A story told by calcareous nannofossils—the timing and course of an Eocene meteorite impact in central Jordan

1Alqudah, M.,2Khoury, H., 2Salameh, E., 3Mutterlose, J.
Arabian Journal of Geosciences 11, 451 Link to Article [DOI: 10.1007/s12517-018-3776-z]
1Department of Earth and Environmental Sciences, Yarmouk University, 21163, Irbid, Jordan
2Department of Geology, University of Jordan, Amman, 11942, Jordan
3Institute for Geology, Mineralogy and Geophysics, Ruhr University Bochum, Universitätsstraße 150, Bochum, 44801, Germany

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In situ collection of dust grains falling from Saturn’s rings into its atmosphere

1Hsiang-Wen Hsu et al. (>10)
Science 362, eaat3185 Link to Article [DOI: 10.1126/science.aat3185]
1Laboratory for Atmospheric and Space Physics, University of Colorado–Boulder, Boulder, CO, USA
Reprinted with permission from AAAS

Saturn’s main rings are composed of >95% water ice, and the nature of the remaining few percent has remained unclear. The Cassini spacecraft’s traversals between Saturn and its innermost D ring allowed its cosmic dust analyzer (CDA) to collect material released from the main rings and to characterize the ring material infall into Saturn. We report the direct in situ detection of material from Saturn’s dense rings by the CDA impact mass spectrometer. Most detected grains are a few tens of nanometers in size and dynamically associated with the previously inferred “ring rain.” Silicate and water-ice grains were identified, in proportions that vary with latitude. Silicate grains constitute up to 30% of infalling grains, a higher percentage than the bulk silicate content of the rings.

Evidence for a large Paleozoic Impact Crater Strewn Field in the Rocky Mountains

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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Ruthenium Isotope Composition of Allende Refractory Metal Nuggets

Mario Fischer-Gödde1,2, Daniel Schwander3, and Ulrich Ott4,5
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.

Spectral properties and mineral compositions of acapulcoite–lodranite clan meteorites: Establishing S‐type asteroid–meteorite connections

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).


Spectral reflectance properties of magnetites: Implications for remote sensing

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.

Lunar Reconnaissance Orbiter Wide Angle Camera Algorithm for TiO2 Abundances on the Lunar Surface, including the Highlands and Low-Ti Maria

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.