¹Jian Chen, ²Tiekuang Dong, ^1,3Zhongzhou Ren
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12817]
¹Department of Physics and Key Laboratory of Modern Acoustics, Institute of Acoustics, Nanjing University, Nanjing, China
²Key Laboratory of Dark Matter and Space Astronomy, Purple Mountain Observatory, CAS, Nanjing, China
³Center of Theoretical Nuclear Physics, National Laboratory of Heavy-Ion Accelerator, Lanzhou, China
Published by arrangement with John Wiley & Sons

A physical model based on the open-source toolkit Geant4 for production rates of cosmogenic nuclei on the lunar surface is proposed and calibrated. The fluxes of proton and neutron beneath the lunar surface are obtained by simulating the physical processes between the cosmic-ray particles and the lunar surface material. By combining the experimental proton cross sections and the a posteriori neutron cross sections, we calculate the production rate depth profiles of long-lived nuclei (10Be, 14C, 26Al, 36Cl, and 53Mn). Through comparing experimental and theoretical data for these nuclei, we find that for all the selected nuclei, experimental and theoretical production rate depth profiles agree well with each other by introducing a single normalization factor. It means that the physical model based on Geant4 can also reproduce the depth profiles of cosmogenic nuclei, and that this model can be used by everyone worldwide. In addition, we predict the production rates of three stable nuclei (21Ne, 22Ne, and 38Ar).

¹I. S. Sanders, ²E. R. D. Scott, ³J. S. Delaney
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12820]
¹Department of Geology, Trinity College, Dublin 2, Ireland
²Hawai’i Institute of Geophysics and Planetology, University of Hawai’i at Mānoa, Honolulu, Hawaii, USA
³Department of Geological Sciences, Rutgers University, Piscataway, New Jersey, USA
Published by arrangement with John Wiley & Sons

Ureilite meteorites are abundant, carbon-rich, primitive achondrites made of coarse-grained, equilibrated olivine and pyroxene (usually pigeonite). They probably sample the baked, heterogeneous, melt-depleted mantle of a large, once-chondritic parent body that was broken up catastrophically while still young and hot. Heterogeneity in the parent body is inferred from a considerable “slope-1” variation from one meteorite to another in oxygen isotopes (−2.5‰ < Δ17O < −0.2‰), which correlates with both molar FeO/MgO (range 0.03–0.35) and molar FeO/MnO (range 3–57), i.e., Δ17O correlates with the redox state. No consensus has yet emerged on the cause of these correlated trends. One view favors their inheritance via silicates from hot nebular (preaccretion) processes. Another invokes smelting (reduction of FeO by C in the hot parent body). Here, guided mainly by similar trends among equilibrated ordinary and R chondrites, studies of their unequilibrated counterparts, and work on other primitive achondrites, we propose a new model for ureilites in which the parent body accreted nebular ice with high-∆17O, Mg-rich silicates with low ∆17O, and varying amounts of metallic iron. Water from the thawing ice then oxidized the metal yielding secondary FeO-bearing minerals with high ∆17O that, with metamorphism, became incorporated into the ureilite silicates. FeO/MgO, FeO/MnO, and ∆17O correlate because they rose in unison by amounts that varied spatially, depending on the local amount of metal that was oxidized. We suggest that the parent body was so large (radius ≫ 100 km) that smelting was inhibited and that carbon played a passive role in ureilite evolution. Although ureilites are regarded as complicated meteorites, we believe our analysis explains their mass-independent oxygen isotope trend and related FeO variation through well-understood processes and enlightens our understanding of the evolution of early planetesimals from cold, wet bodies to hot, dry ones.

¹Krzysztof Szopa, ¹Tomasz Brachaniec, ¹Łukasz Karwowski, ¹Tomasz Krzykawski
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12815]
¹Department of Geochemistry, Mineralogy and Petrography, Faculty of Earth Science, University of Silesia, Sosnowiec, Poland
Published by arrangement with John Wiley & Sons

Fossil iron meteorites are extremely rare in the geological sedimentary record. The paleometeorite described here is the first such finding at the Cretaceous-Paleogene (K-Pg) boundary. In the boundary clay from the outcrop at the Lechówka quarry (Poland), fragments of the paleometeorite were found in the bottom part of the host layer. The fragments of meteorite (2–6 mm in size) and meteoritic dust are metallic-gray in color and have a total weight of 1.8181 g. Geochemical and petrographic analyses of the meteorite from Lechówka reveal the presence of Ni-rich minerals with a total Ni amount of 2–3 wt%. The identified minerals are taenite, kamacite, schreibersite, Ni-rich magnetite, and Ni-rich goethite. No relicts of silicates or chromites were found. The investigated paleometeorite apparently represents an independent fall and does not seem to be derived from the K-Pg impactor. The high degree of weathering did not permit the chemical classification of the meteorite fragments. However, the recognized mineral inventory, lack of silicates, and their pseudomorphs and texture may indicate that the meteorite remains were an iron meteorite.

^1,2François Faure, ^1,2Laurent Tissandier, ^1,2Léa Florentin, ^3,4Karine Devineau
Geochimica et Cosmochimica Acta (in Press) Link to Article [http://dx.doi.org/10.1016/j.gca.2017.01.034]
¹Université de Lorraine, CRPG, UMR 7358, 15 rue Notre Dame des Pauvres F-54501 Vandoeuvre-lès-Nancy France
²CNRS, CRPG, UMR 7358, 15 rue Notre Dame des Pauvres F-54501 Vandoeuvre-lès-Nancy France
³Université de Lorraine, GeoRessources, UMR 7359, Faculté des Sciences et Technologies rue Jacques Callot BP 70239, F-54506 Vandoeuvre-lès-Nancy Cedex, France
⁴CNRS, GeoRessources, UMR 7359, Faculté des Sciences et Technologies rue Jacques Callot BP 70239, F-54506 Vandoeuvre-lès-Nancy Cedex, France
Copyright Elsevier

Rare silica-rich glass inclusions (69 < SiO2 < 82 wt.%) are described within magnesian olivines of porphyritic Type IA chondrules. These glass inclusion compositions are clearly out of equilibrium with their host Mg-olivines and their presence within the olivines is generally attributed to an unclear secondary process such as a late interaction with nebular gases. We performed dynamic crystallisation experiments that demonstrate that these Si-rich glass inclusions are actually magmatic in origin and were trapped inside olivines that crystallized slowly from a magma with a CI, i.e. solar, composition. Their silica-rich compositions are the consequence of the small volumes of inclusions, which inhibit the nucleation of secondary crystalline phase (Ca-poor pyroxene) but allow olivine to continue to crystallize metastably on the walls of the inclusions. We suggest that Si-rich glass inclusions could be the only reliable relicts of what were the first magmas of the solar system, exhibiting a CI, i.e. non-fractionated, composition.

¹Mario Fischer-Gödde, ¹Thorsten Kleine
Nature 541, 525-527 Link to Article [doi:10.1038/nature21045]
¹Institut für Planetologie, University of Münster, Wilhelm-Klemm-Strasse 10, 48149 Münster, Germany

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¹Nicolas Dauphas
Nature 541, 521-524 Link to Article [doi:10.1038/nature20830]
¹Origins Laboratory, Department of the Geophysical Sciences and Enrico Fermi Institute, The University of Chicago, 5734 South Ellis Avenue, Chicago, Illinois 60637, USA

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^1,2Philipp R. Heck, ^1,3Birger Schmitz, ⁴William F. Bottke, ^1,2Surya S. Rout, ⁵Noriko T. Kita, ³Anders Cronholm, ³Céline Defouilloy, ^6,7Andrei Dronov, ³Fredrik Terfelt
Nature Astronomy 1, 35 Link to Article [doi:10.1038/s41550-016-0035]
¹Robert A. Pritzker Center for Meteoritics and Polar Studies, The Field Museum of Natural History, 1400 South Lake Shore Drive, Chicago, Illinois 60605, USA
²Chicago Center for Cosmochemistry and Department of the Geophysical Sciences, The University of Chicago, 5734 South Ellis Avenue, Chicago, Illinois 60637, USA
³Astrogeobiology Laboratory, Department of Physics, Lund University, PO Box 118, SE-22100 Lund, Sweden
⁴Department of Space Studies, Southwest Research Institute, 1050 Walnut Street, Suite 300, Boulder, Colorado 80302, USA
⁵WiscSIMS, Department of Geoscience, University of Wisconsin-Madison, 1215 W. Dayton Street, Madison, Wisconsin 53706-1692, USA
⁶Geological Institute, Russian Academy of Sciences, Pyzhevsky Pereulok 7, 119017 Moscow, Russia
⁷Kazan (Volga Region) Federal University, Kremlevskaya ulitsa 18, 420008 Kazan, Russia

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¹S. Antonellini, ¹J. Bremer, ¹I. Kamp, ²P. Riviere-Marichalar, ^1,3F. Lahuis, ⁴W.-F. Thi, ⁵P. Woitke, ⁶R. Meijerink, ^1,7G. Aresu,¹M. Spaans
Astronomy & Astrophysics 597, A72 Link to Article [http://dx.doi.org/10.1051/0004-6361/201527820]
¹Kapteyn Astronomical Institute, Postbus 800, 9700 AV Groningen, The Netherlands
²Centro de Astrobiología (INTA-CSIC) – Depto. Astrofísica, POB 78, ESAC Campus, 28691 Villanueva de la Cañada, Spain
³SRON Netherlands Institute for Space Research, PO Box 800, 9700 AV Groningen, The Netherlands
⁴Max-Planck-Institut für extraterrestrische Physisk, Giessenbachstrasse 1, 85748 Garching, Germany
⁵St. Andrews University, School of Physics and Astronomy, St. Andrews KY16 9SS, UK
⁶Leiden Observatory, Leiden University, PO Box, 2300 RA Leiden, The Netherlands
⁷INAF–Osservatorio Astronomico di Cagliari, via della Scienza 5, 09047 Selargius, Italy

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¹Takuji Tsujimoto, ²Tetsuya Yokoyama, ³Kenji Bekki
The Astrophysical Journal Letters 835, L3 Link to Article [http://dx.doi.org/10.3847/2041-8213/835/1/L3]
¹National Astronomical Observatory of Japan, Mitaka-shi, Tokyo 181-8588, Japan
²Department of Earth and Planetary Sciences, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo 152-8551, Japan
³ICRAR, M468, The University of Western Australia, 35 Stirling Highway, Crawley Western Australia 6009, Australia

Meteoritic abundances of r-process elements are analyzed to deduce the history of chemical enrichment by the r-process, from the beginning of disk formation to the present time in the solar vicinity. Our analysis combines the abundance information from short-lived radioactive nuclei such as 244Pu with the abundance information from stable r-process nuclei such as Eu. These two types of nuclei can be associated with one r-process event and an accumulation of events until the formation of the solar system, respectively. With the help of the observed local star formation (SF) history, we deduce the chemical evolution of 244Pu and obtain three main results: (i) the last r-process event occurred 130–140 Myr before the formation of the solar system; (ii) the present-day low 244Pu abundance as measured in deep-sea reservoirs results from the low recent SF rate compared to ~4.5−5 Gyr ago; and (iii) there were ~15 r-process events in the solar vicinity from the formation of the Galaxy to the time of solar system’s formation and ~30 r-process events to the present time. Then, adopting the hypothesis that a neutron star (NS) merger is the r-process production site, we find that the ejected r-process elements are extensively spread out and mixed with interstellar matter, with a mass of $\sim 3.5\times {10}^{6}$ M ⊙, which is about 100 times larger than that for supernova ejecta. In addition, the event frequency of r-process production is estimated to be 1 per ~1400 core-collapse supernovae, which is identical to the frequency of NS mergers estimated from the analysis of stellar abundances.

¹Shigeru Wakita, ^1,2Yuji Matsumoto, ¹Shoichi Oshino, ³Yasuhiro Hasegawa
The Astrophysical Journal 834, 125 Link to Article [http://dx.doi.org/10.3847/1538-4357/834/2/125]
¹Center for Computational Astrophysics, National Astronomical Observatory of Japan, Mitaka, Tokyo 181-8588, Japan
²Planetary Exploration Research Center, Narashino, Chiba 275-0016, Japan
³Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA

Chondritic meteorites contain unique spherical materials named chondrules: sub-mm sized silicate grains once melted in a high temperature condition in the solar nebula. We numerically explore one of the chondrule forming processes—planetesimal collisions. Previous studies have found that impact jetting via protoplanet–planetesimal collisions can make chondrules with 1% of the impactors’ mass, when the impact velocity exceeds 2.5 km s−1. Based on the mineralogical data of chondrules, undifferentiated planetesimals would be more suitable for chondrule-forming collisions than potentially differentiated protoplanets. We examine planetesimal–planetesimal collisions using a shock physics code and find two things: one is that planetesimal–planetesimal collisions produce nearly the same amount of chondrules as protoplanet–planetesimal collisions (~1%). The other is that the amount of produced chondrules becomes larger as the impact velocity increases when two planetesimals collide with each other. We also find that progenitors of chondrules can originate from deeper regions of large targets (planetesimals or protoplanets) than small impactors (planetesimals). The composition of targets is therefore important, to fully account for the mineralogical data of currently sampled chondrules.