¹Caroline de Beule, ^1,2Joachim Landers, ^1,2Soma Salamon, ^1,2Heiko Wende, ¹Gerhard Wurm
The Astrophysical Journal 837, 59 Link to Article [https://doi.org/10.3847/1538-4357/837/1/59]
¹Faculty of Physics, University of Duisburg-Essen, Lotharstr. 1, D-47057 Duisburg, Germany
²Center for Nanointegration Duisburg-Essen (CENIDE), University of Duisburg-Essen, Carl-Benz-Str. 199, D-47057 Duisburg, Germany

It is an open question how elevated temperatures in the inner parts of protoplanetary disks influence the formation of planetesimals. We approach this problem here by studying the tensile strength of granular beds with dust samples tempered at different temperatures. We find via laboratory experiments that tempering at increasing temperatures is correlated with an increase in cohesive forces. We studied dust samples of palagonite (JSC Mars-1a) which were tempered for up to 200 hr at temperatures between 600 and 1200 K, and measured the relative tensile strengths of highly porous dust layers once the samples cooled to room temperature. Tempering increases the tensile strength from 800 K upwards. This change is accompanied by mineral transformations, the formation of iron oxide crystallites as analyzed by Mössbauer spectroscopy, changes in the number size distribution, and the morphology of the surface visible as cracks in larger grains. These results suggest a difference in the collisional evolution toward larger bodies with increasing temperature as collisional growth is fundamentally based on cohesion. While high temperatures might also increase sticking (not studied here), compositional evolution will already enhance the cohesion and the possibility of growing larger aggregates on the way toward planetesimals. This might lead to a preferred in situ formation of inner planets and explain the observed presence of dense inner planetary systems.

^1,2Julie D. Stopar, ³Bradley L. Jolliff, ¹Emerson J. Speyerer, ¹Erik I. Asphaug, ¹Mark S. Robinson
Planetary and Space Science (in Press) Link to Article [https://doi.org/10.1016/j.pss.2017.05.010]
¹School of Earth and Space Exploration, Arizona State University, Tempe, AZ, USA
²Lunar and Planetary Institute, Houston, TX, USA
³Department of Earth and Planetary Sciences, Washington University in St. Louis, MO, USA

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U.Böttger et al. (>10)*
Planetary and Space Science (in Press) Link to Article [https://doi.org/10.1016/j.pss.2017.05.004]
¹Institute of Optical Sensor Systems, German Aerospace Center (DLR), Rutherfordstr. 2, 12489 Berlin, Germany
*Find the extensive, full author and affiliation list on the publishers website

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¹Hiroki Chihara, ²Chiyoe Koike
Planetary and Space Science (in Press) Link to Article [https://doi.org/10.1016/j.pss.2017.06.003]
¹Department of General Education, Osaka Sangyo University, 3-1-1, Nakagaito, Daito, Osaka 560-0043, Japan
²Department of Science and Engineering, Ritsumeikan University, Japan

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¹Jeremy J. Kent,²Alan D. Brandon,³Katherine H. Joy,⁴Anne H. Peslier,²Thomas J. Lapen,⁵Anthony J. Irving,⁶Daniel M. Coleff
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12898]
¹GeoControl Systems, Jacobs J.E.T.S. Contract, NASA-Johnson Space Center, Houston, Texas, USA
²University of Houston, Department of Earth and Atmospheric Sciences, Houston, Texas, USA
³School of Earth and Environmental Sciences, University of Manchester, Manchester, UK
⁴Jacobs, NASA-Johnson Space Center, Houston, Texas, USA
⁵University of Washington, Department of Earth and Space Sciences, Seattle, Washington, USA
⁶HX5, Jacobs J.E.T.S. Contract, NASA-Johnson Space Center, Houston, Texas, USA
Published by arrangement with john Wiley & Sons

Lunar meteorite Northwest Africa (NWA) 5744 is a granulitic breccia with an anorthositic troctolite composition that may represent a distinct crustal lithology not previously described. This meteorite is the namesake and first-discovered stone of its pairing group. Bulk rock major element abundances show the greatest affinity to Mg-suite rocks, yet trace element abundances are more consistent with those of ferroan anorthosites. The relatively low abundances of incompatible trace elements (including K, P, Th, U, and rare earth elements) in NWA 5744 could indicate derivation from a highlands crustal lithology or mixture of lithologies that are distinct from the Procellarum KREEP terrane on the lunar nearside. Impact-related thermal and shock metamorphism of NWA 5744 was intense enough to recrystallize mafic minerals in the matrix, but not intense enough to chemically equilibrate the constituent minerals. Thus, we infer that NWA 5744 was likely metamorphosed near the lunar surface, either as a lithic component within an impact melt sheet or from impact-induced shock.

¹Alex M. Ruzicka,¹Melinda Hutson,^2,3Jon M. Friedrich,⁴Mark L. Rivers,^3,5Michael K. Weisberg,³Denton S. Ebel,⁶Karen Ziegler,⁷Douglas Rumble III,^2,8Alyssa A. Dolan
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12901]
¹Cascadia Meteorite Laboratory, Department of Geology, Portland State University, Portland, Oregon, USA
²Department of Chemistry, Fordham University, Bronx, New York, USA
³Department of Earth and Planetary Sciences, American Museum of Natural History, New York City, New York, USA
⁴Consortium for Advanced Radiation Sources, University of Chicago, Argonne, Illinois, USA
⁵Department of Physical Sciences, Kingsborough College and Graduate School of the City University of New York, Brooklyn, New York, USA
⁶Institute of Meteoritics, University of New Mexico, Albuquerque, New Mexico, USA
⁷Geophysical Laboratory, Carnegie Institution of Washington, Washington, D.C., USA
⁸Georgetown Law Center, Washington, D.C., USA
Published by arrangement with John Wiley & Sons

Miller Range 07273 is a chondritic melt breccia that contains clasts of equilibrated ordinary chondrite set in a fine-grained (<5 μm), largely crystalline, igneous matrix. Data indicate that MIL was derived from the H chondrite parent asteroid, although it has an oxygen isotope composition that approaches but falls outside of the established H group. MIL also is distinctive in having low porosity, cone-like shapes for coarse metal grains, unusual internal textures and compositions for coarse metal, a matrix composed chiefly of clinoenstatite and omphacitic pigeonite, and troilite veining most common in coarse olivine and orthopyroxene. These features can be explained by a model involving impact into a porous target that produced brief but intense heating at high pressure, a sudden pressure drop, and a slower drop in temperature. Olivine and orthopyroxene in chondrule clasts were the least melted and the most deformed, whereas matrix and troilite melted completely and crystallized to nearly strain-free minerals. Coarse metal was largely but incompletely liquefied, and matrix silicates formed by the breakdown during melting of albitic feldspar and some olivine to form pyroxene at high pressure (>3 GPa, possibly to ~15–19 GPa) and temperature (>1350 °C, possibly to ≥2000 °C). The higher pressures and temperatures would have involved back-reaction of high-pressure polymorphs to pyroxene and olivine upon cooling. Silicates outside of melt matrix have compositions that were relatively unchanged owing to brief heating duration.

¹L. J. Hicks, ¹J. L. Macarthur, ¹J. C. Bridges, ²M. C. Price, ²J. E. Wickham-Eade, ²M. J. Burchell, ¹G. M. Hansford, ³A. L. Butterworth, ¹S. J. Gurman, ¹S. H. Baker
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12909]
¹Department of Physics & Astronomy, Space Research Centre, University of Leicester, Leicester, UK
²School of Physical Sciences, University of Kent, Canterbury, UK
³Space Sciences Laboratory, University of California at Berkeley, Berkeley, California, USA
Published by arrangement with John Wiley & Sons

The mineralogy of comet 81P/Wild 2 particles, collected in aerogel by the Stardust mission, has been determined using synchrotron Fe-K X-ray absorption spectroscopy with in situ transmission XRD and X-ray fluorescence, plus complementary microRaman analyses. Our investigation focuses on the terminal grains of eight Stardust tracks: C2112,4,170,0,0; C2045,2,176,0,0; C2045,3,177,0,0; C2045,4,178,0,0; C2065,4,187,0,0; C2098,4,188,0,0; C2119,4,189,0,0; and C2119,5,190,0,0. Three terminal grains have been identified as near pure magnetite Fe3O4. The presence of magnetite shows affinities between the Wild 2 mineral assemblage and carbonaceous chondrites, and probably resulted from hydrothermal alteration of the coexisting FeNi and ferromagnesian silicates in the cometary parent body. In order to further explore this hypothesis, powdered material from a CR2 meteorite (NWA 10256) was shot into the aerogel at 6.1 km s−1, using a light-gas gun, and keystones were then prepared in the same way as the Stardust keystones. Using similar analysis techniques to the eight Stardust tracks, a CR2 magnetite terminal grain establishes the likelihood of preserving magnetite during capture in silica aerogel.

^1,2Valentin O. Osadchii, ³Mark V. Fedkin, ²Evgeniy G. Osadchii
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12919]
¹Department of Geochemistry, The Faculty of Geology, Moscow State University, Moscow, Russia
²Laboratory of High Temperature Electrochemistry, The Institute of ³Experimental Mineralogy, The Russian Academy of Science, Chernogolovka, Moscow Region, Russia
⁴Department of Mechanical and Nuclear Engineering, The Pennsylvania State University, University Park, Pennyslvania, USA
Published by arrangement with John Wiley & Sons

High-temperature solid-state electrochemistry techniques (EMF method) were used to measure the oxygen fugacity (fO2) of the ordinary chondrites Ochansk (H4), Savtschenskoje (LL4), Elenovka (L5), Vengerovo (H5), and Kharkov (L6). The fO2 results are presented in the form of the following equations:

[not displayed here due to technical reasons]

It was found that fO2 regularly increases from H chondrites to LL chondrites. Measured fO2 are ~1.5 higher than those previously calculated from mineral assemblages. Kharkov (L6) is a little more oxidized than Elenovka (L5) in agreement with the progressive oxidation model. At the same time, Ochansk (H4) is more oxidized than Vengerovo (H5) and exhibits a slightly different slope compared to other chondrites and at T > 1200 K, becomes more reduced than Kharkov (L6) or Elenovka (L5). Measured oxygen fugacity values of meteorites fall within (0.1–1.0)·log fO2 of one another. The possible explanation of discrepancies between measured and calculated values is discussed.

^1,2,3Steven B. Simon, ^1,4Stephen R. Sutton
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12908]
¹Department of the Geophysical Sciences, The University of Chicago, Chicago, Illinois, USA
²The Field Museum of Natural History, Chicago, Illinois, USA
³Institute of Meteoritics, University of New Mexico, Albuquerque, New Mexico, USA
⁴Center for Advanced Radiation Sources (CARS), The University of Chicago, Chicago, Illinois, USA
Published by arrangement with John Wiley & Sons

The valences of Ti, V, and Cr in olivine and pyroxene, important indicators of the fO2 of the source region of their host rocks, can be readily measured nondestructively by XANES (X-ray absorption near edge structure) spectroscopy, but little such work has been done on lunar rocks, and there is some uncertainty regarding the presence of Ti3+ in lunar silicates and the redox state of the lunar mantle. This is the first study involving direct XANES measurement of valences of multivalent cations in lunar rocks. Because high alumina activity facilitates substitution of Ti cations into octahedral rather than tetrahedral sites in pyroxene and Ti3+ only enters octahedral sites, two aluminous basalts from Apollo 14, 14053 and 14072, were studied. Most pyroxene contains little or no detectable Ti3+, but in both samples relatively early, magnesian pyroxene was found that has Ti valences that are not within error of 4; in 14053, this component has an average Ti valence of 3.81 ± 0.06 (i.e., Ti3+/[Ti3+ + Ti4+ = 0.19]). This pyroxene has relatively low atomic Ti/Al ratios (<0.4) due to crystallization before plagioclase, contrary to the long-held belief that lunar pyroxene with Ti/Al > 0.5 contains Ti3+ and pyroxene with lower ratios does not. Later pyroxene, with lower Mg/Fe and higher Ti/Al ratios, has higher proportions of Ti (all Ti4+) in tetrahedral sites. All pyroxene analyzed contains divalent Cr, ranging from 15 to 30% of the Cr present, and all but one analysis spot contains divalent V, accounting for 0 to 40% (typically 20–30%) of the V present. Three analyses of olivine in 14053 do not show any Ti3+, but Ti valences in 14072 olivine range from 4 down to 3.70 ± 0.10. In 14053 olivine, ~50% of the Cr and 60% of the V are divalent. In 14072 olivine, the divalent percentages are ~20% for Cr and 20–60% for V. These results indicate significant proportions of divalent Cr and V and limited amounts of trivalent Ti in the parental melts, especially when crystal/liquid partitioning preferences are taken into account. These features are consistent with an fO2 closer to IW − 2 than to IW − 1. Apollo 15 basalt 15555, analyzed for comparison with A-14 materials, has olivine with strongly reduced Cr (Cr2+/(Cr2+ + Cr3+) ~0.9). Basalts from different sites may record redox differences between source regions.

¹Naotaka Tomioka,²Masaaki Miyahara
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12902]
¹Kochi Institute for Core Sample Research, Japan Agency for Marine-Earth Science and Technology, Nankoku, Kochi, Japan
²Department of Earth and Planetary Systems Science, Graduate School of Science, Hiroshima University, Higashi-Hiroshima, Hiroshima, Japan
Published by arrangement with John Wiley & Sons

Heavily shocked meteorites contain various types of high-pressure polymorphs of major minerals (olivine, pyroxene, feldspar, and quartz) and accessory minerals (chromite and Ca phosphate). These high-pressure minerals are micron to submicron sized and occur within and in the vicinity of shock-induced melt veins and melt pockets in chondrites and lunar, howardite–eucrite–diogenite (HED), and Martian meteorites. Their occurrence suggests two types of formation mechanisms (1) solid-state high-pressure transformation of the host-rock minerals into monomineralic polycrystalline aggregates, and (2) crystallization of chondritic or monomineralic melts under high pressure. Based on experimentally determined phase relations, their formation pressures are limited to the pressure range up to ~25 GPa. Textural, crystallographic, and chemical characteristics of high-pressure minerals provide clues about the impact events of meteorite parent bodies, including their size and mutual collision velocities and about the mineralogy of deep planetary interiors. The aim of this article is to review and summarize the findings on natural high-pressure minerals in shocked meteorites that have been reported over the past 50 years.