^1,2G.K.Benedix et al. (>10)*
Geochmica et Cosmochimica Acta (in Press) Link to Article [http://dx.doi.org/10.1016/j.gca.2017.03.030]
¹Curtin University, Applied Geology, Bentley, Western Australia, Australia
²Western Australia Museum, Department of Earth and Planetary Sciences, Welshpool, Western Australia,
*Find the extensive, full author and affiliation list on the publishers website
Copyright Elsevier

Bunburra Rockhole is the first recovered meteorite of the Desert Fireball Network. We expanded a bulk chemical study of the Bunburra Rockhole meteorite to include major, minor and trace element analyses, as well as oxygen and chromium isotopes, in several different pieces of the meteorite. This was to determine the extent of chemical heterogeneity and constrain the origin of the meteorite. Minor and trace element analyses in all pieces are exactly on the basaltic eucrite trend. Major element analyses show a slight deviation from basaltic eucrite compositions, but not in any systematic pattern. New oxygen isotope analyses on 23 pieces of Bunburra Rockhole shows large variation in both δ17O and δ18O, and both are well outside the HED parent body fractionation line. We present the first Cr isotope results of this rock, which are also distinct from a majority of HEDs. Detailed computed tomographic scanning and back-scattered electron mapping do not indicate the presence of any other meteoritic contaminant (contamination is also unlikely based on trace element chemistry). We therefore conclude that Bunburra Rockhole represents a sample of a new differentiated asteroid, one that may have more variable oxygen isotopic compositions than 4 Vesta. The fact that Bunburra Rockhole chemistry falls on the eucrite trend perhaps suggests that multiple objects with basaltic crusts accreted in a similar region of the Solar System.

¹Max Collinet, ²Bernard Charlier, ³Olivier Namur, ³Martin Oeser, ^4,5Etienne Médard, ³Stefan Weyer
Geochimica et Cosmochimica Acta (in Press) Link to Article [http://dx.doi.org/10.1016/j.gca.2017.03.029]
¹Department of Earth, Atmospheric, and Planetary Science, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
²Département de Géologie, Université de Liège, 4000 Sart Tilman, Belgium
³Institut für Mineralogie, Leibniz Universität Hannover, 30167 Hannover, Germany
⁴Lunar and Planetary Institute, 3600 Bay Area Boulevard, Houston TX 77058, USA
⁵Laboratoire Magmas et Volcans, Université Blaise Pascal-CNRS-IRD, 63178 Aubière, France
Copyright Elsevier

Martian meteorites are the only samples available from the surface of Mars. Among them, olivine-phyric shergottites are basalts containing large zoned olivine crystals with highly magnesian cores (Fo 70-85) and rims richer in Fe (Fo 45-60). The Northwest Africa 1068 meteorite is one of the most primitive “enriched” shergottites (high initial 87Sr/86Sr and low initial ε143Nd). It contains olivine crystals as magnesian as Fo 77 and is a major source of information to constrain the composition of the parental melt, the composition and depth of the mantle source, and the cooling and crystallization history of one of the younger magmatic events on Mars (∼180 Ma). In this study, Fe-Mg isotope profiles analyzed in situ by femtosecond-laser ablation MC-ICP-MS are combined with compositional profiles of major and trace elements in olivine megacrysts. The cores of olivine megacrysts are enriched in light Fe isotopes (δ56FeIRMM-14 = -0.6 to -0.9 ‰) and heavy Mg isotopes (δ26MgDSM-3 = 0 to 0.2 ‰) relative to megacryst rims and to the bulk martian isotopic composition (δ56Fe = 0±0.05 ‰, δ26Mg = -0.27±0.04 ‰). The flat forsterite profiles of megacryst cores associated with anti-correlated fractionation of Fe-Mg isotopes indicate that these elements have been rehomogenized by diffusion at high temperature. We present a 1-D model of simultaneous diffusion and crystal growth that reproduces the observed element and isotope profiles. The simulation results suggest that the cooling rate during megacryst core crystallization was slow (43±21 °C/year), and consistent with pooling in a deep crustal magma chamber. The megacryst rims then crystallized 1 to 2 orders of magnitude faster during magma transport towards the shallower site of final emplacement. Megacryst cores had a forsterite content 3.2±1.5 mol% higher than their current composition and some were in equilibrium with the whole-rock composition of NWA 1068 (Fo 80±1.5). NWA 1068 composition is thus close to a primary melt (i.e. in equilibrium with the mantle) from which other enriched shergottites derived.

^1,2Laura Schaefer, ³Stein B. Jacobsen, ³John L. Remo, ^1,3M. I. Petaev, ¹Dimitar D. Sasselov
The Astrophysical Journal 835, 234 Link to Article [https://doi.org/10.3847/1538-4357/835/2/234]
¹Harvard-Smithsonian Center for Astrophysics, 60 Garden St., Cambridge, MA 02138, USA
²Arizona State University, School of Earth and Space Exploration, Tempe, AZ 85287, USA
³Harvard University, Department of Earth and Planetary Sciences, 20 Oxford St., Cambridge, MA 02138, USA

We use a thermodynamic framework for silicate-metal partitioning to determine the possible compositions of metallic cores on super-Earths. We compare results using literature values of the partition coefficients of Si and Ni, as well as new partition coefficients calculated using results from laser shock-induced melting of powdered metal-dunite targets at pressures up to 276 GPa, which approaches those found within the deep mantles of super-Earths. We find that larger planets may have little to no light elements in their cores because the Si partition coefficient decreases at high pressures. The planet mass at which this occurs will depend on the metal-silicate equilibration depth. We also extrapolate the equations of state (EOS) of FeO and FeSi alloys to high pressures, and present mass–radius diagrams using self-consistent planet compositions assuming equilibrated mantles and cores. We confirm the results of previous studies that the distribution of elements between mantle and core will not be detectable from mass and radius measurements alone. While observations may be insensitive to interior structure, further modeling is sensitive to compositionally dependent properties, such as mantle viscosity and core freeze-out properties. We therefore emphasize the need for additional high pressure measurements of partitioning as well as EOSs, and highlight the utility of the Sandia Z-facilities for this type of work.

¹Carles E. Moyano-Cambero, ²Eva Pellicer, ¹Josep M. Trigo-Rodríguez, ³Iwan P. Williams, ⁴Jürgen Blum, ⁵Patrick Michel, ⁶Michael Küppers, ¹Marina Martínez-Jiménez, ¹Ivan Lloro, ⁷Jordi Sort
The Astrophysical Journal 835, 2 Link to Article [https://doi.org/10.3847/1538-4357/835/2/157]
¹Institute of Space Sciences (IEEC-CSIC), Meteorites, Minor Bodies and Planetary Sciences Group, Campus UAB Bellaterra, c/Can Magrans s/n, 08193 Cerdanyola del Vallès (Barcelona), Spain
²Departament de Física, Universitat Autónoma de Barcelona, E-08193 Bellaterra, Spain
³School of Physics and Astronomy, Queen Mary, University of London, 317 Mile End Road, E1 4NS London, UK
⁴Institut für Geophysik und extraterrestrische Physik, Technische Universität Braunschweig, Mendelssohnstr. 3, D-38106 Braunschweig, Germany
⁵Lagrange Laboratory, University of Nice, CNRS, Côte d’Azur Observatory, France
⁶European Space Agency, European Space Astronomy Centre, P.O. Box 78, Villanueva de la Cañada E-28691, Spain
⁷Institució Catalana de Recerca i Estudis Avançats (ICREA) and Departament de Física, Universitat Autónoma de Barcelona, E-08193 Bellaterra, Spain

The Chelyabinsk meteorite is a highly shocked, low porosity, ordinary chondrite, probably similar to S- or Q-type asteroids. Therefore, nanoindentation experiments on this meteorite allow us to obtain key data to understand the physical properties of near-Earth asteroids. Tests at different length scales provide information about the local mechanical properties of the minerals forming this meteorite: reduced Young’s modulus, hardness, elastic recovery, and fracture toughness. Those tests are also useful to understand the potential to deflect threatening asteroids using a kinetic projectile. We found that the differences in mechanical properties between regions of the meteorite, which increase or reduce the efficiency of impacts, are not a result of compositional differences. A low mean particle size, attributed to repetitive shock, can increase hardness, while low porosity promotes a higher momentum multiplication. Momentum multiplication is the ratio between the change in momentum of a target due to an impact, and the momentum of the projectile, and therefore, higher values imply more efficient impacts. In the Chelyabinsk meteorite, the properties of the light-colored lithology materials facilitate obtaining higher momentum multiplication values, compared to the other regions described for this meteorite. Also, we found a low value of fracture toughness in the shock-melt veins of Chelyabinsk, which would promote the ejection of material after an impact and therefore increase the momentum multiplication. These results are relevant to the growing interest in missions to test asteroid deflection, such as the recent collaboration between the European Space Agency and NASA, known as the Asteroid Impact and Deflection Assessment mission.

¹Olivier Poch, ²Joachim Frey, ³Isabel Roditi, ⁴Antoine Pommerol, ⁴Bernhard Jost, ⁴Nicolas Thomas
Astrobiology 17, 231-252 Link to Article [doi:10.1089/ast.2016.1523]
¹Center for Space and Habitability, Universität Bern, Bern, Switzerland.
²Institute of Veterinary Bacteriology, University of Bern, Bern, Switzerland.
³Institut für Zellbiologie (IZB), Bern, Switzerland.
⁴Physikalisches Institut, Universität Bern, Bern, Switzerland.

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¹K. Bloxam, ²M. Campbell-Brown
Planetary and Space Science (in Press) Link to Article [http://dx.doi.org/10.1016/j.pss.2017.02.017]
¹McGill University, Department of Atmospheric and Oceanic Sciences, Montréal, QC, Canada H3A 0B9
²University of Western Ontario, Department of Physics and Astronomy, London, ON, Canada N6A 3K7

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

J. E. CHAPPELOW
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12853]
Meteorifics Inc., 1148 Sundance Loop, Fairbanks, Alaska 99709, USA
Published by Arrangement with John Wiley & Sons

Recent work on the shapes of small, simple impact craters on the Moon has shown that the parabolic ideal does not well represent the vast majority of these craters. They are hyperbolic in shape and usually resemble a cone more than a parabola. A parabolic shape also does not fit the most commonly held archetype for simple craters in general (Linné), which is also hyperbolic. In addition, Linné itself may not be the best model for fresh simple craters, in terms of cross-sectional shape, although shape data to compare it to have heretofore been lacking. Here, the “free shadowfront method” for determining the shapes of simple craters is used to measure 64 fresh simple craters on five lunar maria to test both assumptions. Laser altimetry cross sections, available for many of the craters measured herein, are used to complement and spot-check the shadow measurement results, and thereby demonstrate the efficacy of the free shadowfront method. A new shape model is established, and two craters that better fit this model than Linné are identified. These are located at 24.45° N/328.12° E and 31.35° N/296.46° E and have diameters of 1.40 and 2.73 km, respectively. An apparent dichotomy between fresh simple craters smaller than 2.5 km and those larger than this is observed. Flat floors are found to be ubiquitous among the larger craters, but rare and small in extent in smaller ones. A slide in one crater which appears to be an incipient flat floor suggests a major mode of formation for these flat floors.

¹Clemens M. RUMPF, ¹Hugh G. LEWIS, and ^2,3,4Peter M. ATKINSON
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12861]
¹Atronautics Research Group, Faculty of Engineering and the Environment, University of Southampton, Southampton, UK
²Faculty of Science and Technology, Lancaster University, Lancaster, UK
³Geography and Environment, University of Southampton, Southampton, UK
⁴School of Geography, Archaeology and Palaeoecology, Queen’s University Belfast, Belfast, UK
Published by Arrangement with John Wiley & Sons

An asteroid impact is a low probability event with potentially devastating consequences. The Asteroid Risk Mitigation Optimization and Research (ARMOR) software tool calculates whether a colliding asteroid experiences an airburst or surface impact and calculates effect severity as well as reach on the global map. To calculate the consequences of an impact in terms of loss of human life, new vulnerability models are derived that connect the severity of seven impact effects (strong winds, overpressure shockwave, thermal radiation, seismic shaking, ejecta deposition, cratering, and tsunamis) with lethality to human populations. With the new vulnerability models, ARMOR estimates casualties of an impact under consideration of the local population and geography. The presented algorithms and models are employed in two case studies to estimate total casualties as well as the damage contribution of each impact effect. The case studies highlight that aerothermal effects are most harmful except for deep water impacts, where tsunamis are the dominant hazard. Continental shelves serve a protective function against the tsunami hazard caused by impactors on the shelf. Furthermore, the calculation of impact consequences facilitates asteroid risk estimation to better characterize a given threat, and the concept of risk as well as its applicability to the asteroid impact scenario are presented.

^1,2Antoine S. G. Roth,³Reto Trappitsch,⁴Knut Metzler,⁵Beda A. Hofmann,¹Ingo Leya
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12868]
¹Institute of Physics, University of Bern, Bern, Switzerland
²Present Address: Department of Earth Sciences, ETH Zurich, Zurich, Switzerland
³Department of the Geophysical Sciences, The University of Chicago and Chicago Center for Cosmochemistry, Chicago, USA
⁴Institute for Planetology, University of M€unster, Muenster, Germany
⁵Natural History Museum Bern, Bern, Switzerland
Published by Arrangement with John Wiley & Sons

Solar-cosmic-ray-produced Ne (SCR-Ne), in the form of low cosmogenic ²¹Ne/²²Ne ratios (²¹Ne/²²Ne_cos <0.8), is more likely to be found in rare meteorite classes, like Martian meteorites, than in ordinary chondrites. This may be the result of a sampling bias: SCR-Ne is better preserved in meteorites with small preatmospheric radii and these specimens are often only studied if they belong to unusual or rare classes. We measured He and Ne isotopic concentrations and nuclear tracks in 25 small unpaired ordinary chondrites from Oman. Most chondrites have been intensively heated during atmospheric entry as evidenced by the disturbed track records, the low ³He/²¹Ne ratios, the low ⁴He concentrations, and the high peak release temperatures. Concentration depth profiles indicate significant degassing; however, the Ne isotopes are mainly undisturbed. Remarkably, six chondrites have low ²¹Ne/²²Ne_cos in the range 0.711–0.805. Using a new physical model for the calculation of SCR production rates, we show that four of the chondrites contain up to ~20% of SCR-Ne; they are analyzed in terms of preatmospheric sizes, cosmic ray exposure ages, mass ablation losses, and orbits. We conclude that SCR-Ne is preserved, regardless of the meteorite class, in specimens with small preatmospheric radii. Sampling bias explains the predominance of SCR-Ne in rare meteorites, although we cannot exclude that SCR-Ne is more common in Martian meteorites than it is in small ordinary chondrites.

^1,2Eva-Regine Carl,³Ulrich Mansfeld,⁴Hanns-Peter Liermann,²Andreas Danilewsky,³Falko Langenhorst,^5,6Lars Ehm,^4,7Ghislain Trullenque,¹Thomas Kenkmann
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12840]
¹Institut für Geo- und Umweltnaturwissenschaften, Geologie, Albert-Ludwigs-Universität, Albertstr. 23b, 79104 Freiburg,Germany2
²Institut für Geo- und Umweltnaturwissenschaften, Kristallographie, Albert-Ludwigs-Universität, Hermann-Herder-Str. 5, 79104 Freiburg, Germany
³Institut für Geowissenschaften, Mineralogie, Friedrich-Schiller-Universität Jena, Carl-Zeiss-Promenade 10, 07745 Jena, Germany
⁴DESY, Notkestraße 85, 22607 Hamburg, Germany
⁵Stony Brook University, Mineral Physics Institute, Stony Brook, NY 11794-2100, USA
⁶National Synchrotron Light Source II, Brookhaven National Laboratory, Upton, NY 11973-500, USA
⁷Institut Polytechnique LaSalle Beauvais, Departement GEOS,equipe B2R 19 rue Pierre Waguet – BP 30313, 60026 BeauvaisCedex, France
Published by Arrangement with John Wiley & Sons

Hypervelocity collisions of solid bodies occur frequently in the solar system and affect rocks by shock waves and dynamic loading. A range of shock metamorphic effects and high-pressure polymorphs in rock-forming minerals are known from meteorites and terrestrial impact craters. Here, we investigate the formation of high-pressure polymorphs of α-quartz under dynamic and nonhydrostatic conditions and compare these disequilibrium states with those predicted by phase diagrams derived from static experiments under equilibrium conditions. We create highly dynamic conditions utilizing a mDAC and study the phase transformations in α-quartz in situ by synchrotron powder X-ray diffraction. Phase transitions of α-quartz are studied at pressures up to 66.1 and different loading rates. At compression rates between 0.14 and 1.96 GPa s⁻¹, experiments reveal that α-quartz is amorphized and partially converted to stishovite between 20.7 GPa and 28.0 GPa. Therefore, coesite is not formed as would be expected from equilibrium conditions. With the increasing compression rate, a slight increase in the transition pressure occurs. The experiments show that dynamic compression causes an instantaneous formation of structures consisting only of SiO₆ octahedra rather than the rearrangement of the SiO₄tetrahedra to form a coesite. Although shock compression rates are orders of magnitude faster, a similar mechanism could operate in impact events.