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.