^1,2Hitesh G. Changela,^3,4Corentin Le Guillou,⁴Sylvain Bernard,⁵Adrian J. Brearley
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.13045]
¹Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque, New Mexico, USA
²Key Laboratory for Earth & Planetary Physics, Institute of Geology & Geophysics, Chinese Academy of Sciences, Beijing, China
³Unité matériaux et Transformation (UMET), CNRS UMR 8207, Université Lille1, Villeneuve D’Ascq, France
⁴Institut de Minéralogie, de physique des matériaux et de Cosmochimie (IMPMC), Sorbonne Université, Paris 06, IRD CNRS UMR 206, Paris, France
⁵Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque, New Mexico, USA
Published by arrangement with John Wiley & Sons

The morphology, molecular composition, and distribution of organic matter (OM) were investigated in a suite of CR chondrites to better constrain its hydrothermal evolution. Multiple focused ion beam sections were extracted from the matrices of seven CR chondrites. Scanning transmission X-ray microscopy and transmission electron microscopy reveal OM ubiquitously distributed across the CR matrices. OM mainly occurs as either discrete submicron rounded or irregularly shaped vein-like particles. Two spectral populations of organic particles were identified by carbon K-edge X-ray absorption near edge structure (XANES): the most abundant one, similar to insoluble organic matter (IOM) residues, contains aromatic, carbonyl, and carboxylic groups. The second population is more aromatic-rich and lacks a distinctive carbonyl peak. An additional, ubiquitous organic component occurs associated with amorphous silicates and phyllosilicates. Less aromatic but aliphatic- and carboxylic-rich, this diffuse OM is interpreted as the result of the redistribution of organic compounds by aqueous fluids. The most altered CR1 GRO 95577 contains a more mature OM and highly aliphatic- and carboxylic-rich diffuse OM. This evolution, from the CR2s to the CR1, is comparable to that of terrestrial gas shale maturation involving cracking reactions, releasing bitumen-like, aliphatic-, and carboxylic-rich compounds, and aromatic residues. Our observations support the accretion of soluble OM and its later polymerization to IOM, as well as the maturation of IOM and its partial oxidation, releasing mobile compounds. The differences in GRO 95577 are clearly attributable to the hydrothermal episode(s), but the relative role of water and temperature on the evolution of OM remains elusive.

^1,4J.Aramendia, ^1,4L.Gomez-Nubla, ^1,4K.Castro, ^1,4S.Fdez-Ortiz de Vallejuelo, ^1,4G.Arana, ^1,4M.Maguregui, ^2,4V.G.Baonza, ^3,4J.Medina, ^3,4F.Rull, ^1,4J.M.Madariaga
TrAC Trends in Analytical Chemistry 98, 36-46 Link to Article [https://doi.org/10.1016/j.trac.2017.10.018]
¹Department of Analytical Chemistry, University of the Basque Country (UPV/EHU), P.O. Box 644, E-48080 Bilbao, Spain
²Departamento de Química Física, Facultad de Ciencias Químicas, Universidad Complutense, E-28040 Madrid, Spain
³Unidad Asociada UVA-CSIC al Centro de Astrobiología, University of Valladolid, Parque Tecnológico Boecillo, E-47151 Valladolid, Spain
⁴Spanish Science Team of the RLS Instrument, Exomars 2020 Mission of ESA to Mars, Spain

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¹Mehmet Yesiltas
Spectrochmica Acta Part A: Molecular and Biomolecular Spectroscopy 194, 92-101 Link to Article [https://doi.org/10.1016/j.saa.2018.01.021]
¹Faculty of Aeronautics and Space Sciences, Kirklareli University, Kirklareli 39000, Turkey

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^1,2Karel Lietaert, ¹Lore Thijs, ¹Bram Neirinck, ^2,3Thomas Lapauw,⁴Brian Morrison, ⁵Chris Lewicki, ¹Jonas Van Vaerenbergh
Acta Astronautica 143, 76-81 Link to Article [https://doi.org/10.1016/j.actaastro.2017.11.027]
¹3D Systems LayerWise NV, Grauwmeer 14, 3001 Leuven, Belgium
²KU Leuven Department of Materials Engineering, Kasteelpark Arenberg 44 pb2450, 3001 Leuven, Belgium
³Belgian Nuclear Research Centre SCK-CEN, Boeretang 200, 2400 Mol, Belgium
⁴ATI Powder Metals Robinson Operations, 6515 Steubenville Pike, Pittsburgh, PA 15205-1005, USA
⁵Planetary Resources, Inc., 6742 185th Ave, NE Redmond, WA 98052, USA

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^1,2Xiaojia Zeng,³Katherine H. Joy,^1,4Shijie Li,³John F. Pernet-Fisher,¹Xiongyao Li,³Dayl J. P. Martin,¹Yang Li,⁵Shijie Wang
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.13049]
¹Center for Lunar and Planetary Sciences, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang, China
²University of Chinese Academy of Sciences, Beijing, China
³School of Earth and Environmental Sciences, University of Manchester, Manchester, UK
⁴Key Laboratory of Lunar and Deep Space Exploration, National Astronomical Observatories, Chinese Academy of Sciences, Beijing, China
⁵State Key Laboratory of Environmental Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang, China
Published by arrangement with John Wiley & Sons

This study presents the petrography, mineralogy, and bulk composition of lunar regolith breccia meteorite Northwest Africa (NWA) 7948. We identify a range of lunar lithologies including basaltic clasts (very low-titanium and low-titanium basalts), feldspathic lithologies (ferroan anorthosite, magnesian-suite rock, and alkali suite), granulites, impact melt breccias (including crystalline impact melt breccias, clast-bearing impact melt breccias, and glassy melt breccias), as well as regolith components (volcanic glass and impact glass). A compositionally unusual metal-rich clast was also identified, which may represent an impact melt lithology sourced from a unique Mg-suite parent rock. NWA 7948 has a mingled bulk rock composition (Al₂O₃ = 21.6 wt% and FeO = 9.4 wt%) and relatively low concentrations of incompatible trace elements (e.g., Th = 1.07 ppm and Sm = 2.99 ppm) compared with Apollo regolith breccias. Comparing the bulk composition of the meteorite with remotely sensed geochemical data sets suggests that the sample was derived from a region of the lunar surface distal from the nearside Th-rich Procellarum KREEP Terrane. Our investigations suggest that it may have been ejected from a nearside highlands-mare boundary (e.g., around Mare Crisium or Orientale) or a cryptomare region (e.g., Schickard-Schiller or Mare smythii) or a farside highlands-mare boundary (e.g., Mare Australe, Apollo basin in the South Pole–Aitken basin). The distinctive mineralogical and geochemical features of NWA 7948 suggest that the meteorite may represent lunar material that has not been reported before, and indicate that the lunar highlands exhibit wide geological diversity.

¹G. Thangjam,¹A. Nathues,¹T. Platz,¹M. Hoffmann,²E. A. Cloutis,³K. Mengel,⁴M. R. M. Izawa,²D. M. Applin
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.13044]
¹Max Planck Institute for Solar System Research, Goettingen, Germany
²University of Winnipeg, Winnipeg, Manitoba, Canada
³IELF, TU Clausthal, Clausthal-Zellerfeld, Germany
⁴Institute for Planetary Materials, Okayama University, Misasa, Misasa, Tottori, Japan
Published by arrangement with john Wiley & Sons

Variations and spatial distributions of bright and dark material on dwarf planet Ceres play a key role in understanding the processes that have led to its present surface composition. We define limits for “bright” and “dark” material in order to distinguish them consistently, based on the reflectance of the average surface using Dawn Framing Camera data. A systematic classification of four types of bright material is presented based on their spectral properties, composition, spatial distribution, and association with specific geomorphological features. We found obvious correlations of reflectance with spectral shape (slopes) and age; however, this is not unique throughout the bright spots. Although impact features show generally more extreme reflectance variations, several areas can only be understood in terms of inhomogeneous distribution of composition as inferred from Dawn Visible and Infrared Spectrometer data. Additional material with anomalous composition and spectral properties are rare. The identification of the composition and origin of the dark, particularly the darkest material, remains to be explored. The spectral properties and the morphology of the dark sites suggest an endogenic origin, but it is not clear whether they are more or less primitive surficial exposures or excavated subsurface but localized material. The reflectance, spectral properties, inferred composition, and geologic context collectively suggest that the bright and dark material tends to gradually change toward the average surface over time. This could be because of multiple processes, i.e., impact gardening/space weathering, and lateral mixing, including thermal and aqueous alteration, accompanied by changes in composition and physical properties such as grain size, surface temperature, and porosity (compaction).

¹Ming-Chang Liu, ¹Kevin D. McKeegan, ¹T. Mark Harrison, ¹George Jarzebinski, ¹Lvcian Vltava
International Journal of Mass Spectrometry 424, 1-9 Link to Article [https://doi.org/10.1016/j.ijms.2017.11.007]
¹Department of Earth, Planetary, and Space Sciences, UCLA, United States

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¹K.D.Burgess, ¹R.M.Stroud
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2017.12.023]
¹U.S. Naval Research Laboratory, 4555 Overlook Ave. SW, Washington, DC 20375, United states
Copyright Elsevier

The solar wind is an important driver of space weathering on airless bodies. Over time, solar wind exposure alters the physical, chemical, and optical properties of exposed materials and can also impart a significant amount of helium into the surfaces of these bodies. However, common materials on the surface of the Moon, such as glass, crystalline silicates, and oxides, have highly variable responses to solar wind irradiation. We used scanning transmission electron microscopy (STEM) with electron energy loss spectroscopy (EELS) to examine the morphology and chemistry of a single grain of lunar soil that includes silicate glass, chromite and ilmenite, all present and exposed along the same surface. The exposure of the silicate glass and oxides to the same space weathering conditions allows for direct comparisons of the responses of natural materials to the complex lunar surface environment. The silicate glass shows minimal effects of solar wind irradiation, whereas both the chromite and ilmenite exhibit defect-rich rims that currently contain trapped helium. Only the weathered rim in ilmenite is rich in nanophase metallic iron (npFe0) and larger vesicles that retain helium at a range of internal pressures. The multiple exposed surfaces of the single grain of ilmenite demonstrate strong crystallographic controls of planar defects and non-spherical npFe0. The direct spectroscopic identification of helium in the vesicles and planar defects in the oxides provides additional evidence of the central role of solar wind irradiation in the formation of some common space weathering features.

¹Jérôme Aléon
Earth and Planetary Sciences 482, 324-333 Link to Article [https://doi.org/10.1016/j.epsl.2017.11.027]
¹Institut de Minéralogie, de Physique des Matériaux et de Cosmochimie UMR 7590, Sorbonne Universités, Museum National d’Histoire Naturelle, CNRS, UPMC, IRD, 61 rue Buffon, 75005 Paris, France
Copyright Elsevier

In several Calcium–Aluminum-rich Inclusions (CAIs) from the CV3 chondrites Allende and Efremovka, representative of the most common igneous CAI types (type A, type B and Fractionated with Unknown Nuclear isotopic anomalies, FUN), the relationship between 16O-excesses and TiO2 content in pyroxene indicates that the latter commonly begins to crystallize with a near-terrestrial 16O-poor composition and becomes 16O-enriched during crystallization, reaching a near-solar composition. Mass balance calculations were performed to investigate the contribution of spinel to this 16O-enrichment. It is found that a back-reaction of early-crystallized 16O-rich spinel with a silicate partial melt having undergone a 16O-depletion is consistent with the O isotopic evolution of CAI minerals during magmatic crystallization. Dissolution of spinel explains the O isotopic composition (16O-excess and extent of mass fractionation) of pyroxene as well as that of primary anorthite/dmisteinbergite and possibly that of the last melilite crystallizing immediately before pyroxene. It requires that igneous CAIs behaved as closed-systems relative to oxygen from nebular gas during a significant fraction of their cooling history, contrary to the common assumption that CAI partial melts constantly equilibrated with gas. The mineralogical control on O isotopes in igneous CAIs is thus simply explained by a single 16O-depletion during magmatic crystallization. This 16O-depletion occurred in an early stage of the thermal history, after the crystallization of spinel, i.e. in the temperature range for melilite crystallization/partial melting and did not require multiple, complex or late isotope exchange. More experimental work is however required to deduce the protoplanetary disk conditions associated with this 16O-depletion.

Moe Matsuoka et al. (>10)*
Earth, Planets and Space 69, 120 Link to Article [https://doi.org/10.1186/s40623-017-0705-4]
¹Tohoku University, Sendai, Japan

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