/116]
¹Canadian Institute for Theoretical Astrophysics, University of Toronto, 60 St George Street, ON M5S 3H8, Canada
²Centre for Planetary Sciences, Department of Physical & Environmental Sciences, University of Toronto at Scarborough, Toronto, Ontario M1C 1A4, Canada
³Cornell Center for Astrophysics and Planetary Science, Department of Astronomy, Cornell University, Ithaca, NY 14853, USA

The presence of a planetary system can shield a planetesimal disk from the secular gravitational perturbations due to distant outer massive objects (planets or stellar companions). As the host star evolves off the main sequence to become a white dwarf, these planets can be engulfed during the giant phase, triggering secular instabilities and leading to the tidal disruptions of small rocky bodies. These disrupted bodies can feed the white dwarfs with rocky material and possibly explain the high-metallicity material in their atmospheres. We illustrate how this mechanism can operate when the gravitational perturbations are due to the KL mechanism from a stellar binary companion, a process that is activated only after the planet has been removed/engulfed. We show that this mechanism can explain the observed accretion rates if: (1) the planetary engulfment happens rapidly compared to the secular timescale, which is generally the case for wide binaries ($\gt 100$ au) and planetary engulfment during the asymptotic giant branch; (2) the planetesimal disk has a total mass of $\sim {10}^{-4}-{10}^{-2}{M}_{\oplus }$. We show that this new mechanism can provide a steady supply of material throughout the entire life of the white dwarfs for all cooling ages and can account for a large fraction (up to nearly half) of the observed polluted white dwarfs.

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.