^1,2,3Valdes M.C.,^4,5Bermingham K.R.,⁶Huang S.,⁷Simon J.I.
Chemical Geology 581, 120396 Link to Article [DOI 10.1016/j.chemgeo.2021.120396]
¹Robert A. Pritzker Center for Meteoritics and Polar Studies, Negaunee Integrative Research Center, The Field Museum of Natural History, Chicago, IL, United States
²Department of Geophysical Sciences, The University of Chicago, Chicago, IL, United States
³Department of Earth Sciences, University of Cambridge, Cambridge, UK, United Kingdom
⁴Department of Earth and Planetary Science, Rutgers University, Piscataway, NJ, United States
⁵Department of Geology, University of Maryland, College Park, MD, United States
⁶Department of Geoscience, University of Nevada, Las Vegas, Las Vegas, NV, United States
⁷Center for Isotope Cosmochemistry and Geochronology, Astromaterials Research and Exploration Science, NASA Johnson Space Center, Houston, TX, United States

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^1,2,3McDonough W.F.,²Yoshizaki T.
Progress in Earth and Planetary Science 8, 39 Link to Article [DOI 10.1186/s40645-021-00429-4]
¹Department of Geology, University of Maryland, College Park, 8000 Regents Drive, College Park, 20742, MD, United States
²Department of Earth Science, Tohoku University, 6-3, Aoba, Aramaki, Aoba, Sendai, 980-8578, Japan
³Research Center of Neutrino Sciences, Tohoku University, 6-3, Aoba, Aramaki, Aoba, Sendai, 980-8578, Japan

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^1,2S.Cambioni et al. (>10)
Nature 598, 49–52 Link to Article [DOI https://doi.org/10.1038/s41586-021-03816-5]
¹Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ, USA
²Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA, USA

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¹Ian S. Sanders,²Edward R. D. Scott
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13742]
¹Department of Geology, Trinity College, Dublin 2, Ireland
²Hawai‘i Institute of Geophysics and Planetology, University of Hawai‘i at Mānoa, Honolulu, Hawai‘i, 96822 USA
Published by arrangement with John Wiley & Sons

The remarkable complementary isotopic relationship in the Allende chondrite between chondrules (depleted in s-process molybdenum and tungsten) and matrix (enriched in these nuclides) has been interpreted as evidence that the anomalies were established during chondrule formation, and that chondrules were, therefore, not made by planetesimal collisions. We question this interpretation, and to better understand the complementary relationship, we review nucleosynthetic isotopic variations of Mo and W in bulk carbonaceous chondrites, their components, and acid leachates extracted from them. Mo isotopic data almost always track a mixing line between pure s-process Mo and s-process-depleted Mo (i.e., with excess p-process and r-process Mo in a fixed ratio). Tungsten data track an equivalent mixing line. Guided by our review, we develop a model suggesting how the isotopic variations in Allende’s chondrules and matrix could be attributable to hydrothermal alteration in the parent body. In our model, anomalous Mo and W, both depleted in s-process isotopes, are easily leached from their carriers in the matrix, then transported in solution and precipitated preferentially in water-deficient components, such as chondrules, where the aqueous solvent is consumed. The model operates after accretion so does not inform chondrule-forming mechanisms. It also goes some way to explaining variations of Mo and W isotopes in Ca-Al-rich inclusions in Allende, and variations of s-process Mo in bulk carbonaceous chondrites.

¹Fridolin Spitzer,¹Christoph Burkhardt,²Francis Nimmo,¹Thorsten Kleine
Earth and Planetary Science Letters 576, 117211 Link to Article [https://doi.org/10.1016/j.epsl.2021.117211]
¹Institut für Planetologie, University of Münster, Wilhelm-Klemm-Str. 10, 48149 Münster, Germany
²Department of Earth and Planetary Sciences, University of California Santa Cruz, Santa Cruz, CA, 95064, USA
Copyright Elsevier

The 182Hf-182W chronology of iron meteorites provides crucial information on the timescales of accretion and differentiation of some of the oldest planetesimals of the Solar System. Determining accurate Hf-W model ages of iron meteorites requires correction for cosmic ray exposure (CRE) induced modifications of W isotope compositions, which can be achieved using in-situ neutron dosimeters such as Pt isotopes. Until now it has been assumed that all Pt isotope variations in meteorites reflect CRE, but here we show that some ungrouped iron meteorites display small nucleosynthetic Pt isotope anomalies. These provide the most appropriate starting composition for the correction of CRE-induced W isotope variations in iron meteorites from all major chemical groups, which leads to a ∼1 Ma upward revision of previously reported Hf-W model ages. The revised ages indicate that core formation in non-carbonaceous (NC) iron meteorite parent bodies occurred at ∼1–2 Ma after CAI formation, whereas most carbonaceous (CC) iron meteorite parent bodies underwent core formation ∼2 Ma later. We show that the younger CC cores have lower Fe/Ni ratios than the earlier-formed NC cores, indicating that core formation under more oxidizing conditions occurred over a more protracted timescale. Thermal modeling of planetesimals heated by 26Al-decay reveals that this protracted core formation timescale is consistent with a higher fraction of water ice in CC compared to NC planetesimals, implying that in spite of distinct core formation timescales, NC and CC iron meteorite parent bodies accreted about contemporaneously within ∼1 Ma after CAI formation, but at different radial locations in the disk.

^1,2Guy Libourel,¹Clément Ganino,¹Marco Delbo,³Mathieu Niezgoda,⁴Benjamin Remy,⁵Lionel Aranda,¹Patrick Michel
Monthly Notices of the Royal Astronomical Society 500, 1905–1920 Link to Article [https://doi.org/10.1093/mnras/staa3183]
¹Observatoire de la Côte d’Azur, CNRS, Laboratoire Lagrange, Université Côte d’Azur, UMR 7293, Boulevard de l’Observatoire, CS 34229, F-06304 Nice Cedex 4, France
²School of Ocean, Earth Science and Technology, Hawai‘i Institute of Geophysics and Planetology, University of Hawai‘i at Mānoa, Honolulu, HI 96821, USA
³Commissariat à l’Energie Atomique et aux Energies Alternatives, CEA/DES/ISAS/DM2S/STMF/LMEC, PC 47, F-91191 Gif-sur-Yvette cedex, France
⁴Université de Lorraine, Laboratoire d’Energétique et de Mécanique Théorique Appliquée, CNRS, UMR 7563, 2 avenue de la Forêt de Haye, TSA 60604, F-54518 Vandoeuvre-les-Nancy Cedex, France
⁵Département Chimie et Physique des Solides et des Surfaces, Institut Jean Lamour, Université de Lorraine, UMR 7198, F-54000 Nancy, France

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^1,2Yohei Igami,¹Shunsuke Muto,³Aki Takigawa,¹Masahiro Ohtsuka,²Akira Miyake,⁴Kohtaku Suzuki,⁵Keisuke Yasuda,^6,7,8Akira Tsuchiyama
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2021.09.031]
¹Institute of Materials and Systems for Sustainability, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603, Japan
²Division of Earth and Planetary Sciences, Kyoto University, Kitashirakawa-Oiwakecho, Sakyo-ku, Kyoto 606-8502, Japan
³Department of Earth and Planetary Science, The University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
⁴The Wakasa Wan Energy Research Center, Tsuruga, Fukui 914-0192, Japan
⁵Graduate School of Life and Environmental Science, Kyoto Prefectural University, Shimogamo-Hangicho, Sakyo-ku, Kyoto 606-8522, Japan
⁶Research Organization of Science and Technology, Ritsumeikan University, Kusatsu 525-8577, Japan
⁷CAS Key Laboratory of Mineralogy and Metallogeny/Guangdong Provincial Key Laboratory of Mineral Physics and Materials, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou, 510640, China
⁸CAS Center for Excellence in Deep Earth Science, Guangzhou 510640, China
Copyright Elsevier

Minerals on airless bodies exhibit characteristic spectral features such as darkening and reddening. Such space weathering is mainly due to hydrogen-ion irradiation by the solar wind and to micrometeorite impacts. Because of the reactivity of hydrogen, the associated H-implantation into O-bearing minerals can lead to the formation of new chemical bonds and may contribute to formation of water. However, laboratory studies still conflict about production efficiency of water and relevant H-bearing molecules such as OH formed by the H-ion irradiation. The production efficiency of the molecules within minerals may be influenced by short-range structural order of the host minerals. It is thus important to clarify how the implanted H interacts with various irradiation defects produced by H-ion bombardment. Here, we investigated H-ion-irradiated alumina (Al₂O₃), one of the most basic oxides, using scanning/transmission electron microscopy (S/TEM) and electron energy-loss spectroscopy (EELS). The TEM images revealed dense dislocations, nanoscale voids and nanoscale cracks—instead of amorphization—in the region subject to high energy deposition. Our analyses by STEM–EELS hyperspectral imaging (HSI) isolated a few essential spectral components, suggesting that chemical interactions between the implanted H and the host alumina resulted in local generation of OH species rather than amorphization. We also found a spectral feature which may be explained by H₂ gas, presumably remaining in the nanovoids, most of which escaped through fractures formed by the coalescence of the high-pressure H₂ nanobubbles. Such fractures/crack surfaces can act as additional reactive sites for the formation of the OH species. The present results strongly imply that H⁺ irradiation can be a source of water in minerals in various astrophysical conditions. The present methodology can be applied to a wide range of extraterrestrial materials, such as regolith grains, interplanetary-dust particles, and/or presolar grains in primitive meteorites.

¹Leanne G.Staddon,¹James R.Darling,²Winfried H.Schwarz,³Natasha R.Stephen,¹Sheila Schuindt,¹Joseph Dunlop,⁴Kimberly T.Tait
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2021.09.034]
¹School of the Environment, Geography and Geoscience, University of Portsmouth, Portsmouth, PO1 3QL, United Kingdom
²Institute of Earth Sciences, Heidelberg Ion Probe, Heidelberg University, 69120 Heidelberg, Germany
³Plymouth Electron Microscopy Centre, University of Plymouth, Plymouth, PL4 8AA, United Kingdom
⁴Department of Natural History, Royal Ontario Museum, Toronto, ON, M5S 2C6, Canada
Copyright Elsevier

Baddeleyite (monoclinic; m-ZrO2) is a widespread accessory phase within shergottites. However, the effects of shock loading on baddeleyite U-Pb isotopic systematics, and therefore its reliability as a geochronometer within highly shocked lithologies, are less well constrained. To investigate the effects of shock metamorphism on baddeleyite U-Pb chronology, we have conducted high-resolution microstructural analysis and in-situ U-Pb isotopic measurements for baddeleyite within enriched basaltic shergottites Northwest Africa (NWA) 7257, NWA 8679 and Zagami. Electron backscatter diffraction (EBSD) analyses of baddeleyite reveal significant microstructural heterogeneity within individual thin sections, recording widespread partial to complete reversion from high-pressure (≥ 3.3 GPa) orthorhombic zirconia polymorphs. We define a continuum of baddeleyite microstructures into four groupings on the basis of microstructural characteristics, including rare grains that retain magmatic twin relationships. Uncorrected U-Pb isotopic measurements form Tera-Wasserburg discordia, yielding new 238U-206Pb discordia ages of 195 ± 15 Ma (n = 17) for NWA 7257 and 220 ± 23 Ma (n = 10) for NWA 8679. Critically, there is no resolvable link between baddeleyite microstructure and U-Pb isotope systematics, indicating negligible open-system behaviour of U-Pb during zirconia phase transformations. Instead, we confirm that high post-shock temperatures exert the greatest control on Pb mobility within shocked baddeleyite; in the absence of high post-shock temperatures, baddeleyite yield robust U-Pb isotope systematics and date the age of magmatic crystallization. Low bulk post-shock temperatures recorded within Zagami (≤ 220 °C), and suggested within NWA 7257 and NWA 8679 by baddeleyite microstructure and other petrological constraints, confirm that the previously derived baddeleyite age of Zagami records magmatic crystallization, and provide greater age diversity to 225 Ma to 160 Ma enriched shergottites. While our data yield no resolvable link between microstructure and U-Pb isotopic composition, we strongly recommend that microstructural analyses should represent an essential step of baddeleyite U-Pb chronology within planetary (e.g., martian, lunar, asteroidal) and shocked terrestrial samples, allowing full contextualisation prior to destructive isotopic techniques. Microstructurally constrained in-situ U-Pb analyses of baddeleyite thus define new opportunities for the absolute chronology of martian meteorites and, more broadly, shocked planetary materials.

^1,2Paula Izquierdo,³Odette Toloza,^3,4Boris T Gänsicke,^1,2Pablo Rodríguez-Gil,⁵Jay Farihi,⁶Detlev Koester,⁵Jincheng Guo,⁷Seth Redfield
Monthly Notices of the Royal Astronomical Society  501, 4276–4288, Link to Article [https://doi.org/10.1093/mnras/staa3987]
¹Instituto de Astrofísica de Canarias, E-38205 La Laguna, Tenerife, Spain
²Departamento de Astrofísica, Universidad de La Laguna, E-38206 La Laguna, Tenerife, Spain
³Department of Physics, University of Warwick, Coventry CV4 7AL, UK
⁴Center for Exoplanets and Habitability, University of Warwick, Coventry CV4 7AL, UK
⁵Department of Physics and Astronomy, University College London, London WC1E 6BT, UK
⁶Institut für Theoretische Physik und Astrophysik, Universität Kiel, D-24098 Kiel, Germany
⁷Department of Astronomy and Van Vleck Observatory, Wesleyan University, Middletown, CT 06459, USA

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^1,2Vladimir V Busarev,³Elena V Petrova,¹Marina P Shcherbina,¹Natalia P Ikonnikova,¹Marina A Burlak,¹Alexander A Belinski
Monthly Notices of the Royal Astronomical Society 502, 1882-1894 Link to Article [https://doi.org/10.1093/mnras/staa4022]
¹Lomonosov Moscow State University, Sternberg Astronomical Institute (SAI MSU), Universitetskii 13, Moscow 119992, Russia
²Institute of Astronomy, Russian Academy of Science, Pyatnitskaya 48, Moscow 109017, Russia
³Space Research Institute, Russian Academy of Sciences (IKI RAS), Profsoyuznaya 84/32, Moscow 117997, Russia

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