Jens Hopp^1,2,*, Natalie Schröter¹, Olga Pravdivtseva³, Hans-Peter Meyer¹, Mario Trieloff^1,2 and Ulrich Ott^1,4,5

Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.13062]
¹Institut für Geowissenschaften, Universität Heidelberg, Heidelberg, Germany
²Klaus-Tschira-Labor für Kosmochemie, Heidelberg, Germany
³McDonnell Center for the Space Sciences and Physics Department of Washington University, Saint Louis, Missouri, USA
⁴MTA Atomki, Debrecen, Hungary
⁵Max-Planck-Institut für Chemie, Mainz, Germany
Published by arrangement with John Wiley & Sons

Northwest Africa (NWA) 7325 is an anomalous achondrite that experienced episodes of large-degree melt extraction and interaction with melt under reducing conditions. Its composition led to speculations about a Mercurian origin and provoked a series of studies of this meteorite. We present the noble gas composition, and results of ⁴⁰Ar/³⁹Ar and ¹²⁹I-¹²⁹Xe studies of whole rock splits of NWA 7325. The light noble gases are dominated by cosmogenic isotopes. ²¹Ne and ³⁸Ar cosmic-ray exposure ages are 25.6 and 18.9 Ma, respectively, when calculated with a nominal whole rock composition. This ³⁸Ar age is in reasonable agreement with a cosmic-ray exposure age of 17.5 Ma derived in our ⁴⁰Ar/³⁹Ar dating study. Due to the low K-content of 19 ± 1 ppm and high Ca-content of approximately 12.40 ± 0.15 wt%, no reliable ⁴⁰Ar/³⁹Ar age could be determined. The integrated age strongly depends on the choice of an initial ⁴⁰Ar/³⁶Ar ratio. An air-like component is dominant in lower temperature extractions and assuming air ⁴⁰Ar/³⁶Ar for the trapped component results in a calculated integrated age of 3200 ± 260 (1σ) Ma. This may represent the upper age limit for a major reheating event affecting the K-Ar system. Results of ¹²⁹I-¹²⁹Xe dating give no useful chronological information, i.e., no isochron is observed. Considering the highest ¹²⁹Xe*/¹²⁸Xe_I ratio as equivalent to a lower age limit, we calculate an I-Xe age of about 4536 Ma. In addition, elevated ¹²⁹Xe/¹³²Xe ratios of up to 1.65 ± 0.18 in higher temperature extractions indicate an early formation of NWA 7325, with subsequent disturbance of the I-Xe system.

E. B. Bierhaus^1,*, A. S. McEwen², S. J. Robbins³, K. N. Singer³, L. Dones³, M. R. Kirchoff³ and J.-P. Williams⁴

Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.13057]
¹Lockheed Martin Space, Denver, Colorado, USA
²University of Arizona, Tucson, Arizona, USA
³Southwest Research Institute, Boulder, Colorado, USA
⁴University of California, Los Angeles, California, USA
Published by arrangement with John Wiley & Sons

We review the secondary-crater research over the past decade, and provide new analyses and simulations that are the first to model an accumulation of a combined primary-plus-secondary crater population as discrete cratering events. We develop the secondary populations by using scaling laws to generate ejecta fragments, integrating the trajectories of individual ejecta fragments, noting the location and velocity at impact, and using scaling laws to estimate secondary-crater diameters given the impact conditions. We also explore the relationship between the impactor size–frequency distribution (SFD) and the resulting secondary-crater SFD. Our results from these analyses indicate that the “secondary effect” varies from surface to surface and that no single conclusion applies across the solar system nor at any given moment in time—rather, there is a spectrum of outcomes both spatially and temporally, dependent upon target parameters and the impacting population. Surface gravity and escape speed define the spatial distribution of secondaries. A shallow-sloped impactor SFD will cause proportionally more secondaries than a steeper-sloped SFD. Accounting for the driving factors that define the magnitude and spatial distribution of secondaries is essential to determine the relative population of secondary craters, and their effect on derived surface ages.

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¹Allison M McGraw, ¹Vishnu Reddy, ²Juan A Sanchez
Monthly Notices of the Royal Astronomical Society 476, 630–634, Link to Article [https://doi.org/10.1093/mnras/sty250]
¹Lunar and Planetary Lab, The University of Arizona, 1629 E University Blvd, Tucson, AZ 85721, USA
²Planetary Science Institute, 1700 E Ft. Lowell, Tucson, AZ 85719, USA

We currently do not have a copyright agreement with this publisher and cannot display the abstract here

¹Lucille Le Corre, ¹Juan A Sanchez, ²Vishnu Reddy, ^3,4Driss Takir, ⁵Edward A Cloutis, ⁶Audrey Thirouin, ⁷Kris J Becker, ¹Jian-Yang Li, ⁸Seiji Sugita, ⁸Eri Tatsumi
Monthly Notices of the Royal Astronomical Society 475,614–623, Link to Article [https://doi.org/10.1093/mnras/stx3236]
¹Planetary Science Institute, 1700 E Fort Lowell Road, Tucson, AZ 85719, USA
²Lunar and Planetary Laboratory, University of Arizona, 1629 E University Blvd, Tucson, AZ 85721, USA
³SETI Institute, 89 Bernardo Ave, Suite 200, Mountain View, CA 94043, USA
⁴Visiting Astronomer at the Infrared Telescope Facility, which is operated by the University of Hawaii under contract NNH14CK55B with the National Aeronautics and Space Administration
⁵Department of Geography, University of Winnipeg, 515 Portage Avenue, Winnipeg, Manitoba R3B 2E9, Canada
⁶Lowell Observatory, 1400 W Mars Hill Rd, Flagstaff, AZ 86001, USA
⁷USGS Astrogeology Science Center, 2255 N. Gemini Drive, Flagstaff, AZ 86001, USA
⁸Department of Earth and Planetary Science, School of Science, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan

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¹James R. Lyons, ²Ehsan Gharib-Nezhad, ¹Thomas R. Ayres
Nature Communications 9, 908 Link to Article [doi:10.1038/s41467-018-03093-3doi:10.1038/s41467-018-03093-3]
¹School of Earth and Space Exploration, Arizona State University, 781 S. Terrace Rd, Tempe, AZ, 85281, USA
²School of Molecular Sciences, Arizona State University, Tempe, AZ, 85287, USA
³Center for Astrophysics and Space Astronomy, University of Colorado, Boulder, CO, 80309, USA

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¹Alessandra Migliorini,¹M. C. De Sanctis,²D. Lazzaro,³E. Ammannito
Monthly Notices of the Royal Astronomical Society, 475, 353–358 Link to Article [https://doi.org/10.1093/mnras/stx3193]
¹Institute of Space Astrophysics and Planetology, IAPS-INAF, I-00133 Rome, Italy
²Observatório Nacional, COAA, 20921-400 Rio de Janeiro, Brazil
³Italian Space Agency, ASI, I-00133 Rome, Italy

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^1,2Paolo A. Sossi, ³Oliver Nebel, ¹Hugh St.C.O’Neill, ²FrédéricMoynier
Chemical Geology 477, 73-84 Link to Article [https://doi.org/10.1016/j.chemgeo.2017.12.006]
¹Research School of Earth Sciences, Australian National University, Acton 2601, ACT, Australia
²Institut de Physique du Globe de Paris, Sorbonne Paris Cité, Université Paris Diderot, CNRS, F-75005 Paris, France
³School of Earth, Atmosphere and Environment, Monash University, Clayton 3800, VIC, Australia

We currently do not have a copyright agreement with this publisher and cannot display the abstract here

^1,2Maurizio Pajola, ²Ted Roush, ^2,3Cristina Dalle Ore, ⁴Giuseppe A. Marzo, ⁵Emanuele Simioni
Planetary and Space Science (in Press) Link to Article [https://doi.org/10.1016/j.pss.2018.02.016]
¹Universities Space Research Association, NASA NPP Program1, USA
²NASA Ames Research Center, Moffett Field, CA, 94035, USA
³Carl Sagan Center, SETI Institute, Mountain View, CA, 94043, USA
⁴ENEA C. R. Casaccia, 00123, Roma, Italy
⁵INAF, Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, 35122, Padova, Italy

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^1,2,3,4M. Van Ginneken, ¹M.J. Genge, ⁵R.P. Harvey
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2018.02.041]
¹IARC, Department of Earth Science and Engineering, Imperial College London, Exhibition Road, London SW7 2AZ, UK
²Department of Earth Science, The Natural History Museum, London SW7 2BT, UK
³Department of Analytical, Environmental and Geo-Chemistry, Vrije Universiteit Brussel, Pleinlaan 2, 1050 Brussel, Belgium1
⁴Laboratoire G-Time, Université Libre de Bruxelles, Franklin Rooseveltlaan 50, 1050 Brussel, Belgium1
⁵Department of Geological Sciences, 112 A. W. Smith Building, Case Western Reserve University, Cleveland, OH 44106-7216, USA
Copyright Elsevier

We report on the discovery of microtektites (microscopic impact glass spherules) in a glacial moraine near Larkman Nunatak in the Transantarctic Mountains, Antarctica. The microtektites were identified based on their physical and chemical properties. Major and trace element compositions of the particles suggest that they may be related to the Australasian strewn field. This would further extend the current strewn field ∼800 km southward. Depletion in volatiles and enrichment in refractory elements in Larkman Nunatak microtektites fit the volatilization trend defined by Australasian microtektites, suggesting that they may represent a new highly vapor fractionated end-member thereof. This observation is supported by their low vesicularity and absence of mineral inclusions. This discovery has significant implications for the formation of microtektites (i.e. their evolution with respect to the distance from the source crater). Finally, the discovery of potentially old (i.e. 0.8 Ma) microtektites in moraine has implications for the stability of the East Antarctic Ice Sheet in the Larkman Nunatak area over the last ∼1 Ma and, as a consequence, the high efficiency of such moraines as traps for other extraterrestrial materials (e.g. micrometeorites and meteoritic ablation debris).