¹Christopher S. Noyes,²Guy. J. Consolmagno,²Robert J. Macke,^3,4Daniel T. Britt,¹Cyril P. Opeil
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13895]
¹Department of Physics, Boston College, 140 Commonwealth Avenue, Chestnut Hill, Massachusetts, 02467 USA
²Vatican Observatory, Vatican City, V-00120 Vatican City State
³Department of Physics, University of Central Florida, 4111 Libra Dr, Orlando, Florida, 32816 USA
⁴Center of Lunar and Asteroid Surface Science, 12354 Research Pkwy, Suite 214, Orlando, Florida, 32826 USA
Published by arrangement with John Wiley & Sons

We have measured the thermal conductivity and specific heat capacity of subsamples from four iron meteorites with nickel concentrations between 5% and 8% (Agoudal, Canyon Diablo, Muonionalusta, and Sikhote-Alin) at temperatures between 5 and 300 K. From these, we have calculated their thermal diffusivity and thermal inertia values across this temperature range. For comparison, we also measured subsamples from two L chondrites (NWA 11038 and NWA 11344) at the same time, using the same methods. The thermal diffusivity results of the irons show a relatively constant value for T > 100 K with a characteristic low-temperature maxima at ∼5 K for the iron meteorites; by contrast, the diffusivities of the L chondrites fell by a factor of two over this range and reached low-temperature maxima at ∼20 K. Thermal inertia values show a crossover behavior, with a strong increase in thermal inertia as temperatures drop below 55 K and a less dramatic change at higher temperatures. Our new diffusivity and inertia values cover a wider range of temperatures than previous literature data for iron meteorites. They also provide a useful ground truth in understanding remotely sensed thermal inertias of potentially metal-rich asteroids, including 16 Psyche, target of the NASA Psyche mission.

¹Megan E.Guenther,¹Stephanie M.Brown Krein,¹Timothy L.Grove
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2022.07.023]
¹Massachusetts Institute of Technology, Department of Earth, Atmospheric and Planetary Sciences 54-1212, 77 Massachusetts Ave, Cambridge, MA 02139, United States
Copyright Elsevier

We present the results of high pressure, high temperature multiple saturation experiments at variable oxygen fugacity ( conditions (IW+1.5 and IW-2.1) on three lunar high titanium ultramafic glasses: the Apollo 17 Orange glass (A17O, 9.1 wt. % TiO2), the Apollo 15 Red glass (A15R, 13.8 wt. % TiO2), and the Apollo 14 Black glass (A14B, 16.4 wt. % TiO2). We performed experiments in graphite ( = IW+1.5) and iron ( = IW-2.1) capsules. The experimentally determined multiple saturation points (MSPs) in graphite capsules are 2.5 GPa and ∼1530℃ (A17O), 1.3 GPa and ∼1350℃ (A15R), and 1.55 GPa and ∼1425℃ (A14B). In iron, we found MSPs of 3.3 GPa and ∼1565℃ (A17O), 2.8 GPa and ∼1490℃ (A15R), and 4.0 GPa and ∼1540℃ (A14B). These results, when combined with previous experiments on the lunar ultramafic glasses, indicate that the increase in the pressure of multiple saturation is linearly proportional to the TiO2 content of the melt , R2 = 0.93, RMSE = 0.2 GPa). The high depths of melting correlated with the lowest conditions are hard to reconcile with buoyancy constraints on these iron and titanium rich magmas. In addition, measurements of on the orange glass as well as the presence of iron blebs in the glasses suggest that the glasses were reduced during eruption. To reconcile buoyancy constraints with estimates, we present a model in which the high titanium magmas experienced higher conditions at their source, but underwent subsequent reduction at shallow depths (4-52 km) just prior to their eruption. In this model, we can then further bracket the depth of melting to be from the minimum multiple saturation pressure in graphite to the deepest depth at which the magmas are buoyant: assuming the Hess and Parmentier (1995) post overturn cumulate mantle, the depths of melting range from ∼550-770 km for the A17O glass, ∼260-490 km for the A15R glass, and ∼320-350 km for the A14B glass.

^1,2A.P.Jordan,³M.L.Shusterman,⁴C.J.Tai Udovicic
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2022.115184]
¹Institute for the Study of Earth, Oceans, and Space, University of New Hampshire, Durham, NH, USA
²Solar System Exploration Research Virtual Institute, NASA Ames Research Center, Moffett Field, CA, USA
³School of Earth and Space Exploration, Arizona State University, Tempe, AZ, USA
⁴Northern Arizona University, Flagstaff, AZ, USA
Copyright Elsevier

Micrometeoroid impacts, solar wind bombardment, and dielectric breakdown driven by solar energetic particles all potentially alter the optical properties of the lunar regolith by creating submicroscopic metallic iron (smFe0), which includes both nanophase (<33nm) and microphase (>33nm) iron. We create a simple model that describes the time-dependent accumulation of optically active smFe0 in the lunar highlands. Our model synthesizes recent analyses of how space weathering processes form smFe0-bearing agglutinates and rims on soil grains and how impact gardening controls the exposure time of these grains. It successfully reproduces the results of a prior analysis of the formation of smFe0 in the highlands, particularly in regard to nanophase iron, showing that there is consistency among diverse analyses of Apollo samples and of orbital observations. We find that the results of our model are not consistent with the solar wind directly forming smFe0 (although the solar wind may play a role in optical maturation via hydrogen implantation). Our model results are consistent with smFe0 in the lunar highlands being created mainly by micrometeoroid impacts, with a possible contribution from dielectric breakdown weathering.

¹Philipp Gleißner,¹Julie Salme,¹Harry Becker
Earth and Planetary Science Letters 593, 117680 Link to Article [https://doi.org/10.1016/j.epsl.2022.117680]
¹Freie Universität Berlin, Institut für Geologische Wissenschaften, Malteserstr. 74-100, 12249 Berlin, Germany
Copyright Elsevier

Elevated water contents in various lunar materials have invigorated the discussion on the volatile content of the lunar interior and on the extent to which the volatile element inventory of lunar magmatic rocks is controlled by volatility and degassing. Abundances of moderately volatile and siderophile elements can reveal insights into lunar processes such as core formation, late accretion and volatile depletion. However, previous assessments relied on incomplete data sets and data of variable quality. Here we report mass fractions of the siderophile volatile elements Cu, Se, Ag, S, Te, Cd, In, and Tl in lunar magmatic rocks, analyzed by state-of-the-art isotope dilution-inductively coupled plasma mass spectrometry. The new data enable us to disentangle distribution processes during the formation of different magmatic rock suites and to constrain mantle source compositions. Mass fractions of Cu, S, and Se in mare basalts and magnesian suite norites clearly correlate with indicators of fractional crystallization. Similar mass fractions and fractional crystallization trends in mafic volcanic and plutonic rocks indicate that the latter elements are less prone to degassing during magma ascent and effusion than proposed previously. The latter processes predominate only for specific elements (e.g., Tl, Cd) and complementary enrichments of these elements also occur in some brecciated highland rocks. A detailed comparison of elements with different affinities to metal or sulfide and gas phase reveals systematic differences between lunar magmatic rock suites. The latter observation suggests a predominant control of the variations of S, Se, Cu, and Ag by mantle source composition instead of late-stage magmatic degassing. New estimates of mantle source compositions of two low-Ti mare basalt suites support the notion of a lunar mantle that is strongly depleted in siderophile volatile elements compared to the terrestrial mantle.

¹Mehmet Yesiltas,²Yoko Kebukawa,³Timothy D. Glotch,⁴Michael Zolensky,⁴Marc Fries,⁵Namik Aysal,⁵Fatma S. Tukel
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13893]
¹Faculty of Aeronautics and Space Sciences, Kirklareli University, Kirklareli, 39100 Turkey
²Faculty of Engineering, Yokohama National University, 240-8501 Yokohama, Japan
³Department of Geosciences, Stony Brook University, Stony Brook, New York, 11790 USA
⁴Astromaterials Research and Exploration Science, Johnson Space Center, NASA, Houston, Texas, 77058 USA
⁵Department of Geological Engineering, Istanbul University-Cerrahpasa, Istanbul, 34320 Turkey
Published by arrangement with John Wiley & Sons

Ungrouped carbonaceous chondrites are not easily classified into one of the well-established groups due to compositional/petrological differences and geochemical anomalies. Type 2 ungrouped carbonaceous chondrites represent a very small fraction of all carbonaceous chondrites. They can potentially represent different aspects of asteroids and their regolith material. By conducting a multitechnique investigation, we show that Queen Alexandra Range (QUE) 99038 and Elephant Moraine (EET) 83226 do not resemble type 2 carbonaceous chondrites. QUE 99038 exhibits coarse-grained matrix, Fe-rich rims on olivines, and an apparent lack of tochilinite, suggesting that QUE 99038 has been metamorphosed. Its polyaromatic organic matter structures closely resemble oxidized CV3 chondrites. EET 83226 exhibits a clastic texture with high porosity and shows similarities to CO3 chondrites. It consists of numerous large chondrules with fine-grained rims that are often fragmented and discontinuous and set within matrix, suggesting a formation mechanism for the rims in a regolith environment. The kind of processes that can result in such chemical compositions as in QUE 99038 and EET 83226 is currently not fully known and clearly presents a conundrum. Tarda is a highly friable carbonaceous chondrite with close resemblance to Tagish Lake (ungrouped C2 chondrite). It comprises different types of chondrules (some with Fe-rich rims), framboid magnetite, sulfides, carbonates, and phyllosilicate- and carbon-rich matrix, and is consistent with being an ungrouped C2 chondrite.

¹Steven D. Dibb,¹James F. Bell III,^1,2Laurence A. J. Garvie
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.13891]
¹School of Earth and Space Exploration, Arizona State University, Tempe, Arizona, 85287 USA
²Buseck Center for Meteorite Studies, Arizona State University, Tempe, Arizona, 85287 USA
Published by arrangement with John Wiley & Sons

The 350–2500 nm reflectance spectra of five enstatite achondrites (aubrites), five metal-rich chondrites (CBa, CBb, CH/CBb, and ungrouped), and seven sulfide mineral samples (three troilites, pyrrhotite, pentlandite, a mixture of pentlandite and chalcopyrite, and oldhamite) have been measured to search for spectral parameters that may offer insight into the surface composition of so-called “spectrally featureless” asteroids. Spectral data were acquired from powders, slabs, and hand samples. Aubrites exhibit high reflectance, generally positive slopes at visible wavelengths, and low-to-negative infrared slopes, consistent with E-/Xe-type asteroids. The metal-rich chondrites exhibit low reflectance, moderate visible slopes, and low near-infrared slopes, somewhat consistent with M−/X-complex asteroids. The metal-rich chondrites exhibit absorption features at ~900 nm arising from Fe2+-bearing silicates. Sulfides exhibit low to moderate reflectance and high visible and near-infrared slope, intermediate to the T- and L-type asteroids. The D-type asteroids, which have high visible and near-infrared slopes, are not well-matched by sulfides. Spectral data of the largest M−/X-type asteroid, (16) Psyche, are consistent with both powder from the Isheyevo CH/CBb chondrite and powder of meteoritic troilite. The data presented here will support interpretation of data returned from future spacecraft missions to “spectrally featureless” asteroids, like the Psyche, Lucy, and DART/Hera missions.

¹Keqing Zong et al. (>10)
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2022.06.037]
¹State Key Laboratory of Geological Processes and Mineral Resources, School of Earth Sciences, China University of Geosciences, Wuhan 430074, China
Copyright Elsevier

Lunar soil is a fine mixture of local rocks and exotic components. The bulk-rock chemical composition of the newly returned Chang’E-5 (CE-5) lunar soil was studied to understand its chemical homogeneity, exotic additions, and origin of landing site basalts. Concentrations of 48 major and trace elements, including many low-concentration volatile and siderophile elements, of two batches of the scooped CE-5 soil samples were simultaneously obtained by inductively coupled plasma mass spectrometry (ICP-MS) with minimal sample consumption. Their major and trace elemental compositions (except for Ni) are uniform at milligram levels (2–4 mg), matching measured compositions of basaltic glasses and estimates based on mineral modal abundances of basaltic fragments. This result indicates that the exotic highland and KREEP (K, rare earth elements, and P-rich) materials are very low (<5%) and the bulk chemical composition (except for Ni) of the CE-5 soil can be used to represent the underlying mare basalt. The elevated Ni concentrations reflect the addition of about 1 wt% meteoritic materials, which would not influence the other bulk composition except for some highly siderophile trace elements such as Ir. The CE-5 soil, which is overall the same as the underlying basalt in composition, displays low Mg# (34), high FeO (22.7 wt%), intermediate TiO2 (5.12 wt%), and high Th (5.14 µg/g) concentrations. The composition is distinct from basalts and soils returned by the Apollo and Luna missions, however, the depletion of volatile or siderophile elements such as K, Rb, Mo, and W in their mantle sources is comparable. The incompatible lithophile trace element concentrations (e.g., Ba, Rb, Th, U, Nb, Ta, Zr, Hf, and REE) of the CE-5 basalts are moderately high and their pattern mimics high-K KREEP. The pattern of these trace elements with K, Th, U, Nb, and Ta anomalies of the CE-5 basalts cannot be explained by the partial melting and crystallization of olivine, pyroxene, and plagioclase. Thus, the mantle source of the CE-5 landing site mare basalt could have contained KREEP components, likely as trapped interstitial melts. To reconcile these observations with the initial unradiogenic Sr and radiogenic Nd isotopic compositions of the CE-5 basalts, clinopyroxene characterized by low Rb/Sr and high Sm/Nd ratios could be one of the main minerals in the KREEP-bearing mantle source. Consequently, we propose that the CE-5 landing site mare basalts very likely originated from partial melting of a shallow and clinopyroxene-rich (relative to olivine and orthopyroxene) upper mantle cumulate with a small fraction (about 1–1.5 %) of KREEP-like materials.

^1,2Piers Koefoed,^1,3Olga Pravdivtseva,^1,3Ryan Ogliore,⁴Yun Jiang,^1,2Katharina Lodders,^1,2Mason Neuman,^1,2Kun Wang王昆
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2022.06.021]
¹McDonnell Center for the Space Sciences, Washington University in St. Louis, St. Louis, MO 63130, USA
²Department of Earth and Planetary Sciences, Washington University in St. Louis, St. Louis, MO 63130, USA
³Department of Physics, Washington University in St. Louis, St. Louis, MO 63130, USA
⁴CAS Key Laboratory of Planetary Sciences, Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing 210008, China
Copyright Elsevier

The many unique characteristics of CB chondrites have resulted in the impact hypothesis becoming the favoured model for their formation. Here, we further investigate the formation mechanisms of CB chondrites by analysing the elemental and K isotope compositions of chondrules and bulk fractions from the CBa chondrite Gujba. Similar to previous work, the refractory element ratios in the Gujba chondrules show evidence of a differentiated precursor, with the Nb/Ta, Zr/Hf, Sc/Th and Zr/Th ratios showing fractionation relative to other chondrites. In addition, the bulk fractions, and to a lesser extent the chondrules with attached matrix and metals, display significantly more refractory element fractionation and a large enrichment in light REEs. Based on EDS elemental mapping and comparisons with previous studies, the most likely source of this highly fractionated material appears to be the small amount of heterogeneously distributed interstitial fine-grained material within Gujba. These large refractory element fractionations (i.e., Nb/Ta, Zr/Hf, Sc/Th Zr/Th, and LREE/HREE) are best explained by a significant partial melting process such as crustal formation. Nevertheless, the mechanism of patrial melting cannot be conclusively determined with the data available here. The K isotopic compositions of the Gujba chondrules analyzed here range from −2.24‰ to −0.41‰ in δ41K, whereas the bulk analyses show δ41K values of −0.81‰ to −0.72‰. This range of chondrule K isotope compositions is significantly larger, and extends to much lighter compositions, compared to all other chondrites measured so far by bulk ICP-MS. In addition, the Gujba chondrules display a clear negative correlation of K isotopic composition with K concentration, with the chondrules showing the lightest K isotope compositions having the highest K concentrations. This distinctive correlation indicates that evaporation was likely the dominant process affecting the K isotopic variation observed in the Gujba chondrules. Nevertheless, the extremely light δ41K values seen in the most K-rich chondrules (which are lighter than any other early solar system material so far measured) indicate that incomplete condensation likely took place before evaporation. As such, we propose a two-stage model to explain the formation of chondrules in Gujba, with Stage 1 characterized by incomplete condensation of vaporized material with an average isotopic fractionation factor (α) of 0.9984 (when using the most K enriched chondrule to constrain the model), and Stage 2 representing partial evaporation in a vapor plume with an average α range of 0.9976 to 0.9990. Using these α values we calculate an approximate vapor saturation index value of 0.935 for condensation and between 0.903 and 0.960 for evaporation. This formation process requiring both condensation and evaporation for CB chondrules is consistent with an impact generated vapor plume and further expands our understanding of CB chondrite formation.

¹Eizo Nakamura et al. (>10)
Proceedings of the Japan Academy, Series B 98, 227-282 Link to Article [DOI https://doi.org/10.2183/pjab.98.015]
¹The Pheasant Memorial Laboratory for Geochemistry and Cosmochemistry, Institute for Planetary Materials, Okayama University

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¹Yuchen Xu,²Yangting Lin,²Jialong Hao,³Makoto Kimura,²Sen Hu,²Wei Yang,¹Yang Liu,¹Yongliao Zou
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2022.07.016]
¹State Key Laboratory of Space Weather, National Space Science Center, Chinese Academy of Sciences, Beijing 100190, China
²Key Laboratory of Earth and Planetary Physics, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China
³National Institute of Polar Research, Tokyo 190-8518, Japan
Copyright Elsevier

The solar system could be separated into two zones based on the isotopic dichotomy between non-carbonaceous and carbonaceous groups, with the latter likely accreted in the outer solar system. Among carbonaceous groups, the CM chondrite contains high abundances of organic carbon and water. They have undergone aqueous alteration, thermal metamorphism and brecciation to different degrees (e.g., Rubin et al., 2007; Rubin et al., 2009; Tonui et al., 2014, Zolensky et al., 1997), which contributed to erasing most of the solar nebular records. Asuka 12169 was reported as the most primitive CM chondrite based on petrological and geochemical results, with little aqueous alteration (Kimura et al., 2020). In this paper, we report a survey of presolar grains in the fine-grained matrix and the accetionary rims of chondrules and CAIs in this meteorite, based on NanoSIMS mapping of C-, O-, and Si-isotopes. A total of 158 presolar grains were identified, including 119 silicates/oxides (208±20 ppm), 38 SiC (73±12 ppm) and 1 carbonaceous grain (2+5 -2 ppm). These abundances are within the maximum abundance ranges of primitive chondrites (80-280 ppm for O-rich grains and 10-180 ppm for C-rich grains). In comparison with most CM chondrites (<40 ppm), Asuka 12169 is uniquely rich in presolar silicates (185±18 ppm), with a high presolar silicate/oxide ratio of ∼8, therefore providing robust evidence for little aqueous alteration. The high abundances of presolar SiC and silicates in Asuka 12169 clearly show its pristine properties regarding both thermal and aqueous alteration. Group 1, 2, 3 and 4 subtypes of presolar O-rich grains account for 84%, 2.5%, 0.8% and 12.6%, respectively. One O-rich grain shows a high enhancement in 17O/16O and a subsolar 18O/16O ratio (17O/16O = 6.45±0.09×10-3 and 18O/16O = 1.90±0.02×10-3), indicating a stellar origin in binary star systems or novae. Most identified presolar SiC are mainstream grains of AGB origins. One with 28Si-excess is classified as an X grain, suggesting a supernova origin. There are two SiC grains that have 12C/13C <10 but close-to-solar Si isotopic ratios, and are therefore classified as AB type. The pristine features of Asuka 12169 suggest that it was probably located in the outermost few kilometers of the CM asteroid, where temperature was high enough for sublimation of water ice under vacuum, but where no aqueous alteration occurred, and where the depth was enough for lithification. The high abundances of various types of presolar grains, together with the petrographic information of Asuka 12169, provide crucial constrains on the original properties and subsequent evolution of the CM asteroids.