¹Hope A.Tornabene,¹Connor D.Hilton,¹Katherine R.Bermingham,¹Richard D.Ash,¹Richard J.Walker
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2020.07.036]
¹Department of Geology, University of Maryland, College Park, Maryland, 20742, USA
Copyright Elsevie

The eight iron meteorites currently classified as belonging to the IIC group were characterized with respect to the compositions of 21 siderophile elements. Several of these meteorites were also characterized for mass independent isotopic compositions of Mo, Ru and W. Chemical and isotopic data for one, Wiley, indicate that it is not a IIC iron meteorite and should be reclassified as ungrouped. The remaining seven IIC iron meteorites exhibit broadly similar bulk chemical and isotopic characteristics, consistent with an origin from a common parent body. Variations in highly siderophile element (HSE) abundances among the members of the group can be well accounted for by a fractional crystallization model with all the meteorites crystallizing between ∼10 and ∼26% of the original melt, assuming initial S and P concentrations of 8 wt.% and 2 wt.%, respectively. Abundances of HSE estimated for the parental melt suggest a composition with chondritic relative abundances of HSE ∼6 times higher than in bulk carbonaceous chondrites, consistent with the IIC irons sampling a parent body core comprising ∼17% of the mass of the body.

Radiogenic ¹⁸²W abundances of two group IIC irons, corrected for a nucleosynthetic component, indicate a metal-silicate segregation age of 3.2 ± 0.5 Myr subsequent to the formation of Calcium-Aluminum-rich Inclusions (CAI). When this age is coupled with thermal modeling, and assumptions about the Hf/W of precursor materials, a parent body accretion age of 1.4 ± 0.5 Myr (post-CAI) is obtained.

The IIC irons and Wiley have ¹⁰⁰Ru mass independent “genetic” isotopic compositions that are identical to other irons with so-called carbonaceous chondrite (CC) type genetic affinities, but enrichments in ^94,95,97Mo and ¹⁸³W that indicate greater s-process deficits relative to most known CC iron meteorites. If the IIC irons and Wiley are of the CC type, this indicates variable s-process deficits within the CC reservoir, similar to the s-process variability within the NC reservoir observed for iron meteorites. Nucleosynthetic models indicate that Mo and ¹⁸³W s-process variability should correlate with Ru isotopic variability, which is not observed. This may indicate the IIC irons and Wiley experienced selective thermal processing of nucleosynthetic carriers, or are genetically distinct from the CC and NC precursor materials.

¹Borovička, J.,¹Spurný, P.,¹Shrbený, L.
Astronomical Journal 160, 42 Link to Article [DOI: 10.3847/1538-3881/ab9608]
¹Astronomical Institute of the Czech Academy of Sciences, Fričova 298, CZ-25165 Ondrejov, Czech Republic

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¹Busarev, V.V.,²Badyukov, D.D.,³Pronina, N.V.
Geochemistry International 58, 795-801 Link to Article [DOI: 10.1134/S0016702920070058]
¹Moscow State University (MSU), Sternberg State Astronomical Institute, Moscow, 119992, Russian Federation
²Institute of Geochemistry and Analytical Chemistry, Russian Academy of Sciences (GEOKHI RAS), ul. Kosygina 19, Moscow, 119991, Russian Federation
³Moscow State University, Geological Faculty, Moscow, 119991, Russian Federation

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^1,2Luca Bindi,³Vladimir E. Dmitrienko,⁴Paul J. Steinhardt
American Mineralogist 105, 1121-1125 Link to Article [http://www.minsocam.org/MSA/AmMin/TOC/2020/Abstracts/AM105P1121.pdf]
¹Dipartimento di Scienze della Terra, Università degli Studi di Firenze, Via La Pira 4, I-50121 Firenze, Italy
²CNR-Istituto di Geoscienze e Georisorse, Sezione di Firenze, Via La Pira 4, I-50121 Firenze, Italy
³A.V. Shubnikov Institute of Crystallography, FSRC “Crystallography and Photonics” RAS, 119333 Moscow, Russia
⁴Department of Physics, Princeton University, Jadwin Hall, Princeton, New Jersey 08544, U.S.A
Copyright: The Mineralogical Society of America

Until 2009, the only known quasicrystals were synthetic, formed in the laboratory under highly controlled conditions. Conceivably, the only quasicrystals in the Milky Way, perhaps even in the Universe, were the ones fabricated by humans, or so it seemed. Then came the report that a quasicrystal with icosahedral symmetry had been discovered inside a rock recovered from a remote stream in far eastern Russia, and later that the rock proved to be an extraterrestrial, a piece of a rare CV3 carbonaceous chondrite meteorite (known as Khatyrka) that formed 4.5 billion years ago in the pre-solar nebula. At present, the only known examples of natural quasicrystals are from the Khatyrka meteorite. Does that mean that quasicrystals must be extremely rare in the Universe? In this speculative essay, we present several reasons why the answer might be no. In fact, quasicrystals may prove to be among the most ubiquitous minerals found in the Universe.

¹Francis M. McCubbin,²Jessica J. Barnes
The American Mineralogist 105, 1270-1274 Link to Article [http://www.minsocam.org/MSA/AmMin/TOC/2020/Abstracts/AM105P1270.pdf]
¹NASA Johnson Space Center, Mailcode XI, 2101 NASA Parkway, Houston, Texas 77058, U.S.A.
²Lunar and Planetary Laboratory, University of Arizona, 1629 E University Blouvard, Tucson, Arizona 85721, U.S.A
Copyright: The Mineralogical Society of America

We conducted in situ Cl isotopic measurements of apatite within intercumulus regions and within a holocrystalline olivine-hosted melt inclusion in magnesian-suite troctolite 76535 from Apollo 17. These data were collected to place constraints on the Cl-isotopic composition of the last liquid to crystallize from the lunar magma ocean (i.e., urKREEP, named after its enrichments in incompatible lithophile trace elements like potassium, rare earth elements, and phosphorus). The apatite in the olivine-hosted melt inclusion and within the intercumulus regions of the sample yielded Cl-isotopic compositions of 28.3 ± 0.9‰ (2σ) and 30.3 ± 1.1‰ (2σ), respectively. The concordance of these values from both textural regimes we analyzed indicates that the Cl-isotopic composition of apatites in 76535 likely represents the Cl-isotopic composition of the KREEP-rich magnesian-suite magmas. Based on the age of 76535, these results imply that the KREEP reservoir attained a Cl-isotopic composition of 28–30‰ by at least 4.31 Ga, consistent
with the onset of Cl-isotopic fractionation at the time of lunar magma ocean crystallization or shortly thereafter. Moreover, lunar samples that yield Cl-isotopic compositions higher than the value for KREEP are likely affected by secondary processes such as impacts and/or magmatic degassing. The presence of KREEP-rich olivine-hosted melt inclusions within one of the most pristine and ancient KREEP-rich rocks
from the Moon provides a new opportunity to characterize the geochemistry of KREEP. In particular, a broader analysis of stable isotopic compositions of highly and moderately volatile elements could provide an unprecedented advancement in our characterization of the geochemical composition of the KREEP reservoir and of volatile-depletion processes during magma ocean crystallization, more broadly.

Marina A. Ivanova et al. (>10)
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13546]
¹Vernadsky Institute of Geochemistry and Analytical Chemistry, Moscow, 119991 Russia
Published by arrangement with John Wiley & Sons

We investigated the metal‐rich chondrite Sierra Gorda (SG) 009, a member of the new G chondrite grouplet (also including NWA 5492, GRO 95551). G chondrites contain 23% metal, very reduced silicates, and rare oxidized mineral phases (Mg‐chromite, FeO‐rich pyroxene). G chondrites are not related to CH‐CB chondrites, based on bulk O, C, and N isotopic compositions, mineralogy, and geochemistry. G chondrites have no fine‐grained matrix or matrix lumps enclosing hydrated material typical for CH‐CB chondrites. G chondrites’ average metal compositions are similar to H chondrites. Siderophile and lithophile geochemistry indicates sulfidization and fractionation of the SG 009 metal and silicates, unlike NWA 5492 and GRO 95551. The G chondrites have average O isotopic compositions Δ17O>0‰ ranging between bulk enstatite (E) and ordinary (O) chondrites. An Al‐rich chondrule from SG 009 has Δ17O>0‰ indicating some heterogeneity in oxygen isotopic composition of G chondrite components. SG 009’s bulk carbon and nitrogen isotopic compositions correspond to E and O chondrites. Neon isotopic composition reflects a mixture of cosmogenic and solar components, and cosmic ray exposure age of SG 009 is typical for O, E, and R chondrites. G chondrites are closely related to O, E, and R chondrites and may represent a unique metal‐rich parent asteroid containing primitive and fractionated material from the inner solar system. Oxidizing and reducing conditions during SG 009 formation may be connected with a chemical microenvironment and possibly could indicate that G chondrites may have formed by a planetesimal collision resulting in the lack of matrix.

^1,2James F. J. Bryson,²Benjamin P. Weiss,²Eduardo A. Lima,³Jérôme Gattacceca,⁴William S. Cassata
The Astrophysical Journal 892, 126 Link to Article [DOI
https://doi.org/10.3847/1538-4357/ab7cd4]
¹Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge CB2 3EQ, UK
²Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139, USA
³CNRS, Aix Marseille Université, IRD, Coll France, INRA, CEREGE, Aix-en-Provence, France
⁴Lawrence Livermore National Laboratory, Livermore, CA 94550, USA

Asteroid-sized bodies are predicted to have been scattered throughout the solar system following gravitational interactions with the giant planets. This process could have delivered water-rich small bodies to the inner solar system. However, evidence from the meteorite record supporting this scattering is limited due to difficulties in recovering the formation distance of meteorite parent bodies from laboratory measurements. Moreover, ancient millimeter-sized solids that formed in the inner solar system (calcium–aluminum-rich inclusions (CAIs) and chondrules) have also been proposed to have migrated throughout the solar system, which could have been key to their survival. Our understanding of the driving mechanisms, distances, and timings involved in this motion is also restricted for the same reasons. Here, we address these limitations by recovering the formation distance of the parent asteroid of the Tagish Lake meteorite from measurements of its natural remanent magnetization. We find that this meteorite experienced an ancient field intensity <0.15 μT. Accounting for the average effect of a tilted parent body rotation axis and possible uncertainties associated with the remanence acquisition mechanism, this result argues that the Tagish Lake parent body formed at >8–13 au, suggesting this body originates from the distal solar system. Tagish Lake came to Earth from the asteroid belt which, combined with our recovered formation distance, suggests that some small bodies traveled large distances throughout the solar system. Moreover, Tagish Lake contains CAIs and chondrules, indicating that these solids were capable of traveling to the distal solar system within just a few million years.

¹Gaël Rouillé,¹Cornelia Jäger,²Thomas Henning
The Astrophysical Journal 892,96 Link to Article [DOI
https://doi.org/10.3847/1538-4357/ab7a11]
¹Laboratory Astrophysics Group of the Max Planck Institute for Astronomy at the Friedrich Schiller University Jena, Institute of Solid State Physics, Helmholtzweg 3, D-07743 Jena, Germany
²Max Planck Institute for Astronomy, Königstuhl 17, D-69117 Heidelberg, Germany

The formation and growth of refractory matter on pre-existing interstellar dust grain surfaces was studied experimentally by annealing neon-ice matrices in which potential precursors of silicate grains (Mg and Fe atoms, SiO and SiO₂ molecules) and of solid carbon (C _n molecules, n = 2–10) were initially isolated. Other molecules, mainly O₃, CO, CO₂, C₃O, and H₂O, were embedded at the same time in the matrices. The annealing procedure caused the cold dopants to diffuse and interact in the neon ice. Monitoring the procedure in situ with infrared spectroscopy revealed the disappearance of the silicon oxide and carbon molecules at temperatures lower than 13 K, and the rise of the Si–O stretching band of silicates. Ex situ electron microscopy confirmed the formation of silicate grains and showed that their structure was amorphous. It also showed that amorphous carbon matter was formed simultaneously next to the silicate grains, the two materials being chemically separated. The results of the experiments support the hypothesis that grains of complex silicates and of carbonaceous materials are reformed in the cold interstellar medium, as suggested by astronomical observations and evolution models of cosmic dust masses. Moreover, they show that the potential precursors of one material do not combine with those of the other at cryogenic temperatures, providing us with a clue as to the separation of silicates and carbon in interstellar grains.

¹Joás Zapata,¹Rodrigo Negreiros
The Astrophysical Journal 892, 67 Link to Article [DOI
https://doi.org/10.3847/1538-4357/ab77b7]
¹Instituto de Física, Universidade Federal Fluminense, Av. Gal. Milton Tavares S/N, Niterói, Brazil

In this paper we consider the possibility that strange quark matter (SQM) may manifest in the form of strangelet crystal planets. These planet-like objects are made up of nuggets of SQM, organized in a crystalline structure. We consider the so-called strange matter hypothesis proposed by Bodmer, Witten, and Terazawa, in that SQM may be the absolutely stable state of matter. In this context, we analyze planets made up entirely of strangelets arranged in a crystal lattice. Furthermore, we propose that a solar system with a host compact star may be orbited by strange crystal planets. Under this assumption we calculate the relevant quantities that could potentially be observable, such as the planetary tidal disruption radius, and the gravitational-wave signals that may arise from potential star–planet merger events. Our results show that strangelet crystal planets could potentially be used as an indicator for the existence of SQM.

¹Paul S.Szabo et al. (>10)
The Astrophysical Jounal 891, 100 Link to Article [DOI
https://doi.org/10.3847/1538-4357/ab7008]
¹Institute of Applied Physics, TU Wien, Wiedner Hauptstraße 8-10, A-1040 Vienna, Austria

Pyroxenes ((Ca, Mg, Fe, Mn)₂Si₂O₆) belong to the most abundant rock forming minerals that make up the surface of rocky planets and moons. Therefore, sputtering of pyroxenes by solar wind ions has to be considered as a very important process for modifying the surface of planetary bodies. This is increased due to potential sputtering by multiply charged ions; to quantify this effect, sputtering of wollastonite (CaSiO₃) by He²⁺ ions was investigated. Thin films of CaSiO₃ deposited on a quartz crystal microbalance were irradiated, allowing precise, in situ, real time sputtering yield measurements. Experimental results were compared with SDTrimSP simulations, which were improved by adapting the used input parameters. On freshly prepared surfaces, He²⁺ ions show a significant increase in sputtering, as compared to equally fast He⁺ ions. However, the yield decreases exponentially with fluence, reaching a lower steady state after sputtering of the first few monolayers. Experiments using Ar⁸⁺ ions show a similar behavior, which is qualitatively explained by a preferential depletion of surface oxygen due to potential sputtering. A corresponding quantitative model is applied, and the observed potential sputtering behaviors of both He and Ar are reproduced very well. The results of these calculations support the assumption that mainly O atoms are affected by potential sputtering. Based on our findings, we discuss the importance of potential sputtering for the solar wind eroding the lunar surface. Estimated concentration changes and sputtering yields are both in line with previous modeling for other materials, allowing a consistent perspective on the effects of solar wind potential sputtering.