¹Frans J. M. Rietmeijer
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13201]
¹Earth and Planetary Sciences, University of New Mexico, Albuquerque, New Mexico, USA
Published by arrangement with John Wiley & Sons

So far there is no conclusive evidence for water in the nucleus of 81P/comet Wild 2. Recently magnetite in collected Wild 2 samples was cited as proxy evidence for parent body aqueous alteration in this comet (Hicks et al. 2017). A potentional source for water of hydration would be layer silicates but unfortunately there is no record, neither texturally nor chemically, for hydrated layer silicates that survived hypervelocity impact in the Wild 2 samples. This paper reports large vesicles in the matrix of allocation C2044,2,41,2,5 from a volatile‐rich type B/C Stardust track. These vesicles were probably caused by boiling water that were generated when hydrated Wild 2 silicates impacted the near‐surface silica aerogel layer. Potential water sources were partially and fully hydrated GEMS (glass with embedded metal and sulfides) and CI carbonaceous chondrite materials among the earliest dusts that experienced hydration and icy‐body formation and long‐range transport and mixing with materials from across the solar system.

¹Melissa K.Ward, ¹Wayne H.Pollard
Earth and Planetray Science Letters 504, 126-138 Link to Article [https://doi.org/10.1016/j.epsl.2018.10.001]
¹Department of Geography, McGill University, Montreal, Canada
Copyright Elsevier

On Axel Heiberg Island in the Canadian High Arctic, low temperature perennial saline springs occur despite thick permafrost and cold polar desert conditions marked by a mean annual air temperature close to −20 °C. We present the first comprehensive geomorphic study of the Stolz Diapir Spring (79°04′30″N; 87°04′30″W), a unique groundwater system due to its known fresh water source and sodium chloride-dominated chemistry. During winter, spring discharge precipitates hydrohalite (NaCl⋅2H2O) by freezing fractionation that forms a pool and barrage system morphologically similar to carbonate travertines and tufas found in temperate climates. The deposit is the largest hydrohalite accumulation on Earth based on published sources. This system experiences dramatic seasonal differences in hydrology and mineralogy marked by a switch from winter regime of salt deposition and cascading surface flow from pool to pool to a summer regime marked by chemical and mechanical erosion and deposit subsurface flow. The warmer temperatures also cause the decomposition of hydrohalite to halite. Accordingly, this site is a useful analogue for similar structures identified on Mars located in areas rich in evaporite minerals and lacking evidence of volcanic activity.

^1,2,3Danielle N. Simkus, ^2,4José C. Aponte, ⁵Robert W. Hilts, ²Jamie E. Elsila, ¹Christopher D. K. Herd 
Meteoritics & Planetary Science (in Press) Link to Article [https://onlinelibrary.wiley.com/doi/10.1111/maps.13202]
¹Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Alberta T6G 2R3, Canada
²Solar System Exploration Division, Code 691, NASA Goddard Space Flight Center, Greenbelt, Maryland, USA
³NASA Postdoctoral Program at NASA Goddard Space Flight Center, Greenbelt, Maryland, USA
⁴Department of Chemistry, Catholic University of America, Washington, DC, USA
⁵Department of Physical Sciences, MacEwan University, Edmonton, Alberta T6G 2R3, Canada
Published by arrangement with John Wiley & Sons

Compound‐specific carbon isotope analysis (δ¹³C) of meteoritic organic compounds can be used to elucidate the abiotic chemical reactions involved in their synthesis. The soluble organic content of the Murchison carbonaceous chondrite has been extensively investigated over the years, with a focus on the origins of amino acids and the potential role of Strecker‐cyanohydrin synthesis in the early solar system. Previous δ¹³C investigations have targeted α‐amino acid and α‐hydroxy acid Strecker products and reactant HCN; however, δ¹³C values for meteoritic aldehydes and ketones (Strecker precursors) have not yet been reported. As such, the distribution of aldehydes and ketones in the cosmos and their role in prebiotic reactions have not been fully investigated. Here, we have applied an optimized O‐(2,3,4,5,6‐pentafluorobenzyl)hydroxylamine (PFBHA) derivatization procedure to the extraction, identification, and δ¹³C analysis of carbonyl compounds in the Murchison meteorite. A suite of aldehydes and ketones, dominated by acetaldehyde, propionaldehyde, and acetone, were detected in the sample. δ¹³C values, ranging from −10.0‰ to +66.4‰, were more ¹³C‐depleted than would be expected for aldehydes and ketones derived from the interstellar medium, based on interstellar ¹²C/¹³C ratios. These relatively ¹³C‐depleted values suggest that chemical processes taking place in asteroid parent bodies (e.g., oxidation of the IOM) may provide a secondary source of aldehydes and ketones in the solar system. Comparisons between δ¹³C compositions of meteoritic aldehydes and ketones and other organic compound classes were used to evaluate potential structural relationships and associated reactions, including Strecker synthesis and alteration‐driven chemical pathways.

¹John T. Wasson
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13205]
¹Institute of Geophysics, University of California, Los Angeles, California, USA
Published by arrangement with John Wiley & Sons

A sample of Campo del Cielo with any other name would have the same composition. During the last three decades, our instrumental neutron activation analyses (INAA) of many supposedly new iron meteorites have shown an anomalously large fraction to have compositions within the compositional field of the IAB‐MG iron Campo del Cielo. A plot of Ir versus Au provides the best discrimination; only two independent‐fall irons found after 1980 with good recovery documentation fall within the 90% contour ellipse around the centroid of this Campo field, and one of these is from Antarctica. Now (early 2018) a total of 36 other irons attributed to other geographical locations have compositions that cannot be resolved from the Campo compositional field. Because it is possible that some of these are actually independent falls, the Meteoritical Society Nomenclature Committee has chosen to assign about half these meteorites Nova XXX names used for meteorites whose discovery localities are not adequately documented. However, for Campo‐like irons with too little information (e.g., total weight not known) or for which no adequately large type specimens are available, the decision is to call them Campos with the working name used during the UCLA analysis. In the UCLA Meteorite Collection, they are cataloged together with the documented Campos.

¹M. Shyam Prasad, ¹N. G. Rudraswami, ¹Agnelo Alexandre De Araujo, ¹V. D. Khedekar
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13206]
¹Geological Oceanography Division, CSIR–National Institute of Oceanography, Dona Paula, Goa, India
Published by arrangement with John Wiley & Sons

Metal in various forms is common in almost all meteorites but considerably rare among micrometeorites. We report here the discovery of two metal micrometeorites, i.e., (1) an awaruite grain similar to those found in the metal nodules of CV chondrites and (2) a metal micrometeorite of kamacite composition enclosing inclusions of chromite and merrillite. This micrometeorite appears to be a fragment of H5/L5 chondrite. These metal micrometeorites add to the inventory of solar system materials that are accreted by the Earth in microscopic form. They also strengthen the argument that a large proportion of material accreted by the Earth that survives atmospheric entry is from asteroidal sources.

¹Giulio F.D.Solferino, ²Gregor J.Golabek
Earth and Planetary Science Letters 504, 38-52 Link to Article [https://doi.org/10.1016/j.epsl.2018.09.027]
¹Department of Earth Sciences, Royal Holloway University of London, TW20 0EX Egham, United Kingdom
²Bayerisches Geoinstitut, University of Bayreuth, 95440 Bayreuth, Germany
Copyright Elsevier

The origin of pallasites has been the focus of a number of recent studies. Yet, their formation process remains elusive, while the mechanism leading to the genesis of the sub-group termed ‘mixed type’ pallasites (containing polygonal, rounded, and fragmental olivines simultaneously) is unclear. Here we test the hypothesis of mixing of olivine fragments with Fe–Ni–S after a non-destructive impact followed by annealing employing both experimental analogues and numerical models.
The experimental series evidenced that the addition of sulfur to olivine + Fe–Ni accelerates olivine grain growth, though the growth rate is reduced when Fe–Ni–S is not fully molten. This is shown to be the consequence of competing growth of olivine and Fe–Ni grains.
Numerical models satisfying available formation constraints from natural samples indicate that planetesimals with radii ≥200 km are favorable for the genesis of rounded olivine-bearing pallasites by annealing of fragments in partially molten Fe–Ni–S. Moreover, early mixing in the planetesimal can form regions containing olivine grains with different grain sizes that could explain the formation of mixed-type pallasites.

¹B. J. Tkalcec, ¹F. E. Brenker
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13204]
¹Institute of Geoscience, Goethe University, Frankfurt am Main, Germany
Published by arrangement with John Wiley & Sons

Shock is often given as the cause for many observations in meteorites due to the assumed previous exposure of most meteorites to at least one impact event that ultimately led to their ejection from their parent body. Here we present electron backscatter diffraction (EBSD) results on a substantially shocked dunitic achondrite, chassignite Northwest Africa (NWA) 8694, and question the general culpability of shock exposure for the formation of preferred orientation fabrics of meteoritic olivine crystals. Despite the ubiquitous presence of substantial shock indicators, the EBSD results for NWA 8694 reveal an absence of preferred orientation of olivine crystals, displaying instead an overall random fabric. We propose that the passage of shock waves through olivine crystals within a solid, crystalline, dunitic rock does not produce an overall preferred orientation, nor is it likely to actively form a whole‐rock random fabric but instead has likely no bearing on the formation of olivine orientation fabrics.

¹Laurette Piani, ¹Yves Marrocchi
Earth & Planetary Science Letters 504, 64-71 Link to Article [https://doi.org/10.1016/j.epsl.2018.09.031]
¹CRPG, UMR 7358 CNRS, Université de Lorraine, 54500 Vandoeuvre-lès-Nancy, France
Copyright Elsevier

Among the different groups of carbonaceous chondrites, variable concentrations of hydrous minerals and organic matter are observed that might be related to the time and/or place of formation of their asteroidal parent bodies. However, the precise distribution of these volatile-bearing components between chondrite groups and their chemical and isotopic compositions remain fairly unknown. In this study, we used a novel secondary ion mass spectrometry analytical protocol to determine the hydrogen isotopic composition of water-bearing minerals in CV-type carbonaceous chondrites. This protocol allows for the first time the D/H ratio of CV chondrite hydrous minerals to be determined without hindrance by hydrogen contributions from adjacent organic material. We found that water in the altered CV chondrites Kaba, Bali, and Grosnaja has an average D/H ratio of D/HCV-water = [144−21+8] × 10−6 (or δDCV-water = ‰−77−131+54‰, 2σ), significantly higher than water in most CM-type carbonaceous chondrites (D/HCM-water = [101 ± 6] × 10−6 or δDCM-water = −350 ± 40‰, 2σ). We show that because organic matter in CV chondrites is depleted in deuterium compared to that in CM chondrites, such differences could result from isotopic exchange between water and organics. Another possibility is that the CM and CV parent bodies sampled different reservoirs of water ice and organics characterized by variable isotopic compositions due to their different time and/or place of accretion.

^1,2Myriam Lemelin, ²Paul G.Lucey, ³Katarina Miljković, ⁴Lisa R.Gaddis, ⁴Trent Hare, ⁵Makiko Ohtake
Planetary and Space Science (in Press) Link to Article [https://doi.org/10.1016/j.pss.2018.10.003]
¹Lassonde School of Engineering, Earth and Space Science and Engineering Department, York University, 4700 Keele St, Toronto, ON, M3J 1P3, Canada
²Hawai‘i Institute of Geophysics and Planetology, Department of Geology and Geophysics, School of Ocean and Earth Science and Technology, University of Hawai‘i at Mānoa, Honolulu, HI, 96822, USA
³Department of Applied Geology, Curtin University, Perth, WA, 6845, Australia
⁴Astrogeology Science Center, United States Geological Survey, Flagstaff, AZ, 86001, USA
⁵Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, Sagamihara, Kanagawa 252-5210, Japan

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¹M.Salvatore, ²K.Truitt, ²K.Roszell, ³N.Lanza, ⁴E.Rampe, ⁵N.Mangold, ⁶E.Dehouck, ³R.Wiens, ³S.Clegg
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2018.10.007]
¹Northern Arizona University, Flagstaff, AZ
²University of Michigan-Dearborn, Dearborn, MI
³Los Alamos National Laboratory, Los Alamos, NM
⁴NASA Johnson Space Center, Houston, TX
⁵LPG-Nantes, Université de Nantes, France
⁶Université de Lyon, UCBL, ENSL, CNRS, LGL-TPE, 69622 Villeurbanne, France
Copyright Elsevier

Alteration of the uppermost surfaces of geologic materials is a pervasive process on planetary surfaces that is dependent upon factors including parent composition and the environment under which alteration is occurring. While rapid and pervasive in hot and humid climates on Earth, chemical weathering of rock surfaces has also been found to dominate in some of Earth’s coldest and driest landscapes as well. Specifically, surfaces dominated by resistant fine-grained igneous rocks in the Antarctic preserve evidence of oxidative weathering processes, which represent the initial immature surface alteration processes that stagnate due to the lack of available water and kinetics necessary for the production of more mature alteration phases. In this study, we test the hypothesis that oxidative weathering also dominates the surfaces of sedimentary rocks throughout the Antarctic. We investigated the chemistry and mineralogy of a suite of sedimentary rocks from the Transantarctic Mountains ranging from fine-grained tuffs to coarse-grained sandstones and conglomerates. Our results show that, like the previously studied fine-grained igneous rocks in the Antarctic, sedimentary rocks generally showed only minor chemical weathering signatures at their surfaces relative to their interiors. However, unlike the igneous rocks in this earlier study, the sedimentary rocks exhibited a wide variety of non-systematic differences between surface and interior compositions. This variability of surface weathering signatures is equally as complex as the physical properties and compositions inherently present within these different sedimentary lithologies. Based on these analyses, it is apparent that oxidative weathering products do not dominate the surfaces of sedimentary rocks throughout the Transantarctic Mountains, which instead exhibit a wide array of weathering signatures that are likely dependent on both lithological and environmental factors. Considering that sedimentary lithologies are widespread across a significant fraction of the martian surface, our results suggest that observed alteration signatures limited to the surfaces of martian sedimentary rocks are most likely to be minor and to vary as a result of the lithological properties of the specific rock unit and not as a result of the widespread influences of the modern cold and dry climatic conditions.