¹Steven A.Binnie, ¹Kunihiko Nishiizumi, ¹Kees C.Welten, ^2,3Marc W.Caffee, ⁴Dirk Hoffmeister
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2018.09.036]
¹Space Sciences Laboratory, University of California, Berkeley, 7 Gauss Way, Berkeley, CA 94720-7450, USA
²Department of Physics and Astronomy, Purdue University, West Lafayette, IN 47907-1306, USA
³Department of Earth, Atmospheric, and Planetary Sciences, Purdue University, West Lafayette, IN 47907-1306, USA
⁴Institute for Geography, University of Cologne, Otto-Fischer-Str. 4, 50674, Cologne, Germany
Copyright Elsevier

Measurements of cosmogenic ¹⁰Be, ²⁶Al and ³⁶Cl in Apollo 16 double drive core 68002/68001 are combined with a high resolution digital surface model of the sampling site to investigate the surface processes on the Moon. We find both a significant deficit of solar cosmic ray (SCR)-produced ²⁶Al and a lack of SCR-produced ³⁶Cl in the top 3-5 g/cm² of the lunar regolith. The topographic model shows the core was taken from just inside a crater with a rim diameter of 25-30 cm. These observations are consistent with regolith removal and displacement by a shallow impact that occurred on the order of 100 kyr ago, or less. Our findings are also compatible with shallow mixing, or gardening, of the lunar regolith to depths of a few cm, a value often found in other lunar cores over the ∼10⁶ yr averaging times of ²⁶Al and ⁵³Mn measurements. More definitive regolith mixing depth estimates are not possible due to the likelihood of disturbance in the top of the core as a result of sampling and/or handling. Our results support the hypothesis that the lunar surface experiences more frequent disturbances by small primary and secondary impacts than has previously been assumed. Additionally, we find no evidence that fine-grained ejecta from the 2.0 Myr old South Ray Crater impact reached this site. If the layer of fine-grained ejecta that reached the sampling site from the South Ray Crater was no more than a few cm thick, this absence can be explained by the erosion that formed the small, relatively recent crater at the coring location.

¹Vladimir Svetsov, ¹Valery Shuvalov
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13200]
¹Institute for Dynamics of Geospheres, Russian Academy of Sciences, Moscow, Russia
Published by arrangement with John Wiley & Sons

Plumes produced by the impacts of asteroids and comets consist of rock vapor and heated air. They emit visible light, ultraviolet, and infrared radiation, which can greatly affect the environment. We have carried out numerical simulations of the impacts of stony and cometary bodies with a diameter of 0.3, 1, and 3 km, which enter the atmosphere at various angles, using a hydrodynamic model supplemented by radiation transfer. We assumed that the cosmic object has no strength, and deforms, fragments, and vaporizes in the atmosphere. After the impact on the ground, the formation of craters and plumes was simulated, taking the internal friction of destroyed rocks and the trail formed in the atmosphere into account. The equation of radiative transfer, added to the equations of gas dynamics, was used in the approximation of radiative heat conduction or, if the Rosseland optical depth of a radiating volume of gas and vapor was less than unity, in the volume‐emission approximation. We used temperature and density distributions obtained in these simulations to calculate radiation fluxes on the Earth’s surface by integrating the equation of radiative transfer along rays passing through a luminous region. We used tables of the equation of state of dunite and quartz (for stony impactors and a target) and air, as well as tables of absorption coefficients of air, vapor of ordinary chondrite, and vapor of cometary material. We have calculated the radiation impulse on the ground and the impact radiation efficiency (a ratio of thermal radiation energy incident on the ground to the kinetic energy of a body), which ranges from ~0.5% to ~9%, depending on the impactor size and the angle of entry into the atmosphere. Direct thermal radiation from fireballs and impact plumes, poses a great danger to people, animals, plants, and economic objects. After the impacts of asteroids at a speed of 20 km s−1 at an angle of 45°, a fire can occur at a distance of 250 km if the asteroid has a diameter of 0.3 km, and at a distance of 2000 km if the diameter is 3 km.

¹Hejiu Hui(惠鹤九), ²Kai-Uwe Hess, ³Youxue Zhang(张有学), ⁴Alexander R.L.Nichols, ⁵Anne H.Peslier, ³Rebecca A.Lange, ²Donald B.Dingwell, ⁶Clive R.Neal
Earth and Planetary Science Letters 503, 88-94 Link to Article [https://doi.org/10.1016/j.epsl.2018.09.019]
¹State Key Laboratory for Mineral Deposits Research & Lunar and Planetary Science Institute, School of Earth Sciences and Engineering, Nanjing University, Nanjing, Jiangsu 210023, China
²Department of Earth and Environmental Sciences, LMU-University of Munich, Theresienstrasse 41/III, 80333 Munich, Germany
³Department of Earth and Environmental Sciences, University of Michigan, Ann Arbor, MI 48109, USA
⁴Department of Geological Sciences, University of Canterbury, Christchurch 8140, New Zealand
⁵Jacobs, NASA-Johnson Space Center, Mail Code X13, Houston, TX 77058, USA
⁶Department of Civil and Environmental Engineering and Earth Sciences, University of Notre Dame, Notre Dame, IN 46556, USA
Copyright Elsevier

It is widely accepted that the Apollo 17 orange glass beads are of volcanic origin. The degree of degassing of the glass beads depends on their cooling rates, so the estimation of volatile contents in the parental magmas of these lunar pyroclastic glasses also depends on the cooling rates. The cooling rate can be estimated using the calorimetric properties of the glass across the glass transition. In this study, a series of heat capacity measurements were carried out on hand-picked lunar volcanic orange glass beads during several cycles of heating to temperatures above their glass transition using a differential scanning calorimeter. The cooling rate of orange glass beads (sample 74220,867) was calculated to be 101 K/min using the correlation between glass cooling rates and fictive temperatures estimated from their heat capacity–temperature paths. This cooling rate is close to the lower end of the range that best fits the diffusion profiles of several volatile species in the glass beads, and at the upper end of the cooling-rate range recorded in glasses quenched subaerially on Earth. The cooling rate is likely to be controlled by the cooling environment (cooling medium) such that the lunar volcanic glass beads could have been cooled in a gaseous medium released from volcanic eruptions on the Moon, but not during “free flight” in vacuum. The existence of a gas medium suggests, in turn, that there may have been at least a short-lived or episodic atmosphere on the early Moon at around 3.5 Ga.

¹Kvasnytsya, V.M.
Journal of Superhard Materials 40, 229-235 Link to Article [DOI: 10.3103/S1063457618040019]
¹Semenenko Institute of Geochemistry, Mineralogy and Ore Formation, National Academy of Sciences of Ukraine, pr. Palladina 34, Kiev 142, 03680, Ukraine

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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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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.

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.