¹Thomas Kenkmann, ²Kent A. Sundell, ³Douglas Cook
Scientific Reports 8, 13246 Link to Article [https://doi.org/10.1038/s41598-018-31655-4]
¹Institut für Geo- und Umweltnaturwissenschaften, Albert-Ludwigs-Universität Freiburg, Baden-Württemberg, Germany
²Casper College, Casper, WY, USA
³Independent Consultant, Colorado Springs, CO, USA

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Mario Fischer-Gödde^1,2, Daniel Schwander³, and Ulrich Ott^4,5
The Astronomical Journal 156, 176 Link to Article [https://doi.org/10.3847/1538-3881/aadf33]
¹Institut für Geologie und Mineralogie, Universität zu Köln, Zülpicher Str. 49b, D-50674 Köln, Germany
²Institut für Planetologie, Westfälische Wilhelms-Universität Münster, Wilhelm-Klemm-Str. 10, D-48149 Münster, Germany
³Steinmann-Institut, Rheinische Friedrich-Wilhelms-Universität, Meckenheimer Allee 169, D-53115 Bonn, Germany
⁴MTA Atomki, Bem tér 18/c, HU-4026 Debrecen, Hungary
⁵Max-Planck-Institut für Chemie, Hahn-Meitner-Weg 1, D-55128 Mainz, Germany

Refractory metal nuggets (RMNs) are among the first solids formed in the nascent solar system. They contain high abundances of refractory metals like Re, Os, W, Ir, Ru, and Pt. The isotopic compositions of these elements bear testimony to the stellar sources that contributed to the nucleosynthetic makeup of our solar system. We report the first high-precision Ru isotope data for a bulk RMN sample prepared from the Allende meteorite. The RMNs display well-resolved mass-independent anomalies with positive anomalies for ⁹⁶Ru, ⁹⁸Ru, ¹⁰⁰Ru, ¹⁰²Ru, and ¹⁰⁴Ru. These are best explained by a deficit in r-process combined with a slight deficit in p-process nuclides. This finding stands in stark contrast to the s-process deficit isotopic patterns observed for Allende Ca–Al-rich inclusions (CAIs), bulk Allende, and other bulk meteorites. The contrasting r-, p-deficit versus s-deficit Ru isotopic signatures observed between RMNs and CAIs is surprising, given that CAIs are assumed to be a major host phase of RMNs. One way to explain the s-deficit patterns observed for CAIs and bulk meteorites is that r– and p-process Ru nuclides were added to the solar nebula after RMN formation and prior to the formation of CAIs and the accretion of meteorite parent bodies. A possible source may have been a nearby core-collapse supernova that injected freshly synthesized r– and p-process nuclides into the nascent solar system. The injection of such r– and p-enriched matter represents an alternative mechanism to account for the s-process variability presented by CAIs and bulk carbonaceous meteorites.

¹Michael P. Lucas, ¹Joshua P. Emery, ²Takahiro Hiroi, ¹Harry Y. McSween
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13203]
¹Department of Earth & Planetary Sciences, University of Tennessee, Knoxville, Tennessee, USA
²Department of Earth, Environmental and Planetary Sciences, Brown University, Providence, Rhode Island, USA
Published by arrangement with John Wiley & Sons

Except for asteroid sample return missions, measurements of the spectral properties of both meteorites and asteroids offer the best possibility of linking meteorite groups with their parent asteroid(s). Visible plus near‐infrared spectra reveal distinguishing absorption features controlled mainly by the Fe²⁺ contents and modal abundances of olivine and pyroxene. Meteorite samples provide relationships between spectra and mineralogy. These relationships are useful for estimating the olivine and pyroxene mineralogy of stony (S‐type) asteroid surfaces. Using a suite of 10 samples of the acapulcoite–lodranite clan (ALC), we have developed new correlations between spectral parameters and mafic mineral compositions for partially melted asteroids. A well‐defined relationship exists between Band II center and ferrosilite (Fs) content of orthopyroxene. Furthermore, because Fs in orthopyroxene and fayalite (Fa) content in olivine are well correlated in these meteorites, the derived Fs content can be used to estimate Fa of the coexisting olivine. We derive new equations for determining the mafic silicate compositions of partially melted S‐type asteroid parent bodies. Stony meteorite spectra have previously been used to delineate meteorite analog spectral zones in Band I versus band area ratio (BAR) parameter space for the establishment of asteroid–meteorite connections with S‐type asteroids. However, the spectral parameters of the partially melted ALC overlap with those of ordinary (H) chondrites in this parameter space. We find that Band I versus Band II center parameter space reveals a clear distinction between the ALC and the H chondrites. This work allows the distinction of S‐type asteroids as nebular (ordinary chondrites) or geologically processed (primitive achondrites).

^1,2Matthew R.M.Izawa, Edward A.Cloutis, ¹Tesia Rhind, ³Stanley A.Mertzman, ¹Daniel M.Applin, ⁴Jessica M.Stromberg, ⁵David M.Sherman
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2018.10.002]
¹Department of Geography, Univeristy of Winnipeg, Winnipeg MB R3B 2E9 Canada
²Institute for Planetary Materials, Okayama University – Misasa, 827 Yamada, Misasa, Tottori 682-0193, Japan
³Department of Earth and Environment, Franklin and Marshall College, Lancaster, Pennsylvania, USA 17604-2615
⁴CSIRO Mineral Resources Flagship, 26 Dick Perry Avenue, WA 6151, Australia
⁵School of Earth Sciences, University of Bristol, Bristol BS8 1RJ United Kingdom
Copyright Elsevier

Magnetite (Fe³⁺(Fe²⁺Fe³⁺)₂O₄) is ubiquitous in Earth and planetary materials, forming in igneous, metamorphic, and sedimentary settings, sometimes influenced by microbiology. Magnetite can be used to study many and varied planetary processes, such as the oxidation state of magmas, paleomagnetism, water-rock interactions such as serpentinization, alteration and metamorphism occurring on meteorite parent bodies, and for astrobiology. The spectral reflectance signature of magnetite in the ultraviolet, visible, and near-infrared is somewhat unusual compared to common planetary materials, suggesting that remote detection and characterization of magnetite should be possible. Here we present a systematic investigation of the reflectance spectral properties of magnetite using natural and synthetic samples. We investigate the effects of chemical substitutions, grain size variations, and mixtures with other phases in order to better constrain remote spectral searches for, and interpretation of, magnetite-bearing lithologies. Magnetite is characterized by high extinction over the entire wavelength range considered here, and therefore surface scattering dominates over volume scattering. Magnetite reflectance spectra are strongly influenced by the presence of delocalized electrons above the Verwey transition temperature (∼120 K), leading to metal-like scattering behavior, that is, high extinction, surface scattering dominant, and a general increase in reflectance with increasing wavelength, “red-sloped and featureless”. Superimposed upon the metal-like reflectance are local reflectance maxima which we ascribe to Fresnel reflectance peaks corresponding to Fe-O oxygen-metal charge transfer processes (∼0.27 and ∼0.39 μm) and Fe-related field-d orbital transitions (∼0.65 μm). We also find a systematic shift in the wavelength position of the 0.65 μm Fresnel peak with increasing chemical impurity in magnetite. Magnetite reflectance spectra are most similar to those of titanomagnetite and wüstite, and unlike those of other Fe-(Ti) oxides, such as ilmenite, hæmatite, ulvospinel, maghemite, pseudobrookite, and armalcolite.

¹Bruce Hapke, ²Hiroyuki Sato, ³Mark Robinson
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2018.10.001]
¹Department of Geology and Environmental Science, University of Pittsburgh, Pittsburgh. PA 15260.
²Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, 3-1-1 Yoshinodal, Chuo-Ku, Sagamihara, Kanagawa, 252-5210, JAPAN.
³School of Earth and Space Exploration, Arizona State University, Tempe, AZ 85287.
Copyright Elsevier

A new algorithm is proposed for estimating TiO2 abundance on the moon using lunar reflectance values measured by the Wide Angle Camera on the Lunar Reconnaissance Orbiter spacecraft. The algorithm provides useful values for mature regoliths on the entire lunar surface including highlands and low titanium maria. However, it underestimates the abundances of immature regoliths, so that the algorithm returns a lower limit for such features as young craters and rays.

¹Rebecca J. Smith, ²Elizabeth B. Rampe, ¹Briony H. N. Horgan, ³Erwin Dehouck
Journal of Geophysical Research, Planets (in Press) Link to Article [https://doi.org/10.1029/2018JE005612]
¹Department of Earth, Atmospheric, and Planetary Sciences, Purdue University, West Lafayette, IN
²NASA/Johnson Space Center, Houston, TX
³Laboratoire de Géologie de Lyon – Terre, Planètes, Environnement, UMR 5276, CNRS, Université Lyon 1, ENS Lyon, Villeurbanne, France
Published by arrangement with John Wiley & Sons

X‐ray amorphous materials have been detected in all samples measured by the CheMin X‐ray diffractometer (XRD) onboard the Mars Science Laboratory rover in Gale Crater, Mars. The origin (s) of these materials are poorly understood, and there are significant uncertainties on their estimated abundances and compositions. Three methods are used to estimate the bulk amorphous component abundance and composition of martian samples using XRD and bulk chemical data: (1) Rietveld refinements, (2) FULLPAT analyses, and (3) mass balance calculations (MBCs). We tested these methods against a quantitative XRD (internal standard) method commonly used in terrestrial laboratories. Additionally, we tested for instrumentation effects by measuring our samples on a laboratory XRD instrument (PANalytical X’Pert Pro) and the CheMin test‐bed instrument (CheMin IV). We used three natural samples known to contain amorphous materials: glacial sediment, Hawaiian soil, and a paleosol. Our methods resulted in nine amorphous abundances and four amorphous compositions for each sample. For a single sample, amorphous abundance estimates and amorphous compositions are relatively similar across all estimation methods. CheMin analog measurements perform well in our tests, with amorphous abundances and compositions comparable to laboratory QXRD measurements, though slightly underestimated. This suggests that previous amorphous component estimates for martian samples are relatively accurate. This study highlights the usefulness of the MBC method for characterizing amorphous materials in terrestrial samples, providing important supplemental information to destructive and time‐consuming size‐separation and dissolution procedures.

^1,2K. Fiege, ²M. Guglielmino, ³N. Altobelli, ²M. Trieloff, ⁴R. Srama, ¹T. M. Orlando
Journal of Geophysical Research, Planets (in Press) Link to Article [https://doi.org/10.1029/2018JE005564]
¹Georgia Institute of Technology, Atlanta, GA, USA
²Universität Heidelberg, Klaus–Tschira–Labor für Kosmochemie, Institut für Geowissenschaften, Heidelberg, Germany
³ESA, European Space Agency, Madrid, Spain
⁴Institut für Raumfahrtsysteme, Universität Stuttgart, Stuttgart, Germany
Published by arrangement with John Wiley & Sons

The role of micrometeorite bombardment in space weathering on asteroid surfaces was studied using a 2 MV Van–De–Graaff accelerator. About 90000–100000 micron– to sub–micron sized copper particles with a mass– and velocity distribution similar to the interplanetary dust population, were fired onto the surfaces of polished Allende CV3 chondrite and eucrite NWA 6966 samples at speeds between km s−1. We find a clear relationship between micro–particle bombardment, infrared reflectance decrease, and overall spectral reddening. Differences in impact effects due to variable particle speed, size and structure are observed. Some Cu–particles form large clusters that break up upon impact and disperse. Other impactors leave imprints on the surface, implant or generate typical craters with rims and spallation features. Very small, fast particles generate small craters without spallation or significant crater rim. Mid–IR–spectra (bulk– and microscopic measurements of individual components), 3D–Laser microscopic images and XRD–spectra from the processed and unprocessed samples were collected. Mid–IR–spectra (700–6000 cm−1) over the entire sample surface, show overall darkening of features. Microscopic IR–spectra show the damage seen as reflectance decrease and spectral reddening, which is variable in the μ–range, depending on impact density and target properties (mineralogic composition). The fine–grained Allende matrix with predominantly Fe–rich olivine seems less affected than coarse–grained chondrules with Mg–rich silicates, where darkening can reach 60%. XRD–analysis also suggests chemical and crystallographical differences in the bombarded sample, due to impact shock.

¹Nicolas Altobelli, ^2,3Katherina Fiege, ⁴Benoit Carry, ³Rachel Soja, ²Massimo Guglielmino, ²Mario Trieloff, ⁵Thomas Michael Orlando, ²Ralf Srama
Journal of Geophysical Research, Planets (in Press) Link to Article [https://doi.org/10.1029/2018JE005563]
¹ESA, European Space Agency, Madrid, Spain
²Klaus–Tschira–Labor für Kosmochemie, Institut für Geowissenschaften, Universität Heidelberg, Germany
³Institut für Raumfahrtsysteme, Universität Stuttgart, Stuttgart, Germany
⁴Université Côte d’ Azur, Observatoire de la Côte d’Azur, CNRS, Laboratoire Lagrange, France
⁵Georgia Institute of Technology, Atlanta, GA, USA
Published by arrangement with John Wiley & Sons

The processes of alteration of airless bodies exposed to the space environment are referred to be as ‘space weathering’. Multiple agents contribute generally to space weathering, to an extent that depends on the specific location of the surface within the Solar System. Typical space weathering agents encountered in the Solar System are: solar radiation, solar wind and cosmic rays, magnetospheric plasma (for example, at Jupiter or Saturn), and cosmic dust. The effect of space weathering is generally assessed by measuring the surfaces optical properties, for example by near‐infrared (IR) spectroscopy. The alteration of the surfaces is due to a cumulative effect over time of all agents. We investigate in this paper the contribution of micro‐meteoroid (dust) bombardment on different asteroids, by using the Micrometeoroid Environment Model (IMEM) for the interplanetary dust populations (IDPs), and a simplified model of Interstellar Dust (ISD) dynamics. We quantify, for different representative asteroids (Main Belt and NEOs), the particle cumulative flux, mass flux, impact velocity and the kinetic impact energy deposited. This work is primarily intended to support laboratory work investigating the effect of energy deposition onto sample surfaces, as well as astronomical observations of optical properties of asteroid surfaces.

¹Pablo Núñez Demarcoa, ²Gonzalo Tancredi, ³Maria Elizabeth Zucolotto, ⁵Loiva Lizia Antonello, ³José María Monzón, ⁴Valentina Pezano, ⁵Amanda Tosi, ¹Caio Villaça
Planetary and Space Science (in Press) Link to Article [https://doi.org/10.1016/j.pss.2018.09.007]
¹Instituto de Ciencias Geológicas, Facultad de Ciencias, UdelaR, Uruguay
²Departamento de Astronomía, Instituto de Física, Facultad de Ciencias, UdelaR, Uruguay
³LABET/MN/UFRJ, Laboratório Extraterrestre, Departamento de Geologia e Paleontologia, Museu Nacional, Universidade Federal do Rio de Janeiro, Brazil
⁴Centro Universitario Regional Este, UdelaR, Uruguay
⁵LABSONDA/IGEO/UFRJ, Instituto de Geociências, Universidade Federal do Rio de Janeiro, Brazil

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¹David L.Cook, ²Thomas Smith, ²Ingo Leya, ³Connor D.Hilton, ³Richard J.Walker, ¹Maria Schönbächler
Earth and Planetary Science Letters 503, 29-36 Link to Article [https://doi.org/10.1016/j.epsl.2018.09.021]
¹Institut für Geochemie und Petrologie, ETH Zürich, Clausiusstrasse 25, 8092 Zürich, Switzerland
²Space Research and Planetology, University of Bern, Sidlerstrasse 5, 3012 Bern, Switzerland
³Department of Geology, University of Maryland, 8000 Regents Dr., College Park, MD 20742, USA
Copyright Elsevier

The origin of 180W excesses in iron meteorites has been a recently debated topic. Here, a suite of IIAB iron meteorites was studied in order to accurately determine the contribution from galactic cosmic rays (GCR) and from potential decay of 184Os to measured excesses in the minor isotope 180W. In addition to W isotopes, trace element concentrations (Re, Os, Ir, Pt, W) were determined on the same samples, as well as their cosmic ray exposure ages, using 36Cl–36Ar systematics. These data were used in combination with an improved model of GCR effects on W isotopes to correct effects resulting from neutron capture and spallation reactions. After these corrections, the residual 180W excesses correlate with Os/W ratios and indicate a clear contribution from 184Os decay. A newly derived decay constant is equivalent to a half-life for 184Os of (3.38 ± 2.13) × 1013 a. Furthermore, when the data are plotted on an Os–W isochron diagram, the intercept (ε180Wi = 0.63 ± 0.35) reveals that the IIAB parent body was characterized by a small initial nucleosynthetic excess in 180W upon which radiogenic and GCR effects were superimposed. This is the first cogent evidence for p-process variability in W isotopes in early Solar System material.