¹U. Raut,¹P. L. Karnes,^1,2K. D. Retherford,¹M. W. Davis,³Y. Liu,^1,2G. R. Gladstone,¹E. L. Patrick,¹Thomas K. Greathouse,⁴A. R. Hendrix,¹P. Mokashi
Journal of Geophysical Research, Planets (In Press) Link to Article [https://doi.org/10.1029/2018JE005567]
¹Space Science and Engineering Division, Southwest Research Institute, San Antonio, TX, USA
²Department of Physics and Astronomy, The University of Texas at San Antonio, San Antonio, TX, USA
³Lunar and Planetary Institute, Houston, TX, USA
⁴Planetary Science Institute, Tucson, AZ, USA
Published by arrangement with John Wiley & Sons

We report new measurements of the far‐ultraviolet (FUV) bidirectional reflectance of Apollo soil 10084 from the Southwest Research Institute ultraviolet reflectance chamber. The bidirectional reflectance distribution function of this mare soil, enriched in Ti and Fe content, is rather featureless in the FUV wavelength region of 115–180 nm, except for a small blue slope, which is attributed to the effects of space weathering. This soil preferentially backscatters FUV photons as indicated by the angular distribution of the bidirectional reflectance. The phase curves are fitted with a simplified Hapke photometric model to derive the average volume single scattering albedo and scattering phase function of the mare lunar grains. The albedo values and the backscattering nature reported here are consistent with Lunar Reconnaissance Orbiter’s Lyman‐Alpha Mapping Project ultraviolet imaging spectrograph observations, despite expected morphological differences.

¹Jason C. Cook et al. (>10)
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2018.05.024]
¹Pinhead Institute, Telluride, CO, USA
Copyright Elsevier

On July 14, 2015, NASA’s New Horizons spacecraft encountered the Pluto-system. Using the near-infrared spectral imager, New Horizons obtained the first spectra of Nix, Hydra, and Kerberos and detected the 1.5 and 2.0 μm bands of H2O-ice on all three satellites. On Nix and Hydra, New Horizons also detected bands at 1.65 and 2.21 μm that indicate crystalline H2O-ice and an ammoniated species, respectively. A similar band linked to NH3-hydrate has been detected on Charon previously. However, we do not detect the 1.99 μm band of NH3-hydrate. We consider NH4Cl (ammonium chloride), NH4NO3 (ammonium nitrate) and (NH4)2CO3 (ammonium carbonate) as potential candidates, but lack sufficient laboratory measurements of these and other ammoniated species to make a definitive conclusion. We use the observations of Nix and Hydra to estimate the surface temperature and crystalline H2O-ice fraction. We find surface temperatures  < 20 K ( < 70 K with 1-σ error) and 23 K ( < 150 K with 1-σ error) for Nix and Hydra, respectively. We find crystalline H2O-ice fractions of 78−22+12% and  > 30% for Nix an Hydra, respectively. New Horizons observed Nix and Hydra twice, about 2-3 hours apart, or 5 and 25% of their respective rotation periods. We find no evidence for rotational differences in the disk-averaged spectra between the two observations of Nix or Hydra. We perform a pixel-by-pixel analysis of Nix’s disk-resolved spectra and find that the surface is consistent with a uniform crystalline H2O-ice fraction, and a  ∼ 50% variation in the normalized band area of the 2.21 μm band with a minimum associated with the red blotch seen in color images of Nix. Finally, we find evidence for bands on Nix and Hydra at 2.42 and possibly 2.45 μm, which we cannot identify, and, if real, do not appear to be associated with the ammoniated species. We do not detect other ices, such as CO2, CH3OH and HCN.

¹G.L.Christenson et al. (>10)
Earth and Planetary Science Letters 495, 1-11 Link to Article [https://doi.org/10.1016/j.epsl.2018.05.013]
¹University of Texas Institute for Geophysics, Jackson School of Geosciences, Austin, USA
Copyright Elsevier

Joint International Ocean Discovery Program and International Continental Scientific Drilling Program Expedition 364 drilled into the peak ring of the Chicxulub impact crater. We present P-wave velocity, density, and porosity measurements from Hole M0077A that reveal unusual physical properties of the peak-ring rocks. Across the boundary between post-impact sedimentary rock and suevite (impact melt-bearing breccia) we measure a sharp decrease in velocity and density, and an increase in porosity. Velocity, density, and porosity values for the suevite are 2900–3700 m/s, 2.06–2.37 g/cm3, and 20–35%, respectively. The thin (25 m) impact melt rock unit below the suevite has velocity measurements of 3650–4350 m/s, density measurements of 2.26–2.37 g/cm3, and porosity measurements of 19–22%. We associate the low velocity, low density, and high porosity of suevite and impact melt rock with rapid emplacement, hydrothermal alteration products, and observations of pore space, vugs, and vesicles. The uplifted granitic peak ring materials have values of 4000–4200 m/s, 2.39–2.44 g/cm3, and 8–13% for velocity, density, and porosity, respectively; these values differ significantly from typical unaltered granite which has higher velocity and density, and lower porosity. The majority of Hole M0077A peak-ring velocity, density, and porosity measurements indicate considerable rock damage, and are consistent with numerical model predictions for peak-ring formation where the lithologies present within the peak ring represent some of the most shocked and damaged rocks in an impact basin. We integrate our results with previous seismic datasets to map the suevite near the borehole. We map suevite below the Paleogene sedimentary rock in the annular trough, on the peak ring, and in the central basin, implying that, post impact, suevite covered the entire floor of the impact basin. Suevite thickness is 100–165 m on the top of the peak ring but 200 m in the central basin, suggesting that suevite flowed downslope from the collapsing central uplift during and after peak-ring formation, accumulating preferentially within the central basin.

¹Anne Pommier
Earth and Planetary Science Letters 496, 37-46. Link to Article [https://doi.org/10.1016/j.epsl.2018.05.032]
¹UC San Diego, Scripps Institution of Oceanography, Institute of Geophysics and Planetary Physics, La Jolla, CA, USA
Copyright Elsevier

Electrical experiments were performed on core analogues in the Fe–S system and on FeSi2 up to 8 GPa and 1850 °C in the multi-anvil apparatus. Electrical resistivity was measured using the four-electrode method. For all samples, resistivity increases with increasing temperature. The higher the S content, the higher the resistivity and the resistivity increase upon melting. At 4.5 GPa, liquid FeS is up to >10 times more resistive than Fe-5 wt.% S and twice more resistive than FeSi2, suggesting a stronger influence of S than Si on liquid resistivity. Electrical results are used to develop crystallization-resistivity paths considering both equilibrium and fractional crystallization in the Fe–S system. At 4.5 GPa, equilibrium crystallization, as expected locally in thin snow zones during top-down core crystallization, presents electrical resistivity variations from about 300 to 190 microhm-cm for a core analogue made of Fe-5 wt.%S, depending on temperature. Fractional crystallization, which is relevant to core-scale cooling, leads to more important electrical resistivity variations, depending on S distribution across the core, temperature, and pressure. Estimates of the lower bound of thermal resistivity are calculated using the Wiedemann–Franz law. Comparison with previous works indicates that the thermal conductivity of a metallic core in small terrestrial bodies is more sensitive to the abundance of alloying agents than that of the Earth’s core. Application to Ganymede using core adiabat estimates from previous studies suggests important thermal resistivity variations with depth during cooling, with a lower bound value at the top of the core that can be as low as 3 W/m K. It is speculated that the generation and sustainability of a magnetic field in small terrestrial bodies might be favored in light element-depleted cores.

¹S. E. Kichanov,¹D. P. Kozlenko,¹E. V. Lukin,¹A. V. Rutkauskas,²E. A. Krasavin,³A. Y. Rozanov, ¹B. N. Savenko
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13115]
¹FLNP, Joint Institute for Nuclear Research, Dubna, Russia
²Laboratory of Radiation Biology, Joint Institute for Nuclear Research, Dubna, Russia
³Paleontological Institute of Russian Academy of Sciences, Moscow, Russia
Published by Arrangement with John Wiley & Sons

The internal structure of an olivine‐rich fragment of the Seymchan meteorite was studied using neutron tomography. The differences in the neutron attenuation coefficients of constituent elements of the studied pallasite and the application of modern mathematical algorithms for a three‐dimensional (3‐D) imaging data analysis allow us to obtain a spatial distribution of different meteorite components. The heterogeneous distribution of the nickel in the metal phase was observed. In addition to the resulting 3‐D model of the Seymchan meteorite, the distributions of the volumes, average sizes, and shape‐related parameters of the FeNi metal component and olivine grains were obtained.

¹V.Petropoulou, ²M.Lazzarin, ²I.Bertini,^2,3P.Ochner, ²F.La Forgia,²A.Siviero, ¹F.Ferri,^1,2,4G.Naletto
Planetary and Space Science (in Press) Link to Article [https://doi.org/10.1016/j.pss.2018.05.003]
¹Centro di Ateneo di Studi ed Attivitá Spaziali ”Giuseppe Colombo” (CISAS), University of Padova, Via Venezia 15, I-35131, Padova, Italy
²Department of Physics and Astronomy “G. Galilei”, University of Padova, Vicolo dell’ Osservatorio 3, I-35122, Padova, Italy
³INAF – Osservatorio Astronomico di Padova, Vicolo Osservatorio 5, I-35122, Padova, Italy
⁴CNR-IFN UOS Padova LUXOR, Via Trasea 7, I-35131, Padova, Italy

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¹Bing Xiao, ¹Lars Stixrude
Proceeding sof the National Academy of Sciences of the United States of America (PNAS) 115, 5371-5376 Link to Article [https://doi.org/10.1073/pnas.1719134115]
¹Department of Earth Sciences, University College London, London WC1E 6BT, United Kingdom

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^1,2S. D. Crossley, ³N. G. Lunning, ⁴R. G. Mayne, ³T. J. McCoy, ⁴S. Yang, ⁴M. Humayun, ⁵R. D. Ash, ⁶J. M. Sunshine, ⁷R. C. Greenwood, ⁷I. A. Franchi
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13114]
¹Monnig Meteorite Collection, Texas Christian University, , Fort Worth, Texas, USA
²Department of Geology, University of Maryland, , Maryland, USA
³Department of Mineral Sciences, Smithsonian Institution, National Museum of Natural History, Washington, DC, USA
⁴National High Magnetic Field Laboratory and Department of Earth, Ocean & Atmospheric Science, Florida State University, Tallahassee, Florida, USA
⁵Department of Geology, University of Maryland, , Maryland, USA
⁶Department of Astronomy, University of Maryland, , Maryland, USA
⁷Planetary and Space Sciences, School of Physical Sciences, The Open University, Walton Hall, Milton Keynes, UK
Published by arrangement with John Wiley & Sons

The incompatible trace element‐enriched Stannern‐trend eucrites have long been recognized as requiring a distinct petrogenesis from the Main Group‐Nuevo Laredo (MGNL) eucrites. Barrat et al. (2007) proposed that Stannern‐trend eucrites formed via assimilation of crustal partial melts by a MGNL‐trend magma. Previous experimental studies of low‐degree partial melting of eucrites did not produce sufficiently large melt pools for both major and trace element analyses. Low‐degree partial melts produced near the solidus are potentially the best analog to the assimilated crustal melts. We partially melted the unbrecciated, unequilibrated MGNL‐trend eucrite NWA 8562 in a 1 atm gas‐mixing furnace, at IW‐0.5, and at temperatures between 1050 and 1200 °C. We found that low‐degree partial melts formed at 1050 °C are incompatible trace element enriched, although the experimental melts did not reach equilibrium at all temperatures. Using our experimental melt compositions and binary mixing modeling, the FeO/MgO trend of the resultant magmas coincides with the range of known Stannern‐trend eucrites when a primary magma is contaminated by crustal partial melts. When experimental major element compositions for eucritic crustal partial melts are combined with trace element concentrations determined by previous modeling (Barrat et al. 2007), the Stannern‐trend can be replicated with respect to both major, minor, and trace element concentrations.

^1,2Matthew J. Genge, ^1,2Matthias van Ginneken, ^1,2Martin D. Suttle, ³Ralph P. Harvey
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13107]
¹Department of Earth Science and Engineering, Imperial College London, , London, UK
²Department of Earth Science, The Natural History Museum, London, UK
³Department of Geological Sciences, Case Western Reserve University, Cleveland, Ohio, USA
Published by arrangement wit John Wiley & Sons

We report the discovery of a large accumulation of micrometeorites (MMs) in a supraglacial moraine at Larkman Nunatak in the Grosvenor Mountains of the Transantarctic Range in Antarctica. The MMs are present in abundances of ~600 particles kg−1 of moraine sediment and include a near‐complete collection of MM types similar to those observed in Antarctic blue ice and within bare‐rock traps in the Antarctic. The size distribution of the observed particles is consistent with those collected from snow collections suggesting the moraine has captured a representative collection of cosmic spherules with significant loss of only the smallest particles (<100 μm) by wind. The presence of microtektites with compositions similar to those of the Australasian strewn field suggests the moraine has been accumulating for 780 ka with dust‐sized debris. On the basis of this age estimate, it is suggested that accumulation occurs principally through ice sublimation. Direct infall of fines is suggested to be limited by snow layers that act as barriers to accumulation and can be removed by wind erosion. MM accumulation in many areas in Antarctica, therefore, may not be continuous over long periods and can be subject to climatic controls. On the basis of the interpretation of microtektites as Australasian, Larkman Nunatak deposit is the oldest known supraglacial moraine and its survival through several glacial maxima and interglacial periods is surprising. We suggest that stationary ice produced by the specific ice flow conditions at Larkman Nunatak explains its longevity and provides a new type of record of the East Antarctic ice sheet.

¹James Mortimer, ²Christophe Lécuyer, ²François Fourel, ³James Carpenter
Planetary and Space Science (in Press) Link to Article [https://doi.org/10.1016/j.pss.2018.05.010]
¹Planetary and Space Sciences, School of Physical Sciences, The Open University, Walton Hall, MK7 6AA, Milton Keynes, Buckinghamshire, United Kingdom
²Laboratoire de Géologie de Lyon, CNRS UMR 5276, Université Claude Bernard Lyon 1, 69622, Villeurbanne, France
³ESA ESTEC, Keplerlaan 1, 2401, AZ, Noordwijk, the Netherlands

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