¹Andrew S. Rivkin,²Ellen S. Howell,³Joshua P. Emery
Journal of Geophysical Research, Planets (in Press) Link to Article [https://doi.org/10.1029/2018JE005833]
¹Johns Hopkins University Applied Physics Laboratory
²University of Arizona
³University of Tennessee
Published by arrangement with John Wiley & Sons

Low‐albedo, hydrated objects dominate the list of the largest asteroids. These objects have varied spectral shapes in the 3‐μm region, where diagnostic absorptions due to volatile species are found. Dawn’s visit to Ceres has extended the view shaped by ground‐based observing, and shown that world to be a complex one, potentially still experiencing geological activity.

We present 33 observations from 2.2‐4.0 μm of eight large (D > 200 km) asteroids from the C spectral complex, with spectra inconsistent with the hydrated minerals we see in meteorites. We characterize their absorption band characteristics via polynomial and Gaussian fits to test their spectral similarity to Ceres, the asteroid 24 Themis (thought to be covered in ice frost), and the asteroid 51 Nemausa (spectrally similar to the CM meteorites). We confirm most of the observations are inconsistent with what is seen in meteorites and require additional absorbers. We find clusters in band centers that correspond to Ceres‐ and Themis‐like spectra, but no hiatus in the distribution suitable for use to simply distinguish between them. We also find a range of band centers in the spectra that approaches what is seen on Comet 67P. Finally, variation is seen between observations for some objects, with the variation on 324 Bamberga consistent with hemispheric‐level difference in composition. Given the ubiquity of objects with 3‐μm spectra unlike what we see in meteorites, and the similarity of those spectra to the published spectra of Ceres and Themis, these objects appear much more to be archetypes than outliers.

^1,2Natsumi Noda,^1,2Shoko Imamura,¹Yasuhito Sekine, ²Minako Kurisu,³Keisuke Fukushi,⁴Naoki Terada,²Soichiro Uesugi,⁵Chiya Numako,²Yoshio Takahashi,⁶Jens Hartmann
Journal of Geophysical Research, Planets (in Press) Link to Article [https://doi.org/10.1029/2018JE005892]
¹Earth‐Life Science Institute, Tokyo Institute of Technology
²Department of Earth and Planetary Science, University of Tokyo
³Institute of Nature and Environmental Technology, Kanazawa University
⁴Department of Geophysics, Tohoku University
⁵Graduate School of Science, Chiba University
⁶Institute for Geology, Center for Earth System Research and Sustainability, Universität Hamburg
Published by arrangement with John Wiley & Sons

The Curiosity and Opportunity rovers have found depositions of manganese (Mn) (hydr)oxides within the veins of the sedimentary rocks at Gale and Endeavour craters. Since Mn is a redox sensitive element, revealing the chemical form of the Mn (hydr)oxide provides unique information on the redox state of the near‐surface/groundwater at the time of deposition. Here, we report results of laboratory experiments that investigated scavenging patterns of trace metals (zinc, nickel, and chromium) on different Mn (hydr)oxides in order to constrain the chemical form of the Mn precipitates found on Mars. Our results show manganese dioxide (MnO2) scavenges zinc and nickel effectively but not for chromium. The agreement of this scavenging pattern with the observations strongly suggests that the Mn (hydr)oxides found on Mars are highly likely to be MnO2. To form MnO2, oxidizing aqueous environments are required (e.g., Eh > 0.5 V at pH ~ 8). The candidates of the oxidant include molecular oxygen, ozone, nitrates, and perchlorate acids; all of which are considered to be produced by photochemical processes. The presence of MnO2 veins in sediments suggests that such atmospheric high‐Eh oxidants may have been supplied to the subsurface, possibly through hydrological cycles activated by transient warming.

^1,2Agata M. Krzesińska,³Richard Wirth,^3,4Monika A. Kusiak
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13296]
¹Centre for Earth Evolution and Dynamics, Department of Geosciences, University of Oslo, Oslo, Norway
²Department of Earth Sciences, Natural History Museum, Cromwell Road, SW7 5BD London, UK
³GeoForschungsZentrum Potsdam, Section 3.5 Surface Geochemistry, D‐14473 Potsdam, Germany
⁴Institute of Geological Sciences Polish Academy of Sciences, ING PAN, Twarda 51/55, PL‐00818 Warszawa, Poland
Published by arrangement with John Wiley & Sons

Zakłodzie is an enstatite meteorite of unknown petrogenesis. Chemically, it resembles enstatite chondrites, but displays an achondrite‐like texture. Here we report on fabric and texture analyses of Zakłodzie utilizing X‐ray computed tomography and scanning electron microscopy and combine it with a nanostructural study of striated pyroxene by transmission electron microscopy. With this approach we identify mechanisms that led to formation of the texture and address the petrogenesis of the rock. Zakłodzie experienced a shock event in its early evolution while located at some depth inside a warm parent body. Shock‐related strain inverted pyroxene to the observed mixture of intercalated orthorhombic and monoclinic polymorphs. The heat that dissipated after the peak shock was added to primary, radiogenic‐derived heat and led to a prolonged thermal event. This caused local, equilibrium‐based partial melting of plagioclase and metal‐sulfide. Partial melting was followed by two‐stage cooling. The first phase of annealing (above 500 °C) allowed for crystallization of plagioclase and for textural equilibration of metal and sulfides with silicates. Below 500 °C, cooling was faster and more heterogeneous at cm scale, allowing retention of keilite and quenching of K‐rich feldspathic glass in some parts. Our study indicates that Zakłodzie is neither an impact melt rock nor a primitive achondrite, as suggested in former studies. An impact melt origin is excluded because enstatite in Zakłodzie was never completely melted and partial melting occurred during equilibrium‐based postshock conditions. Texturally, the rock represents a transition of chondrite and achondrite and was formed when early impact heat was added to internal radiogenic heat.

¹M. Szokaluk,¹R. Jagodziński,¹A. Muszyński,¹W. Szczuciński
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13290]
¹Institute of Geology, Adam Mickiewicz University in Poznań, Bogumiła Krygowskiego 12, 61‐680 Poznań, Poland
Published by arrangement with John Wiley & Sons

Confirmed small impact craters in unconsolidated deposits are rare on Earth, and only a few have been the subjects of detailed investigations. Consequently, our knowledge of indicators permitting unambiguous identification of such structures is limited. In this work, detailed geological mapping was performed in the area of the Morasko craters, of which the largest crater is of about 96 m diameter. These craters were formed in the mid‐Holocene (~5000 yr ago) in unconsolidated sediments of a glacial terminal moraine. Fragments of the impactor—an iron meteorite—have been found in the craters’ vicinity for many decades. Despite numerous studies of the meteorite, no detailed research concerning the geological structure around the craters and of the ejecta deposits has been undertaken. The new data, including evaluation of over 52 sediment cores and 260 shallow drillings, permit the identification of four main sediment types: Neogene clays, diamicton with Neogene clay clasts containing charcoal pieces, diamicton without clasts, and sand with locally preserved paleosoil and charcoal pieces. Based on sedimentological properties, the ejecta deposits are mainly identified as diamicton with Neogene clay clasts, described as lithic impact breccia, covering locally preserved pre‐impact soil. Moreover, crater sections characterized by inverse stratigraphy of sediments are identified as belonging to overturned flaps.

¹Javier Cuadros,¹Christian Mavris,²Joseph R.Michalski,³Jose Miguel Nieto,⁴Janice L.Bishop,⁵Saverio Fiore
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2019.04.027]
¹Department of Earth Sciences, Natural History Museum, Cromwell Road, London SW7 5BD, UK
²Department of Earth Sciences, Laboratory for Space Research, University of Hong Kong, Pokfulam Road, Hong Kong, China
³Department of Earth Sciences, University of Huelva, 21071 Huelva, Spain
⁴SETI Institute, Mountain View, CA 94043, USA
⁵Institute of Methodologies for Environmental Analysis, CNR, Department of Geoenvironmental and Earth Sciences, University of Bari, Via Orabona 4, 70125 Bari, Italy
Copyright Elsevier

Investigation of Earth analogs and their environments is crucial for the full interpretation of geologic outcrops and processes on Mars. Phyllosilicates are important indicators of aqueous processes and their characterization is a significant piece of the geologic puzzle of Mars. They are chiefly investigated with Near-Infrared (NIR) spectroscopy from orbit. While these studies have revolutionized our understanding of aqueous processes on Mars, they are challenged by the chemical and structural complexity of phyllosilicates, non-linear response to mineral abundance, low penetration of infrared radiation in the target rocks, and spectral modifications caused by rock texture. Phyllosilicate-bearing samples from four locations in the Iberian Pyrite Belt (El Villar, Calañas, Quebrantahuesos, and Tharsis) were investigated using NIR, XRD and thermogravimetry in order to document the effects of acidic alteration under multiple environments and inform orbital detections on Mars. The samples are comprised of chlorite, illite, kaolinite, alunite, jarosite, goethite and interstratified chlorite-vermiculite and kaolinite-smectite. Kaolinite dominates the spectral signature relative to other phyllosilicates from abundances as low as 7 wt%. Only alunite and jarosite display spectral intensities similar to kaolinite. NIR spectra of bulk rock and <2 μm size fractions are very similar, indicating that spectra are dominated by the smaller particles. The octahedral Al-Fe-Mg composition of illite and kaolinite determine the positions of their OH combination band (~2.21 μm), commonly used for phyllosilicate characterization. The range of wavelength variation is narrower for kaolinite-dominated spectra, 2.205–2.216 μm, but wider than the spectral resolution of the orbital probe CRISM (~0.007 μm). Thus, in favorable conditions CRISM spectra can identify variations of kaolinite octahedral composition, a valuable tool to investigate kaolinite origin. A survey of kaolinite-bearing spectra from Mars (Leighton Crater, Mawrth Vallis and Nili Fossae regions) showed that most OH combination bands are within 2.205–2.212 μm. One spectrum displayed this band at 2.215–2.219 μm, and is a good candidate for kaolinite with significant Fe/Mg-substitution.

^1,2Philip R. Heck et al. (>10)
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13291]
¹Robert A. Pritzker Center for Meteoritics and Polar Studies, Field Museum of Natural History, 1400 S Lake Shore Dr, Chicago, Illinois, 60605 USA
²Chicago Center for Cosmochemistry & Department of the Geophysical Sciences, University of Chicago, Chicago, Illinois, USA
Published by arrangement with John Wiley & Sons

This document contains suggestions for best practices by authors who refer to meteorites in publications. It can also be taken as a guide for publishers in establishing guidelines for authors. The following best practices are recommended in addition to acknowledging the loaning institution or loaning individual (unless required otherwise). The main motivations are to: help ensure that research on meteorites is reproducible, prevent confusion in the literature, and enhance tracking of specimens and related data.

^1,2M. Benna,³D. M. Hurley,¹T. J. Stubbs,¹P. R. Mahaffy,⁴R. C. Elphic
Nature Geoscience  (in Press) Link to Article [https://doi.org/10.1038/s41561-019-0345-3]
¹NASA Goddard Space Flight Center, Greenbelt, MD, USA
²CSST, University of Maryland, Baltimore County, Baltimore, MD, USA
³The Johns Hopkins University Applied Physics Laboratory, Laurel, MD, USA
⁴NASA Ames Research Center, Moffett Field, CA, USA

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^1,2Jörg Fritz,^3,4Vera Assis Fernandes,³Ansgar Greshake,⁵Andreas Holzwarth,⁶Ute Böttger
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13289]
¹Saalbau Weltraum Projekt, Liebigstraße 6, 64646 Heppenheim, Germany
²Zentrum für Rieskrater und Impaktforschung Nördlingen (ZERIN), Vordere Gerbergasse 3, 86720 Nördlingen, Germany
³Museum für Naturkunde, Leibniz Institut für Biodiversität und Evolutionsforschung, Invalidenstraße 43, 10115 Berlin, Germany
⁴School of Earth and Environmental Science, University of Manchester, Oxford Road, Manchester, M13 9PL UK
⁵Ernst Mach Institut für Kurzzeitdynamik, Fraunhofer Institut, Am Klingenberg 1, 79588 Efringen‐Kirchen, Germany
⁶Institut für Optische Sensoren Systeme, Deutsches Zentrum für Luft und Raumfahrt (DLR), Rutherfordstr. 2, 12489 Berlin, Germany
Published by arrangement with John Wiley & Sons

This contribution addresses the role of chemical composition, pressure, temperature, and time during the shock transformation of plagioclase into diaplectic glass—i.e., maskelynite. Plagioclase of An_50‐57 and An₉₄ was recovered as almost fully isotropic maskelynite from room temperature shock experiments at 28 and 24 GPa. The refractive index (RI) decreased to values of a quenched mineral glass for An_50‐57 plagioclase shocked to 45 GPa and shows a maximum in An₉₄ plagioclase shocked to 41.5 GPa. The An₉₄ plagioclase experiments can serve as shock thermobarometer for lunar highland rocks and howardite, eucrite, and diogenite meteorites. Shock experiments at 28, 32, 36, and 45 GPa and initial temperatures of 77 and 293 K on plagioclase (An_50‐57) produced materials with identical optical and Raman spectroscopic properties. In the low temperature (<540 K) region, the formation of maskelynite is entirely controlled by shock pressure. The RI of maskelynite decreased in heating experiments of 5 min at temperatures of >770 K, thus, providing a conservative upper limit for the postshock temperature history of the rock. Although shock recovery experiments and static pressure experiments differ by nine orders of magnitude in typical time scale (microseconds versus hours), the amorphization of plagioclase occurs at similar pressure and temperature conditions with both methods. The experimental shock calibration of plagioclase can, together with other minerals, be used as shock thermobarometer for naturally shocked rocks.

^1,4Zalewska, N.E.,²Mroczkowska-Szerszeń, M.,³Fritz, J.,⁴, Błęcka, M.
Aircraft Engineering and Aerospace Technology 91, 333-345 Link to Article [DOI: 10.1108/AEAT-01-2018-0051]
¹Institute of Aviation, Warsaw, Poland
²Department of Geology and Geochemistry, Oil and Gas Institute, National Research Institute, Krakow, Poland
³Saalbau Weltraum Projekt, Heppenheim, Germany
⁴Department of Planetology, Space Research Center PAS, Warsaw, Poland

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^1,2Coldwell, B.C.,^1,2,3,4,5Pankhurst, M.J.
Journal of the Geological Society 176, 209-224 Link to Article [DOI: 10.1144/jgs2018-084]
¹Instituto Tecnológico y de Energías Renovables (ITER), Granadilla de Abona, Santa Cruz de Tenerife 38600, Spain
²Instituto Volcanológico de Canarias (INVOLCAN), Calle Álvaro Martín Díaz 1, San Cristóbal de La Laguna, Santa Cruz de Tenerife 38320, Spain
³School of Materials, University of Manchester, Manchester, M13 9PJ, United Kingdom
⁴Research Complex at Harwell, Harwell Campus, Didcot, OX11 0FA, United Kingdom
⁵School of Earth and Environment, University of Leeds, Leeds, LS2 9JT, United Kingdom

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