^1,2Laurette Piani, ¹Hisayoshi Yurimoto, ³Laurent Remusat
Nature Astronomy 2, 317-323 Link to Article [doi:10.1038/s41550-018-0413-4]
¹Department of Natural History Sciences, Faculty of Science, Hokkaido University, Sapporo, Japan
²CPRG, UMR 7358 CNRS, Université de Lorraine, Vandoeuvre-lès-Nancy, France
³Muséum National d’Histoire Naturelle, Sorbonne Université, UMR CNRS 7590, IRD, Institut de Minéralogie, de Physique des Matériaux et de Cosmochimie, IMPMC, Paris, France

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¹Joseph P. Smith, ²Frank C. Smith, ¹Karl S. Booksh
Applied Spectroscopy 72, 404-419 Link to Article [https://doi.org/10.1177/0003702817721715]
¹Department of Chemistry & Biochemistry, University of Delaware, Newark, DE, USA
²Department of Geological Sciences, University of Delaware, Newark, DE, USA

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^1,2Kathrin Markus, ^1,3Lyuba Moroz, ¹Gabriele Arnold, ^1,4Daniela Henckel, ²Harald Hiesinger, ⁵Arno Rohrbach, ⁵Klemme Stephan
Planetary and Space Science (in Press) Link to Article [https://doi.org/10.1016/j.pss.2018.04.006]
¹DLR, Institut für Planetenforschung, Berlin, Germany
²Institut für Planetologie, Westfälische Wilhelms-Universität Münster, Germany
³Institut für Erd- und Umweltwissenschaften, University of Potsdam, Potsdam, Germany
⁴Institut für Geologische Wissenschaften, Freie Universität Berlin, Germany
⁵Institut für Mineralogie, Westfälische Wilhelms-Universität Münster, Germany

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^1,2D.Perna, ²M.A.Barucci, ²M.Fulchignoni, ^2,3M.Popescu, ^2,4I.Belskaya,²S.Fornasier, ²A.Doressoundiram, ^2,5C.Lantz,²F.Merlin
Planetary and Space Science (in Press) Link to Article [https://doi.org/10.1016/j.pss.2018.03.008]
¹INAF – Osservatorio Astronomico di Roma, Via Frascati 33, 00078 Monte Porzio Catone, Italy
²LESIA – 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
³Astronomical Institute of the Romanian Academy, 5 Cuţitul de Argint, 040557 Bucharest, Romania
⁴Institute of Astronomy, Kharkiv V.N. Karazin National University, Sumska Str. 35, Kharkiv 61022, Ukraine
⁵Institut d’Astrophysique Spatiale, CNRS, UMR-8617, Université Paris-Sud, bâtiment 121, 91405 Orsay, France

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¹A. Gaudin, ^2,3E. Dehouck, ⁴O. Grauby, ¹N. Mangold
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2018.01.029]
¹Laboratoire de Planétologie et Géodynamique de Nantes (LPGN), CNRS/Université de Nantes, 44322 Nantes, France
²IRAP, Université de Toulouse, CNRS, UPS, CNES, Toulouse, France
³Laboratoire de Géologie de Lyon: Terre, Planètes, Environnement, UMR 5276, CNRS, Université Lyon 1, ENS Lyon, Villeurbanne, France
⁴Centre Interdisciplinaire de Nanoscience de Marseille (CINaM), CNRS/Aix-Marseille Université, Campus de Luminy, 13288 Marseille, France
Copyright Elsevier

Laboratory experiments are useful to constrain the environmental parameters that have allowed the formation of the ancient hydrous mineralogical assemblages observed at the surface of Mars, which are dominated by ferric smectites. Weathering under a dense CO2 atmosphere on early Mars is a process frequently invoked to explain their formation, but has proven difficult to test in the laboratory due to low reaction rates. Here, we present a long-term weathering experiment (470 days, at 45°C) of forsteritic olivine specially designed to increase as much as possible the amount of reaction products and thus allow their detailed mineralogical, petrological and chemical characterization by FTIR, SEM and TEM. Our results show the formation of crystalline smectites both under 1 bar of CO2 and under ambient air. However, important differences are observed between the two types of conditions. The smectite formed under CO2 has an average chemical formula per half unit-cell of Si3.92Al0.16Fe3+0.78Mg1.66 Cr0.01Ni0.06K0.04Ca0.04.O10(OH)2. It is thus intermediate between a trioctahedral Mg-rich saponite and a dioctahedral ferric smectite. It is also clearly enriched in Fe compared its counterpart formed under ambient air, which has an average chemical formula per half unit-cell of Si3.68Al0.12Fe3+0.37Mg2.61Cr0.01Ni0.02K0.04Ca0.25.O10(OH)2. This result demonstrates that the enrichment in Fe observed for Martian smectites is to be expected if they were formed by low-temperature weathering under a dense CO2 atmosphere. Another difference is the nature of the accompanying phases, which includes amorphous silica (in the form of opal spheres 10 to 100 nm in diameter) and Mg-carbonates under CO2, but are limited to rare kaolinite under ambient air. The observation of kaolinite particles under air and the significant amount of Al measured in smectites under both atmospheres, despite the Al-poor nature of the initial material, shows that this element is easily concentrated by low-temperature weathering processes. At a larger scale, this concentration mechanism could be responsible for the formation of Al-rich upper horizons, as frequently observed on Mars.

¹G.J. MacPherson, ²C. Defouilloy, ²N.T. Kita
Earth and Planetary Science Letters 491, 238-243 Link to Article [https://doi.org/10.1016/j.epsl.2018.03.039]
¹Dept. of Mineral Sciences, Museum of Natural History, Smithsonian Institution, Washington, DC 20560, USA
²WiscSIMS, Dept. of Geoscience, Univ. of Wisconsin–Madison, Madison, WI 53706, USA
Copyright Elsevier

The Allende CAI View the MathML source is the basis for “ALL”, the lowest measured initial 87Sr/86Sr value in any solar system material including other CAIs (Gray et al., 1973). If the value ALL is correct (debated), then View the MathML source must be 1–2 million years older than other CAIs (Podosek et al., 1991). This would require in turn that it have a much higher initial 26Al/27Al value than other CAIs, on the order of 4 × 10−4. Podosek et al. (1991) showed that this is not the case, with initial 26Al/27Al = (4.5 ± 0.7) × 10−5, but their Mg-isotopic data had large error bars and there was clear isotopic disturbance in the data having the highest 27Al/24Mg. Without the latter data, the slope of their isochron is higher (5.10 ± 1.19) × 10−5) and within (large) error of being supracanonical. We used high-precision SIMS to re-determine the initial 26Al/27Al in this CAI and obtained a value of (5.013 ± 0.099) × 10−5, with an intercept δ26Mg⁎=−0.008±0.048 and MSWD = 1.3. This value is indistinguishable from that measured in many other CAIs and conclusively shows that View the MathML source is not uniquely ancient. We also confirmed evidence of later isotopic disturbance, similar to what Podosek et al. found, indicating a re-melting and evaporation event some 200,000 years after initial CAI solidification.

¹R.C.Oligore
Review of Scientific Instruments 89, 024502 Link to Article [https://aip.scitation.org/doi/10.1063/1.5006261]
¹Physics Department, Washington University in St. Louis, Saint Louis, Missouri 63130, USA

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¹Michael Schäfer et al. (>10)
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13079]
¹Planetary Geology Department, Institute of Planetary Research, German Aerospace Center (DLR), , Berlin, Germany
Published by arrangement with John Wiley & Sons

Ceres’ surface has commonly been linked with carbonaceous chondrites (CCs) by ground‐based telescopic observations, because of its low albedo, flat to red‐sloped spectra in the visible and near‐infrared (VIS/NIR) wavelength region, and the absence of distinct absorption bands, though no currently known meteorites provide complete spectral matches to Ceres. Spatially resolved data of the Dawn Framing Camera (FC) reveal a generally dark surface covered with bright spots exhibiting reflectance values several times higher than Ceres’ background. In this work, we investigated FC data from High Altitude Mapping Orbit (HAMO) and Ceres eXtended Juling (CXJ) orbit (~140 m/pixel) for global spectral variations. We found that the cerean surface mainly differs by spectral slope over the whole FC wavelength region (0.4–1.0 μm). Areas exhibiting slopes <−10% μm−1 constitute only ~3% of the cerean surface and mainly occur in the bright material in and around young craters, whereas slopes ≥−10% μm−1 occur on more than 90% of the cerean surface; the latter being denoted as Ceres’ background material in this work. FC and Visible and Infrared Spectrometer (VIR) spectra of this background material were compared to the suite of CCs spectrally investigated so far regarding their VIS/NIR region and 2.7 μm absorption, as well as their reflectance at 0.653 μm. This resulted in a good match to heated CI Ivuna (heated to 200–300 °C) and a better match for CM1 meteorites, especially Moapa Valley. This possibly indicates that the alteration of CM2 to CM1 took place on Ceres.

¹F.Tosi et al. (>10)
Meteoritisc & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13078]
¹Instituto Nazionale di Astrofisica, Istituto di Astrofisica e Planetologia Spaziali (INAF‐IAPS), , Rome, Italy
Published by arrangement with John Wiley & Sons

We investigate the region of crater Haulani on Ceres with an emphasis on mineralogy as inferred from data obtained by Dawn’s Visible InfraRed mapping spectrometer (VIR), combined with multispectral image products from the Dawn Framing Camera (FC) so as to enable a clear correlation with specific geologic features. Haulani, which is one of the youngest craters on Ceres, exhibits a peculiar “blue” visible to near‐infrared spectral slope, and has distinct color properties as seen in multispectral composite images. In this paper, we investigate a number of spectral indices: reflectance; spectral slopes; abundance of Mg‐bearing and NH4‐bearing phyllosilicates; nature and abundance of carbonates, which are diagnostic of the overall crater mineralogy; plus a temperature map that highlights the major thermal anomaly found on Ceres. In addition, for the first time we quantify the abundances of several spectral endmembers by using VIR data obtained at the highest pixel resolution (~0.1 km). The overall picture we get from all these evidences, in particular the abundance of Na‐ and hydrous Na‐carbonates at specific locations, confirms the young age of Haulani from a mineralogical viewpoint, and suggests that the dehydration of Na‐carbonates in the anhydrous form Na2CO3 may be still ongoing.

^1,2Eva‐Regine Carl, ³Hanns‐Peter Liermann, ^4,5Lars Ehm, ¹Andreas Danilewsky, ¹Thomas Kenkmann
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13077]
¹Institut für Geo‐ und Umweltnaturwissenschaften, Geologie, Albert‐Ludwigs‐Universität, , Freiburg, Germany
²Institut für Geo‐ und Umweltnaturwissenschaften, Kristallographie, Albert‐Ludwigs‐Universität, , Freiburg, Germany
³Photon Science, DESY, , Hamburg, Germany
⁴Mineral Physics Institute, Stony Brook University, Stony Brook, New York, USA
⁵National Synchrotron Light Source II, Brookhaven National Laboratory, Upton, New York, USA
Published by arrangement with John Wiley & Sons

Coesite and stishovite are high‐pressure silica polymorphs known to have been formed at several terrestrial impact structures. They have been used to assess pressure and temperature conditions that deviate from equilibrium formation conditions. Here we investigate the effects of nonhydrostatic, dynamic stresses on the formation of high‐pressure polymorphs and the amorphization of α‐quartz at elevated temperatures. The obtained disequilibrium states are compared with those predicted by phase diagrams derived from static experiments under equilibrium conditions. We analyzed phase transformations starting with α‐quartz in situ under dynamic loading utilizing a membrane‐driven diamond anvil cell. Using synchrotron powder X‐ray diffraction, the phase transitions of SiO₂ are identified up to 77.2 GPa and temperatures of 1160 K at compression rates ranging between 0.10 and 0.37 GPa s⁻¹. Coesite starts forming above 760 K in the pressure range between 2 and 11 GPa. At 1000 K, coesite starts to transform to stishovite. This phase transition is not completed at 1160 K in the same pressure range. Therefore, the temperature initiates the phase transition from α‐quartz to coesite, and the transition from coesite to stishovite. Below 1000 K and during compression, α‐quartz becomes amorphous and partially converts to stishovite. This phase transition occurs between 25 and 35 GPa. Above 1000 K, no amorphization of α‐quartz is observed. High temperature experiments reveal the strong thermal dependence of the formation of coesite and stishovite under nonhydrostatic and disequilibrium conditions.