Trace Element Conundrum of Natural Quasicrystals

1Tommasini, S.,1,2Bindi, L.,3,6Petrelli, M.,4Asimow, P.D.,5Steinhardt, P.J.
ACS Earth and Space Chemistry (in Press) Link to Article [DOI: 10.1021/acsearthspacechem.1c00004]
1Dipartimento di Scienze della Terra, Università Degli Studi di Firenze, Via La Pira 4, Firenze, I-50121, Italy
2CNR-Istituto di Geoscienze e Georisorse, Sezione di Firenze, Via La Pira 4, Firenze, I-50121, Italy
3Dipartimento di Fisica e Geologia, Università Degli Studi di Perugia, Perugia, I-06123, Italy
4Division of Geological and Planetary Sciences, California Institute of Technology, 1200 E. California Blvd. M/C 170-25, Pasadena, CA 91125, United States
5Department of Physics, Princeton University, Jadwin Hall, Princeton, NJ 08544, United States
6INFN, Section of Perugia, Perugia, I-06123, Italy

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Potassium isotopic composition of various samples using a dual-path collision cell-capable multiple-collector inductively coupled plasma mass spectrometer, Nu instruments Sapphire

1Moynier, F.,1Hu, Y.,2Wang, K.,3Zhao, Y.,3Gérard, Y.,1Deng, Z.,1Moureau, J.,4Li, W.,5Simon, J.I.,6Teng, F.-Z.
Chemical Geology 571, 120144 Link to Article [DOI: 10.1016/j.chemgeo.2021.120144]
1Université de Paris, Institut de Physique du Globe de Paris, CNRS, 1 rue Jussieu, Paris, 75005, France
2Department of Earth and Planetary Sciences, Washington University in St. Louis, St Louis, MO 63130, United States
3Nu Instruments, Unit 74 Clywedog Road South Wrexham Industrial Estate, Wrexham, LL13 9X, United Kingdom
4School of Earth Sciences, Nanjing University, Nanjing, China
5Center for Isotope Cosmochemistry and Geochronology, Astromaterials Research and Exploration Science division, NASA Johnson Space Center, Houston, TX 770058, United States
6Isotope Laboratory, Department of Earth and Space Sciences, University of Washington, Seattle, WA 98195, United States

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Bennu’s global surface and two candidate sample sites characterized by spectral clustering of OSIRIS-REx multispectral images

1,2J.L.Rizos et al. (>10)
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2021.114467]
1Instituto de Astrofísica de Canarias, C/Vía Láctea s/n, E-38205 La Laguna, Tenerife, Spain
2Departamento de Astrofísica, Universidad de La Laguna, E-38206 La Laguna, Tenerife, Spain
Copyright Elsevier

The OSIRIS-REx spacecraft encountered the asteroid (101955) Bennu on December 3, 2018, and has since acquired extensive data from the payload of scientific instruments on board. In 2019, the OSIRIS-REx team selected primary and backup sample collection sites, called Nightingale and Osprey, respectively. On October 20, 2020, OSIRIS-REx successfully collected material from Nightingale. In this work, we apply an unsupervised machine learning classification through the K-Means algorithm to spectrophotometrically characterize the surface of Bennu, and in particular Nightingale and Osprey. We first analyze a global mosaic of Bennu, from which we find four clusters scattered across the surface, reduced to three when we normalize the images at 550 nm. The three spectral clusters are associated with boulders and show significant differences in spectral slope and UV value. We do not see evidence of latitudinal non-uniformity, which suggests that Bennu’s surface is well-mixed. In our higher-resolution analysis of the primary and backup sample sites, we find three representative normalized clusters, confirming an inverse correlation between reflectance and spectral slope (the darkest areas being the reddest ones) and between b’ normalized reflectance and slope. Nightingale and Osprey are redder than the global surface of Bennu by more than 1σ from average, consistent with previous findings, with Nightingale being the reddest (S′ = (−0.3 ± 1.0) × 10−3% per thousand angstroms). We see hints of a weak absorption band at 550 nm at the candidate sample sites and globally, which lends support to the proposed presence of magnetite on Bennu.

Aqueous alteration without initial water: possibility of organic-induced hydration of anhydrous silicates in meteorite parent bodies

1Hirakawa, N.,1Kebukawa, Y.,2Furukawa, Y.,3Kondo, M.,4Nakano, H.,1Kobayashi, K.
Earth, Planets and Space 73, 16 Link to Article [DOI: 10.1186/s40623-020-01352-6]
1Graduate School of Engineering Science, Yokohama National University, 79-5 Tokiwadai, Hodogaya-ku, Yokohama, 240-8501, Japan
2Department of Earth Science, Tohoku University, 6-3 Aza-aoba, Aramaki, Aoba-ku, Sendai, 980-8578, Japan
3Instrumental Analysis Center, Yokohama National University, 79-5 Tokiwadai, Hodogaya-ku, Yokohama, 240-8501, Japan
4Faculty of Culture and Sport Policy, Toin University of Yokohama, 1614 Kurogane-cho, Aoba-ku, Yokohama, 225-8503, Japan

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Noble gases in cluster chondrite clasts and their host breccias

1Kim Müsing,1Henner Busemann,1Liliane Huber,1Colin Maden,1My E. I. Riebe,1Rainer Wieler,2Knut Metzler
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13644]
1Department of Earth Sciences, Institute of Geochemistry and Petrology, ETH Zürich, Clausiusstrasse 25, CH‐8092 Zürich, Switzerland
2Institut für Planetologie, University of Münster, Wilhelm‐Klemm‐Str. 10, 48149 Münster, Germany
Copyright Elsevier

We measured noble gases in “cluster chondrite clasts” from nine unequilibrated ordinary chondrites (UOCs). For five meteorites, we also present data for so‐called “clastic matrix,” the impact‐brecciated material in which the angular to subrounded cluster chondrite clasts are often embedded. Cluster chondrite clasts are characterized by close‐fit texture of deformed and indented chondrules with lower amounts of fine‐grained interchondrule matrix than in other UOCs (Metzler 2012). They are ubiquitous in UOCs and may indicate accretion and compaction of hot and deformable chondrules within hours or days after formation. Clastic matrix of four of the five meteorites contains He and Ne implanted by the solar wind (SW), indicating that they are regolith breccias. In contrast, cluster chondrite clasts are essentially devoid of SW, confirming that they are fragments of “primary accretionary rocks” (Metzler 2012). Trapped Kr and Xe in all samples are essentially primordial (type “Q”). Trapped Xe concentrations in cluster chondrite clasts are similar to values in other UOCs of similar metamorphic grade despite their low fractions of primordial gas‐bearing fine‐grained materials. This possibly indicates that the interchondrule matrix in cluster chondrite clasts is more pristine than matrix of regular UOCs. Later loss of primordial gases during parent body metamorphism is mirrored in the decreasing concentrations of primordial noble gases with increasing petrologic type. Relative to cluster chondrite lithologies, clastic matrix often contains excesses of cosmogenic noble gases, most likely due to precompaction exposure in the parent body regolith.

Thermal metamorphism of CM chondrites: A dehydroxylation‐based peak‐temperature thermometer and implications for sample return from asteroids Ryugu and Bennu

1,2Michael A. Velbel,3Michael E. Zolensky
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13636]
1Department of Earth and Environmental Sciences, Michigan State University, 288 Farm Lane, Room 207, Natural Sciences Building, East Lansing, Michigan, 48824–1115 USA
2Division of Meteorites, Department of Mineral Sciences, National Museum of Natural History, Smithsonian Institution, Washington, District of Columbia, 20013–7012 USA
3X12 Astromaterials Research and Exploration Science, NASA Johnson Space Center, Houston, Texas, 77058 USA
Published by arrangement with John Wiley & Sons

The target bodies of C‐complex asteroid sample return missions are carbonaceous chondrite‐like near‐Earth asteroids (NEAs), chosen for the abundance and scientific importance of their organic compounds and “hydrous” (including hydroxylated) minerals, such as serpentine‐group phyllosilicates. Science objectives include returning samples of pristine carbonaceous regolith from asteroids for study of the nature, history, and distribution of its constituent minerals, organic material, and other volatiles. Heating after the natural aqueous alteration that formed the abundant phyllosilicates in CM and similar carbonaceous chondrites dehydroxylated them and altered or decomposed other volumetrically minor constituents (e.g., carbonates, sulfides, organic molecules; Tonui et al. 2003, 2014). We propose a peak‐temperature thermometer based on dehydroxylation as measured by analytical totals from electron probe microanalysis (EPMA) of matrices in a number of heated and aqueously altered (but not further heated) CM chondrites. Some CM lithologies in Maribo and Sutter’s Mill do not exhibit the matrix dehydroxylation expected for surface temperatures expected from insolation of meteoroids with their known orbital perihelia. This suggests that insolated‐heated meteoroid surfaces were lost by ablation during passage through Earth’s atmosphere, and that insolation‐heated material is more likely to be encountered among returned asteroid regolith samples than in meteorites. More generally, several published lines of evidence suggest that episodic heating of some CM material, most likely by impacts, continued intermittently and locally up to billions of years after assembly and early heating of ancestral CM chondrite bodies. Mission spectroscopic measures of hydration can be used to estimate the extent of dehydroxylation, and the new dehydroxylation thermometer can be used directly to select fragments of returned samples most likely to contain less thermally altered inventories of primitive organic molecules.

Tidal pull of the Earth strips the proto-Moon of its volatiles

1Sébastien Charnoz,2Paolo A.Sossi,3Yueh-Ning Lee,1Julien Siebert,4Ryuki Hyodo,1Laetitia Allibert,1Francesco C.Pignatale,1Maylis Landeau,5Apurva V.Oza,1Frédéric Moynier
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2021.114451]
1Université de Paris, Institut de Physique du Globe de Paris, CNRS, F-75005 Paris, France
2Institute of Geochemistry and Petrology, ETH Zürich, CH-8092 Zürich, Switzerland
3Department of Earth Sciences, National Taiwan Normal University, 88, Sec. 4, Ting-Chou Road, Taipei City 11677, Taiwan
4ISAS, JAXA, Sagamihara, Japan
5Physikalisches Institut, Universität Bern, Bern, Switzerland
Copyright Elsevier

Prevailing models for the formation of the Moon invoke a giant impact between a planetary embryo and the proto-Earth (Canup, 2004; Ćuk et al., 2016). Despite similarities in the isotopic and chemical abundances of refractory elements compared to Earth’s mantle, the Moon is depleted in volatiles (Wolf and Anders, 1980). Current models favour devolatilisation via incomplete condensation of the proto-Moon in an Earth-Moon debris-disk (Charnoz and Michaut, 2015; Canup et al., 2015; Lock et al., 2018). However the physics of this protolunar disk is poorly understood and thermal escape of gas is inhibited by the Earth’s strong gravitational field (Nakajima and Stevenson, 2014). Here we investigate a simple process, wherein the Earth’s tidal pull promotes intense hydrodynamic escape from the liquid surface of a molten proto-Moon assembling at 3–6 Earth radii. Such tidally-driven atmospheric escape persisting for less than 1 Kyr at temperatures ∼1600 − 1700 K reproduces the measured lunar depletion in K and Na, assuming the escape starts just above the liquid surface. These results are also in accord with timescales for the rapid solidification of a plagioclase lid at the surface of a lunar magma ocean (Elkins-Tanton et al., 2011). We find that hydrodynamic escape, both in an adiabatic or isothermal regime, with or without condensation, induces advective transport of gas away from the lunar surface, causing a decrease in the partial pressures of gas species (Ps) with respect to their equilibrium values (Psat). The observed enrichment in heavy stable isotopes of Zn and K (Paniello et al., 2012; Wang and Jacobsen, 2016) constrain Ps/Psat > 0.99, favouring a scenario in which volatile loss occurred at low hydrodynamic wind velocities (<1% of the sound velocity) and thus low temperatures. We conclude that tidally-driven atmospheric escape is an unavoidable consequence of the Moon’s assembly under the gravitational influence of the Earth, and provides new pathways toward understanding lunar formation.