¹F.G. Carrozzo, ²G. Di Achille, ³F. Salese, ¹F. Altieri, ¹G. Bellucci
Icarus (in Press) Link to Article [http://dx.doi.org/10.1016/j.icarus.2016.09.001]
¹Istituto di Astrofisica e Planetologia Spaziali, INAF, Rome, Italy
²Osservatorio Astronomico di Teramo, INAF, Teramo, Italy
³International Research School of Planetary Sciences, Dipartimento di Ingegneria e Geologia, Università Gabriele D’Annunzio, Pescara, Italy
Copyright Elsevier

A variety of hydrothermal environments have been documented in terrestrial impact structures. Due to both past water interactions and meteoritic bombardment on the surface of Mars, several authors have predicted various scenarios that include the formation of hydrothermal systems. Geological and mineralogical evidence of past hydrothermal activity have only recently been found on Mars. Here, we present a geological and mineralogical study of the Auki Crater using the spectral and visible imagery data acquired by the CRISM (Compact Reconnaissance Imaging Spectrometer for Mars), CTX (Context Camera) and HiRISE (High Resolution Imaging Science Experiment) instruments on board the NASA MRO mission.

The Auki Crater is a complex crater that is ∼38 km in diameter located in Tyrrhena Terra (96.8°E and 15.7°S) and shows a correlation between its mineralogy and morphology. The presence of minerals, such as smectite, silica, zeolite, serpentine, carbonate and chlorite, associated with morphological structures, such as mounds, polygonal terrains, fractures and veins, suggests that the Auki Crater may have hosted a post impact-induced hydrothermal system. Although the distribution of hydrated minerals in and around the central uplift and the stratigraphic relationships of some morphological units could also be explained by the excavation and exhumation of carbonate-rich bedrock units as a consequence of crater formation, we favor the hypothesis of impact-induced hydrothermal circulation within fractures and subsequent mineral deposition. The hydrothermal system could have been active for a relatively long period of time after the impact, thus producing a potential transient habitable environment.

¹M. Nachon et al. (>10)*
Icarus (in Press) Link to Article [http://dx.doi.org/10.1016/j.icarus.2016.08.026]
¹Laboratoire de Planétologie et Géodynamique de Nantes, CNRS, UMR6112, Université de Nantes, 44322 Nantes, France
Copyright Elsevier
*Find the extensive, full author and affiliation list on the publishers website

The Curiosity rover’s campaign at Pahrump Hills provides the first analyses of lower Mount Sharp strata. Here we report ChemCam elemental composition of a diverse assemblage of post-depositional features embedded in, or cross-cutting, the host rock. ChemCam results demonstrate their compositional diversity, especially compared to the surrounding host rock: (i) Dendritic aggregates and relief enhanced features, characterized by a magnesium enhancement and sulfur detection, and interpreted as Mg-sulfates; (ii) A localized observation that displays iron enrichment associated with sulfur, interpreted as Fe-sulfate; (iii) Dark raised ridges with varying Mg- and Ca-enriched compositions compared to host rock; (iv) Several dark-toned veins with calcium enhancement associated with fluorine detection, interpreted as fluorite veins. (v) Light-toned veins with enhanced calcium associated with sulfur detection, and interpreted as Ca-sulfates. The diversity of the Pahrump Hills diagenetic assemblage suggests a complex post-depositional history for fine-grained sediments for which the origin has been interpreted as fluvial and lacustrine. Assessment of the spatial and relative temporal distribution of these features shows that the Mg-sulfate features are predominant in the lower part of the section, suggesting local modification of the sediments by early diagenetic fluids. In contrast, light-toned Ca-sulfate veins occur in the whole section and cross-cut all other features. A relatively late stage shift in geochemical conditions could explain this observation. The Pahrump Hills diagenetic features have no equivalent compared to targets analyzed in other locations at Gale crater. Only the light-toned Ca-sulfate veins are present elsewhere, along Curiosity’s path, suggesting they formed through a common late-stage process that occurred at over a broad area.

¹A. Bouvier, ²M. Boyet
Nature 537, 399–402   Link to Article  [doi:10.1038/nature19351]
¹University of Western Ontario, Department of Earth Sciences, Centre for Planetary Science and Exploration, London, Ontario N6A 3K7, Canada
²Clermont Université, Université Blaise Pascal, Laboratoire Magmas et Volcans, UMR CNRS 6524, Campus Universitaire des Cézeaux, 6 avenue Blaise Pascal, 63178 Aubière Cedex, France

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^1,2C. Burkhardt, ³L. E. Borg, ^2,3G. A. Brennecka, ^2,3Q. R. Shollenberger, ¹N. Dauphas ²T. Kleine
Nature 537, 394–398 Link to Article [doi:10.1038/nature18956]
¹Origins Laboratory, Department of the Geophysical Sciences and Enrico Fermi Institute, The University of Chicago, 5734 South Ellis Avenue, Chicago, Illinois 60637, USA
²Institut für Planetologie, Westfälische Wilhelms-Universität Münster, Wilhelm Klemm-Strasse 10, 48149 Münster, Germany
³Lawrence Livermore National Laboratory, L231, Livermore, California 94550, USA

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^1,2Guénon, S., ^1,3Ramírez, J.G., ^1,4Basaran, A.C., ¹Wampler, J., ⁵Thiemens, M., ¹Schuller, I.K.
Journal of Superconductivity and Novel Magnetism (in Press) Link to Article [doi:10.1007/s10948-016-3708-7]
¹Department of Physics and Center for Advanced Nanoscience, University of California, La Jolla, San Diego, CA, United States
²CQ Center for Collective Quantum Phenomena and their Applications in LISA +, Physikalisches Institut, Eberhard Karls Universität Tübingen, Auf der Morgenstelle 14, Tübingen, Germany
³Department of Physics, Universidad de los Andes, Bogotá, Colombia
⁴Department of Physics, Gebze Technical University, Gebze, Kocaeli, Turkey
⁵Department of Chemistry and Biochemistry, University of California, La Jolla, San Diego, CA, United States

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¹C.D. Cino, ¹E. Dehouck, ¹S.M. McLennan
Icarus (in Press) Link to Article [http://dx.doi.org/10.1016/j.icarus.2016.08.029]
¹Department of Geosciences, State University of New York at Stony Brook, Stony Brook NY, 11794-2100, USA
Copyright Elsevier

Burns formation sandstones, deposited by aeolian processes and preserved at Meridiani Planum, Mars, contain abundant sulfate minerals. These sedimentary rocks are thought to be representative of a sulfate-rich geological epoch during late Noachian – early Hesperian time that followed an earlier clay-rich epoch. Twenty Burns formation targets, abraded by the Rock Abrasion Tool (RAT) and for which alpha-particle X-ray spectrometry (APXS) and Mössbauer spectroscopy data are available, were selected for geochemical modeling. A linear unmixing modeling approach was employed. Mineralogical constituents quantitatively constrained by Mössbauer and Mini-TES spectroscopy and interpreted to be chemically precipitated from aqueous fluids during deposition and/or early diagenesis were subtracted from the bulk chemistry. Resulting residual chemical compositions, interpreted to be dominated by detrital siliciclastic components and representing ∼21–35% of the rocks, were then geochemically evaluated to constrain the potential for the presence of clay minerals or their poorly-crystalline or non-crystalline precursors/chemical equivalents. Calculations incorporated a robust estimate of the uncertainties in mineral abundances. On Al2O3 – (CaO+Na2O) – K2O (A-CN-K) and Al2O3 – (CaO+Na2O+K2O) – (FeOtotal+MgO) (A-CNK-FM) molar ternary diagrams, removal of chemical constituents resulted in a shift from igneous–like compositions to compositions consistent with secondary mineral assemblages containing significant aluminous clay mineral components. All of the residual compositions are corundum-normative, further supportive of the presence of highly aluminous phases. On the A-CNK-FM diagram, clay minerals plotting closest to the residual field are natural montmorillonites but could also represent mixtures of various Mg/Fe-rich phyllosilicates, such as nontronite or saponite, and other more Al-rich minerals such as Al-montmorillonite, kaolinite or illite. Depending on the age of clay mineral formation, occurrence of clay minerals or their poorly crystalline precursors/chemical equivalents in the Burns formation could suggest that any global transition from clay-rich to sulfate-rich environments on early Mars was more complex than previously recognized. Results are also consistent with models for the Burns formation aqueous history in which acidic conditions were more restricted in time and/or space than previously thought and thus may also be consistent with growing evidence that changing redox conditions, rather than global pH variations, was an important factor in the environmental evolution of early Mars.

^1,2Joshua F. Einsle, ¹Richard J. Harrison, ³Takeshi Kasama, ⁴Pádraig Ó Conbhuí, ⁵Karl Fabian, ⁴Wyn Williams, ⁷Leonie Woodland, ⁸Roger R. Fu, ⁹Benjamin P. Weiss,²Paul A. Midgley
American Mineralogist 101,  2070-2084 Link to Article [http://dx.doi.org/10.2138/am-2016-5738CCBY]
¹Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge CB2 3EQ, U.K.
²Department of Materials Science & Metallurgy, University of Cambridge, Charles Babbage Road, Cambridge CB3 0FS, U.K.
³Center for Electron Nanoscopy, Technical University of Denmark, Kongens Lyngby, Denmark
⁴Grant Institute of Earth Science, University of Edinburgh, Kings Buildings, West Mains Road, Edinburgh EH9 3JW, U.K.
⁵Geological Survey of Norway, Leiv Eirikssons vei 39, 7491 Trondheim, Norway
⁶Centre for Arctic Gas Hydrate, Environment and Climate; Department of Geology, University of Tromsø, NO-9037 Tromsø, Norway
⁷The Stephen Perse Foundation, Union Road, Cambridge CB2 1HF, U.K.
⁸Lamont-Doherty Earth Observatory, Columbia University, Palisades, New York 10964, U.S.A.
⁹Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts
Copyright: The Mineralogical Society of America

Dusty olivine (olivine containing multiple sub-micrometer inclusions of metallic iron) in chondritic meteorites is considered an ideal carrier of paleomagnetic remanence, capable of maintaining a faithful record of pre-accretionary magnetization acquired during chondrule formation. Here we show how the magnetic architecture of a single dusty olivine grain from the Semarkona LL3.0 ordinary chondrite meteorite can be fully characterized in three dimensions, using a combination of focused ion beam nanotomography (FIB-nT), electron tomography, and finite-element micromagnetic modeling. We present a three-dimensional (3D) volume reconstruction of a dusty olivine grain, obtained by selective milling through a region of interest in a series of sequential 20 nm slices, which are then imaged using scanning electron microscopy. The data provide a quantitative description of the iron particle ensemble, including the distribution of particle sizes, shapes, interparticle spacings and orientations. Iron particles are predominantly oblate ellipsoids with average radii 242 ± 94 × 199 ± 80 × 123 ± 58 nm. Using analytical TEM we observe that the particles nucleate on sub-grain boundaries and are loosely arranged in a series of sheets parallel to (001) of the olivine host. This is in agreement with the orientation data collected using the FIB-nT and highlights how the underlying texture of the dusty olivine is crystallographically constrained by the olivine host. The shortest dimension of the particles is oriented normal to the sheets and their longest dimension is preferentially aligned within the sheets. Individual particle geometries are converted to a finite-element mesh and used to perform micromagnetic simulations. The majority of particles adopt a single vortex state, with “bulk” spins that rotate around a central vortex core. We observed no particles that are in a true single domain state. The results of the micromagnetic simulations challenge some preconceived ideas about the remanence-carrying properties of vortex states. There is often not a simple predictive relationship between the major, intermediate, and minor axes of the particles and the remanence vector imparted in different fields. Although the orientation of the vortex core is determined largely by the ellipsoidal geometry (i.e., parallel to the major axis for prolate ellipsoids and parallel to the minor axis for oblate ellipsoids), the core and remanence vectors can sometimes lie at very large (tens of degrees) angles to the principal axes. The subtle details of the morphology can control the overall remanence state, leading in some cases to a dominant contribution from the bulk spins to the net remanence, with profound implications for predicting the anisotropy of the sample. The particles have very high switching fields (several hundred millitesla), demonstrating their high stability and suitability for paleointensity studies.

¹Queenie H.S. Chan, ¹Michael E. Zolensky, ²James E. Martinez, ³Akira Tsuchiyama, ³Akira Miyake
American Mineralogist 101, 2041-2050  Link to Article [http://dx.doi.org/10.2138/am-2016-5604]
¹ARES, NASA Johnson Space Center, Houston, Texas 77058, U.S.A.
²Jacobs Engineering, Houston, Texas 77058, U.S.A.
³Graduate School of Science, Kyoto University, Kitashirakawa Oiwake-cho, Sakyo-ku, Kyoto 606-8502, Japan
Copyright: The Mineralogical Society of America

Life on Earth shows preference toward the set of organics with particular spatial configurations. Enantiomeric excesses have been observed for α-methyl amino acids in meteorites, which suggests that chiral asymmetry might have an abiotic origin. A possible abiotic mechanism that could produce chiral asymmetry in meteoritic amino acids is their formation under the influence of asymmetric catalysts, as mineral crystallization can produce spatially asymmetric structures. Although magnetite plaquettes have been proposed to be a possible candidate for an asymmetric catalyst, based on the suggestion that they have a spiral structure, a comprehensive description of their morphology and interpretation of the mechanism associated with symmetry-breaking in biomolecules remain elusive. Here we report observations of magnetite plaquettes in carbonaceous chondrites (CC) that were made with scanning electron microscopy and synchrotron X-ray computed microtomography (SXRCT). We obtained the crystal orientation of the plaquettes using electron backscatter diffraction (EBSD) analysis. SXRCT permits visualization of the internal features of the plaquettes. It provides an unambiguous conclusion that the plaquettes are devoid of a spiral feature and, rather that they are stacks of individual magnetite disks that do not join to form a continuous spiral. Despite the lack of spiral features, our EBSD data show significant changes in crystal orientation between adjacent magnetite disks. The magnetite disks are displaced in a consistent relative direction that lead to an overall crystallographic rotational mechanism. This work offers an explicit understanding of the structures of magnetite plaquettes in CC, which provides a fundamental basis for future interpretation of the proposed symmetry-breaking mechanism.

^1,2A.P. Jordan, ^2,3T.J. Stubbs, ^1,2J.K. Wilson, ^1,2N.A. Schwadron, ^1,2H.E. Spence
Icarus (in Press) Link to Article [http://dx.doi.org/10.1016/j.icarus.2016.08.027]
¹Institute for the Study of Earth, Oceans, and Space, University of New Hampshire, Durham, New Hampshire, USA
²Solar System Exploration Research Virtual Institute, NASA Ames Research Center, Moffett Field, California, USA
³NASA Goddard Space Flight Center, Greenbelt, Maryland, USA
Copyright Elsevier

Large solar energetic particle events may cause dielectric breakdown in the upper 1 mm of regolith in permanently shadowed regions (PSRs). We estimate how the resulting breakdown weathering compares to meteoroid impact weathering. Although the SEP event rates measured by the Cosmic Ray Telescope for the Effects of Radiation (CRaTER) on the Lunar Reconnaissance Orbiter (LRO) are too low for breakdown to have significantly affected the regolith over the duration of the LRO mission, regolith gardened by meteoroid impacts has been exposed to SEPs for ∼106 yr. Therefore, we estimate that breakdown weathering’s production rate of vapor and melt in the coldest PSRs is up to 1.8−3.5×10−71.8−3.5×10−7 kg m−2−2 yr−1,−1, which is comparable to that produced by meteoroid impacts. Thus, in PSRs, up to 10–25% of the regolith may have been melted or vaporized by dielectric breakdown. Breakdown weathering could also be consistent with observations of the increased porosity (“fairy castles”) of PSR regolith. We also show that it is conceivable that breakdown-weathered material is present in Apollo soil samples. Consequently, breakdown weathering could be an important process within PSRs, and it warrants further investigation.

^1,2Rebecca N. Greenberger, ¹John F. Mustard, ^3,4,5Gordon R. Osinski, ^3,4,6Livio L. Tornabene, ^3,4,7Alexandra J. Pontefract, ^3,4Cassandra L. Marion, ^3,4Roberta L. Flemming, ⁸Janette H. Wilson, ⁹Edward A. Cloutis
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12716]
¹Department of Earth, Environmental, and Planetary Sciences, Brown University, Providence, Rhode Island, USA
²Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USA
³Centre for Planetary Science and Exploration, University of Western Ontario, London, Ontario, Canada
⁴Department of Earth Sciences, University of Western Ontario, London, Ontario, Canada
⁵Department of Physics and Astronomy, University of Western Ontario, London, Ontario, Canada
⁶SETI Institute, Mountain View, California, USA
⁷Planetary Science Institute, Tucson, Arizona, USA
⁸Headwall Photonics, Inc., Fitchburg, Massachusetts, USA
⁹Department of Geography, University of Winnipeg, Winnipeg, Manitoba, Canada
Published by arrangement with John Wiley & Sons

Meteorite impacts on Earth and Mars can generate hydrothermal systems that alter the primary mineralogies of rocks and provide suitable environments for microbial colonization. We investigate a calcite–marcasite-bearing vug at the ~23 km diameter Haughton impact structure, Devon Island, Nunavut, Canada, using imaging spectroscopy of the outcrop in the field (0.65–1.1 μm) and samples in the laboratory (0.4–2.5 μm), point spectroscopy (0.35–2.5 μm), major element chemistry, and X-ray diffraction analyses. The mineral assemblages mapped at the outcrop include marcasite; marcasite with minor gypsum and jarosite; fibroferrite and copiapite with minor gypsum and melanterite; gypsum, Fe3+ oxides, and jarosite; and calcite, gypsum, clay, microcline, and quartz. Hyperspectral mapping of alteration phases shows spatial patterns that illuminate changes in alteration conditions and formation of specific mineral phases. Marcasite formed from the postimpact hydrothermal system under reducing conditions, while subsequent weathering oxidized the marcasite at low temperatures and water/rock ratios. The acidic fluids resulting from the oxidation collected on flat-lying portions of the outcrop, precipitating fibroferrite + copiapite. That assemblage then likely dissolved, and the changing chemistry and pH resulting from interaction with the calcite-rich host rock formed gypsum-bearing red coatings. These results have implications for understanding water–rock interactions and habitabilities at this site and on Mars.