^1,2R.Jaumann et al. (>10)
Science 365, 817-820 Link to Article [DOI: 10.1126/science.aaw8627]
¹German Aerospace Center (DLR), Institute of Planetary Research, Berlin, Germany.
²Free University of Berlin, Institute of Geosciences, Berlin, Germany.
Reprinted with permission from AAAS

The near-Earth asteroid (162173) Ryugu is a 900-m-diameter dark object expected to contain primordial material from the solar nebula. The Mobile Asteroid Surface Scout (MASCOT) landed on Ryugu’s surface on 3 October 2018. We present images from the MASCOT camera (MASCam) taken during the descent and while on the surface. The surface is covered by decimeter- to meter-sized rocks, with no deposits of fine-grained material. Rocks appear either bright, with smooth faces and sharp edges, or dark, with a cauliflower-like, crumbly surface. Close-up images of a rock of the latter type reveal a dark matrix with small, bright, spectrally different inclusions, implying that it did not experience extensive aqueous alteration. The inclusions appear similar to those in carbonaceous chondrite meteorites.

^1,2De Carvalho, W.P.,^1,2Rios, D.C.,³Zucolotto, M.E.,^1,2,4Conceição, H.,⁵Tosi, A.A.,²Gomes, M.M.
Pesquisas em Geosciencias 45, e0666 Link to Article [DOI: 10.22456/1807-9806.88647]
¹Universidade Federal da Bahia, Rua Barão de Jeremoabo, 147, Salvador, BA CEP 40.170-115, Brazil
²Grupo de Pesquisa Laboratório de Petrologia Aplicada à Pesquisa Mineral, Rua Barão de Jeremoabo, 147, Salvador, BA CEP 40.170-115, Brazil
³Museu Naciona, Universidade Federal do Rio de Janeiro, Quinta da Boa Vista. São Cristóvão, Rio de Janeiro, RJ CEP 20940-040, Brazil
⁴Universidade Federal de Sergipe, Av. Marechal Rondon, Jardim Rosa Elze, São Cristóvão, SE CEP 49.100-000, Brazil
⁵Labsonda, Instituto de Geociências, Universidade Federal do Rio de Janeiro, Av. Athos da Silveira Ramos, 274, Cidade Universitária, Ilha do Fundão, Rio de Janeiro, RJ CEP 21044-020, Brazil

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¹Barrat, J.-A.,²Bachèlery, P.
Lithos 344-345, 452-463 Link to Article [DOI: 10.1016/j.lithos.2019.07.009]
¹Univ Brest, CNRS, UMR 6538 (Laboratoire Géosciences Océan), Institut Universitaire Européen de la Mer (IUEM), Place Nicolas Copernic, Plouzané, 29280, France
²Université Clermont Auvergne, CNRS, IRD, OPGC, Laboratoire Magmas et Volcans, 6 avenue Blaise Pascal, Aubière, 63178, France

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¹Yogita Kadlag,¹Harry Becker,¹Andreas Harbott
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13375]
¹Institut für Geologische Wissenschaften, Freie Universität Berlin, Malteserstr. 74‐100, 12249 Berlin, Germany
Published by arrangement with John Wiley & Sons

Chromium isotopic data of physically separated components (chondrules, CAIs, variably magnetic size fractions) of the carbonaceous chondrites Allende and Murchison and bulk rock data of Allende, Ivuna, and Orgueil are reported to evaluate the origin of isotopic heterogeneity in these meteorites. Allende components show ε53Cr and ε54Cr from −0.23 ± 0.07 to 0.37 ± 0.05 and from −0.43 ± 0.08 to 3.7 ± 0.1, respectively. In components of Murchison, ε53Cr and ε54Cr vary from −0.06 ± 0.08 to 0.5 ± 0.1 and from 0.7 ± 0.2 to 1.7 ± 0.1, respectively. The non‐systematic variations of ε53Cr and 55Mn/52Cr in the components of Allende and Murchison were likely caused by small‐scale, alteration‐related redistribution of Mn >20 Ma after formation of the solar system. Chondrule fractions show the lowest 55Mn/52Cr and ε54Cr values of all components, consistent with evaporation of Mn and ε54Cr‐rich carrier phases from chondrule precursors. Components other than the chondrules show higher Mn/Cr and ε54Cr, suggestive of chemical and isotopic complementarity between chondrules and matrix‐rich fractions. Bulk rock compositions calculated based on weighted compositions of components agree with measured Cr isotope data of bulk rocks, in spite of the Cr isotopic heterogeneity reported by the present and previous studies. This indicates that on a sampling scale comprising several hundred milligrams, these meteorites sampled isotopically and chemically homogeneous nebular reservoirs. The linear correlation of 55Mn/52Cr with ε53Cr in bulk rocks likely was caused by variable fractionation of Mn/Cr, subsequent mixing of phases in nebular domains, and radiogenic ingrowth of 53Cr.

¹Kared, R.,²Moine, B.N.,¹Seddiki, A.,²Cottin, J.Y.,³Greenwood, R.C.,³Franchi, I.A.
Arabian Journal of Earth Sciences 12, 442 Link to Article [DOI: 10.1007/s12517-019-4604-9]
¹Laboratoire Géoressources et Risques Naturels (GEOREN); Oran2 University, BP: 1510, Oran, 31000, Algeria
²Magmas & Volcanoes Laboratory UMR6524 CNRS, Lyon University, UJM, Saint-Etienne, France
³Planetary and Space Sciences, Department of Physical Sciences, The Open University, Walton Hall, Milton Keynes, MK7 6AA, United Kingdom

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¹E. V. Petrova,¹V. I. Grokhovsky,²T. Kohout,¹R. F. Muftakhetdinova,¹G. A. Yakovlev
Geochemistry International 57, 923-930 Link to Article [DOI https://doi.org/10.1134/S0016702919080081]
¹Ural Federal University, Institute of Physics and Technology, Yekaterinburg, Russia
²University of Helsinki, Faculty of Science, Helsinki, Finland

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¹C.Lorenz,¹M.Ivanova,²A.Krot,³V.Shuvalov
Geochemistry (Chemie der Erde) (In Press) Link to Article [https://doi.org/10.1016/j.chemer.2019.07.005]
¹Vernadsky Institute of Geochemistry and Analytical Chemistry, Russian Academy of Sciences, Kosygin St. 19, Moscow, 119991, Russia
²University of Hawai‘i at Mānoa, 1680 East-West Road, Honolulu, HI, 96822, USA
³Institute for Dynamics of Geosphere, Russian Academy of Sciences, Moscow, Russia
Copyright Elsevier

Calcium-aluminum-rich inclusions (CAIs) are the oldest Solar System solids dated that formed by evaporation, condensation, aggregation and, sometimes, melting processes near the protoSun, and were subsequently dispersed throughout the protoplanetary disk by still poorly-understood mechanism(s). Here we report on the discovery of disk- and bowl-shaped centimeter-sized igneous CAIs in CV (Vigarano type) carbonaceous chondrites. Igneous CAIs of these shapes are not expected for crystallization of melt droplets in a low gravity field of the protoplanetary disk. We have tested several models for the formation of disk- and bowl-shaped igneous CAIs including: collision, aerodynamic deformation and shock flattening. We conclude that these CAIs resulted from aerodynamic deformation of CAI-like melt droplets and propose the following multistage formation scenario: (1) nearly complete melting and acceleration of CAIs at <30 km/s in the CAI-forming region having approximately solar dust/gas ratio; (2) aerodynamic deformation, ablation, deceleration, solidification at ˜30–40 K/min, Wark-Lovering rims formation, and deceleration of the CAIs entering a dust-rich inner disk wall; (3) radial drift of the solidified deformed CAIs towards the Sun; (4) heating and partial melting of the deformed CAIs by solar radiation that preserve their morphology; (5) cooling and crystallization of CAIs at ˜2 K/h; (5) radial transport of CAIs from their formation region to the outer disk.

^1,2,3Alexander N.Krot,¹Kazuhide Nagashima,⁴Steven B.Simon,⁵Chi Ma,⁶Harold C.Connolly Jr.,¹Gary R.Huss,^7,8,9Andrew M.Davis,³MartinBizzarro
Geochemistry (Chemie der Erde)(In Press) Link to Article [https://doi.org/10.1016/j.chemer.2019.08.001]
¹School of Ocean, Earth Science and Technology, Hawai‘i Institute of Geophysics and Planetology, University of Hawai‘i at Mānoa, USA
²Geoscience Institute/Mineralogy, Goethe University Frankfurt, Germany
³Centre for Star and Planet Formation, University of Copenhagen, Denmark
⁴Institute of Meteoritics, University of New Mexico, USA
⁵Division of Geological and Planetary Sciences, California Institute of Technology, USA
⁶Department of Geology, School of Earth and Environment, Rowan University, USA
⁷Department of the Geophysical Sciences, The University of Chicago, USA
⁸Enrico Fermi Institute, The University of Chicago, USA
⁹Chicago Center for Cosmochemistry, USA
Copyright Elsevier

Grossite (CaAl₄O₇) is one of the one of the first minerals predicted to condense from a gas of solar composition, and therefore could have recorded isotopic compositions of reservoirs during the earliest stages of the Solar System evolution. Grossite-bearing Ca,Al-rich inclusions (CAIs) are a relatively rare type of refractory inclusions in most carbonaceous chondrite groups, except CHs, where they are dominant. We report new and summarize the existing data on the mineralogy, petrography, oxygen and aluminum-magnesium isotope systematics of grossite-bearing CAIs from the CR, CH, CB, CM, CO, and CV carbonaceous chondrites. Grossite-bearing CAIs from unmetamorphosed (petrologic type 2―3.0) carbonaceous chondrites preserved evidence for heterogeneous distribution of ²⁶Al in the protoplanetary disk. The inferred initial ²⁶Al/²⁷Al ratio [(²⁶Al/²⁷Al)₀] in grossite-bearing CAIs is generally bimodal, ˜0 and ˜5×10^‒5; the intermediate values are rare. CH and CB chondrites are the only groups where vast majority of grossite-bearing CAIs lacks resolvable excess of radiogenic ²⁶Mg. Grossite-bearing CAIs with approximately the canonical (²⁶Al/²⁷Al)₀ of ˜5×10^‒5 are dominant in other chondrite groups. Most grossite-bearing CAIs in type 2‒3.0 carbonaceous chondrites have uniform solar-like O-isotope compositions (Δ¹⁷O ˜ ‒24±2‰). Grossite-bearing CAIs surrounded by Wark-Lovering rims in CH chondrites are also isotopically uniform, but show a large range of Δ¹⁷O, from ˜ ‒40‰ to ˜ ‒5‰, suggesting an early generation of gaseous reservoirs with different oxygen-isotope compositions in the protoplanetary disk. Igneous grossite-bearing CAIs surrounded by igneous rims of ±melilite, Al-diopside, and Ca-rich forsterite, found only in CB and CH chondrites, have uniform ¹⁶O-depleted compositions (Δ¹⁷O ˜ ‒14‰ to ‒5‰). These CAIs appear to have experienced complete melting and incomplete O-isotope exchange with a ¹⁶O-poor (Δ¹⁷O ˜ ‒2‰) gas in the CB impact plume generated about 5 Ma after CV CAIs. Grossite-bearing CAIs in metamorphosed (petrologic type >3.0) CO and CV chondrites have heterogeneous Δ¹⁷O resulted from mineralogically-controlled isotope exchange with a ¹⁶O-poor (Δ¹⁷O ˜ ‒2 to 0‰) aqueous fluid on the CO and CV parent asteroids 3‒5 Ma after CV CAIs. This exchange affected grossite, krotite, melilite, and perovskite; corundum, hibonite, spinel, diopside, forsterite, and enstatite preserved their initial O-isotope compositions. The internal ²⁶Al-²⁶Mg isochrons in grossite-bearing CAIs from weakly-metamorphosed CO and CV chondrites were not disturbed during this oxygen-isotope exchange.

HCCJr is grateful to Klaus Keil for all his sound profession counsel and collegial friendship over the years. He has always been willing to talk and has the generous nature of listening and sharing his thoughts freely and constructively. Professor Klaus Keil has been a mentor to and played a key role in the careers of three of the authors of this paper (ANK, KN, and GRH). He has also influenced the careers of the other authors and most of the people who have worked on meteorites over the past 50+ years. We therefore dedicate this paper to Professor Keil and present it in this Special Issue of Geochemistry.

^1,2A.N.Krot,²C.Ma,¹K.Nagashima,^4,5,6A.M.Davis,³J.R.Beckett,⁷S.B.Simon,⁸M.Komatsu,⁹T.J.Fagan,²F.Brenker,¹⁰M.A.Ivanova,¹¹A.Bischoff
Geochemistry (Chemie der Erde) (in Press) Link to Article [https://doi.org/10.1016/j.chemer.2019.07.001]
¹Hawai‘i Institute of Geophysics and Planetology, School of Ocean and Earth Science and Technology, University of Hawai‘i at Mānoa, 1680 East-West Road, Honolulu, HI 96822, USA
²Geoscience Institute, Goethe University, 60438 Frankfurt am Main, Germany
³Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena CA 91125, USA
⁴Department of the Geophysical Sciences, The University of Chicago, Chicago, IL 60637, USA
⁵Enrico Fermi Institute, The University of Chicago, Chicago, IL 60637, USA
⁶Chicago Center for Cosmochemistry, Chicago, IL 60637, USA
⁷Institute of Meteoritics, University of New Mexico, Albuquerque, NM 87131, USA
⁸The Graduate University for Advanced Studies (SOKENDAI), Hayama, Kanagawa 240-0193 Japan
⁹Earth Sciences Department, Waseda University, Shinjuku-ku, Tokyo 169-8050, Japan
¹⁰Vernadsky Institute of Geochemistry of Russian Academy of Sciences, Kosygin St. 19, Moscow 119991, Russia
¹¹Institut für Planetologie, University of Münster, Wilhelm-Klemm-Str. 10, 48149 Münster, Germany
Copyright Elsevier

We report on the mineralogy, petrography, and in situ oxygen isotopic composition of twenty-five ultrarefractory calcium-aluminum-rich inclusions (UR CAIs) in CM2, CR2, CH3.0, CV3.1―3.6, CO3.0―3.6, MAC 88107 (CO3.1-like), and Acfer 094 (C3.0 ungrouped) carbonaceous chondrites. The UR CAIs studied are typically small, < 100 µm in size, and contain, sometimes dominated by, Zr-, Sc-, and Y-rich minerals, including allendeite (Sc4Zr3O12), and an unnamed ((Ti,Mg,Sc,Al)3O5) mineral, davisite (CaScAlSiO6), eringaite (Ca3(Sc,Y,Ti)2Si3O12), kangite ((Sc,Ti,Al,Zr,Mg,Ca,□)2O3), lakargiite (CaZrO3), warkite (Ca2Sc6Al6O20), panguite ((Ti,Al,Sc,Mg,Zr,Ca)1.8O3), Y-rich perovskite ((Ca,Y)TiO3), tazheranite ((Zr,Ti,Ca)O2―x), thortveitite (Sc2Si2O7), zirconolite (orthorhombic CaZrTi2O7), and zirkelite (cubic CaZrTi2O7). These minerals are often associated with 50―200 nm-sized nuggets of platinum group elements. The UR CAIs occur as: (i) individual irregularly-shaped, nodular-like inclusions; (ii) constituents of unmelted refractory inclusions – amoeboid olivine aggregates (AOAs) and Fluffy Type A CAIs; (iii) relict inclusions in coarse-grained igneous CAIs (forsterite-bearing Type Bs and compact Type As); and (iv) relict inclusions in chondrules. Most UR CAIs, except for relict inclusions, are surrounded by single or multilayered Wark-Lovering rims composed of Sc-rich clinopyroxene, ±eringaite, Al-diopside, and ±forsterite. Most of UR CAIs in carbonaceous chondrites of petrologic types 2―3.0 are uniformly 16O-rich (Δ17O ˜ ―23‰), except for one CH UR CAI, which is uniformly 16O-depleted (Δ 17O ˜ ―5‰). Two UR CAIs in Murchison have heterogeneous Δ17O. These include: an intergrowth of corundum (˜ ‒24‰) and (Ti,Mg,Sc,Al)3O5 (˜ 0‰), and a thortveitite-bearing CAI (˜ ‒20 to ˜ ‒5‰); the latter apparently experienced incomplete melting during chondrule formation. In contrast, most UR CAIs in metamorphosed chondrites are isotopically heterogeneous (Δ17O ranges from ˜ ―23‰ to ˜ ―2‰), with Zr- and Sc-rich oxides and silicates, melilite and perovskite being 16O-depleted to various degrees relative to uniformly 16O-rich (Δ17O ˜ ―23‰) hibonite, spinel, Al-diopside, and forsterite. We conclude that UR CAIs formed by evaporation/condensation, aggregation and, in some cases, melting processes in a 16O-rich gas of approximately solar composition in the CAI-forming region(s), most likely near the protoSun, and were subsequently dispersed throughout the protoplanetary disk. One of the CH UR CAIs formed in an 16O-depleted gaseous reservoir providing an evidence for large variations in Δ17O of the nebular gas in the CH CAIs-forming region. Subsequently some UR CAIs experienced oxygen isotopic exchange during melting in 16O-depleted regions of the disk, most likely during the epoch of chondrule formation. In addition, UR CAIs in metamorphosed CO and CV chondrites, and, possibly, the corundum-(Ti,Mg,Sc,Al)3O5 intergrowth in Murchison experienced O-isotope exchange with aqueous fluids on the CO, CV, and CM chondrite parent asteroids. Thus, both nebular and planetary exchange with 16O-depleted reservoirs occurred.

¹Nadia Vogel,^1,2Veronika S.Heber,³Peter Bochsler,⁴Donald S.Burnett,¹Colin Maden,¹Rainer Wieler
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2019.08.007]
¹ETH Zürich, Institute for Geochemistry and Petrology, Department of Earth Sciences, Clausiusstrasse 25, CH-8092 Zürich, Switzerland
²Department of Earth and Space Sciences, University of California, Los Angeles, CA 90095-1567, USA
³Physikalisches Institut, University of Bern, Sidlerstrasse 5, CH-3012 Bern, Switzerland
⁴California Institute of Technology, Division of Geological and Planetary Sciences, Pasadena, CA 91125, USA
Copyright Elsevier

We discuss elemental abundances of noble gases in targets exposed to the solar wind (SW) onboard the “Genesis” mission during the three different SW “regimes”: “Slow” (interstream, IS) wind, “Fast” (coronal hole, CH) wind and solar wind related to coronal mass ejections (CME). To this end we first present new Ar, Kr, and Xe elemental abundance data in Si targets sampling the different regimes. We also discuss He, Ne, and Ar elemental and isotopic abundances obtained on Genesis regime targets partly published previously. Average Kr/Ar ratios for all three regimes are identical to each other within their uncertainties of about 1% with one exception: the Fast SW has a 12% lower Xe/Ar ratio than do the other two regimes. In contrast, the He/Ar and Ne/Ar ratios in the CME targets are higher by more than 20% and 10%, respectively, than the corresponding Fast and Slow SW values, which among themselves vary by no more than 2-4%.
Earlier observations on lunar samples and Genesis targets sampling bulk SW wind had shown that Xe, with a first ionisation potential (FIP) of ∼12 eV, is enriched by about a factor of two in the bulk solar wind over Ar and Kr compared to photospheric abundances, similar to many “low FIP” elements with a FIP less than ∼10 eV. This behaviour of the “high FIP” element Xe was not easily explained, also because it has a Coulomb drag factor suggesting a relatively inefficient feeding into the SW acceleration region and hence a depletion relative to other high FIP elements such as Kr and Ar. The about 12% lower enrichment of Xe in Genesis’ Fast SW regime observed here is, however, in line with the hypothesis that the depletion of Xe in the SW due to the Coulomb drag effect is overcompensated as a result of the relatively short ionisation time of Xe in the ion-neutral separation region in the solar chromosphere. We will also discuss the rather surprising fact that He and Ne in CME targets are quite substantially enriched (by 20% and 10%, respectively) relative to the other solar wind regimes, but that this enrichment is not accompanied by an isotopic fractionation. The Ne isotopic data in CMEs are consistent with a previous hypothesis that isotopic fractionation in the solar wind is mass-dependent.