^aJay Goguen, ^bAndrew Sharits, ^cAnn Chiaramonti, ^dThomas Lafarge, ^cEdward Garboczi
Icarus (in Press) Open Access
Link to Article [https://doi.org/10.1016/j.icarus.2024.116166]
^aSpace Science Institute, 4765 Walnut St STE B, Boulder, CO 80301, United States of America
^bUES, Inc. and Materials and Manufacturing Directorate, Air Force Research Laboratory, Wright-Patterson Air Force B, Fairborn, OH, United States of America
^cApplied Chemicals and Materials Division, National Institute of Standards and Technology, Boulder, CO 80305, United States of America
^dStatistical Engineering Division, National Institute of Standards and Technology, Gaithersburg, MD 20899, United States of America

Samples of soils collected by the Apollo 11 mission (10084,2036) and the Apollo 14 mission (14163,940) were obtained from the NASA Curation and Analysis Planning Team for Extraterrestrial Materials (CAPTEM) program. The particle size, shape, and internal porosity were characterized in three dimensions (3D) using a combination of X-ray computed tomography (XCT) and mathematical analysis, with various size and shape parameters measured and calculated for each particle. High-resolution scanning electron microscopy (SEM) was used to image the particles that were too small for the two XCT instruments used. Similar characterization was carried out on samples of JSC-1A lunar soil simulant, updating a previous analysis. Approximately 14,000 lunar regolith particles and 128,000 JSC1-A particles, covering a wide range of size and shape, were characterized for this paper and the results stored in a publicly accessible database. This large number of particles enabled, for the first time, statistically valid particle shape distributions to be generated. The 3D shape distributions of the two regoliths and JSC-1A were quantitatively compared and it was found that the way particle shape and porosity depended on particle size was different between regolith and simulant. The measured size distribution of particles in the lunar soils was applied to estimate the relative contributions of different sizes to the ensemble average particle single scattering albedo and phase function. By linking our particle counts to published sieve weight fractions for the lunar samples, we find that ~80% of the total cross-section area is contributed by particles <20 μm diameter and ~ 50% by particles <8 μm diameter. The orientation-averaged two-dimensional projected areas of the actual regolith particles were computed so that this estimate was also based on real particle shapes. Such small sizes dominating the total cross-section area suggest that calculations of the elements of the scattering matrix for individual particles may be possible with modest computing capabilities leading to the development of improved models for the quantitative interpretation of remote sensing spectrophotometry and polarimetry. This 3D characterization and database will enable other computational work to be done with real lunar regolith particle shapes, including discrete element method mechanical modeling, packing simulations, further light scattering calculations, dust contamination modeling, and modeling of lunar rover interactions with collected and packed regolith particles.

^a,bYogita Kadlag, ^c,dAryavart Anand, ^eMario Fischer-Gödde, ^dKlaus Mezger, ^fKristoffer Szilas, ^gSteven Goderis, ^bIngo Leya
Icarus (in Press) Open Access
Link to Article [https://doi.org/10.1016/j.icarus.2024.116143]
^aGeosciences Division, Physical Research Laboratory, Navrangpura, Ahmedabad, Gujarat 380009, India
^bSpace Science and Planetology, Physics Institute, Universität Bern, Sidlerstrasse 5, 3012 Bern, Switzerland
^cMax-Planck-Institut für Sonnensystemforschung, Justus-von-Liebig-Weg 3, 37077 Göttingen, Germany
^dInstitut für Geologie, Universität Bern, Baltzerstrasse 1+3, 3012 Bern, Switzerland
^eInstitut für Geologie und Mineralogie, University of Cologne, Zülpicher Straße 49b, 50674 Köln, Germany
^fDepartment of Geosciences and Natural Resource Management, University of Copenhagen, Øster Voldgade 10, 1350 Copenhagen, Denmark
^gArchaeology, Environmental Changes, and Geo-Chemistry (AMGC) Research Group, Department of Chemistry, Vrije Universiteit Brussel, Pleinlaan 2, 1050 Brussels, Belgium

The late addition of extra-terrestrial material may represent an important source of Earth’s volatiles. The composition of impactors can be reconstructed using ⁵⁴Cr abundances in impact related rocks preserved in the terrestrial record. The average ε⁵³Cr and ε⁵⁴Cr of Earth’s mantle determined from mantle rocks of 3.8 Ga to present are 0.03 ± 0.02 and 0.08 ± 0.04, respectively. Impact melt rocks and spherule beds linked to impact structures larger than 50 km that formed between 3.4 Ga and 66 Ma have ε⁵³Cr ranging from −0.04 to 0.17, and ε⁵⁴Cr ranging from −0.64 to 1.41. A carbonaceous chondrite-like impactor contribution dominated the Meso- to Paleoarchean spherule layers (> 3.0 Ga), whereas a mixed chondrite flux composed of carbonaceous and non‑carbonaceous chondrites, with a possible contribution of differentiated meteorites is observed in the younger spherule layers (2.5 Ga to 66 Ma). This likely reflects the break-up of distinct asteroid families through time. Although available impact materials are limited, the Cr isotope signatures of materials related to large impacts suggest a change in the composition of crater-forming impactors on Earth, from predominantly carbonaceous chondrite-like more oxidized material during the Archean to predominantly non‑carbonaceous -like more reduced and volatile poor material in recent times. Chromium isotopes suggest that not >0.01 wt% of CC-like material added to the Earth’s mantle after Archean. Thus, it is inferred that the mass accreted after 3.0 Ga contributed insignificantly to the water and other volatile element budget of the Earth.

Zoë E. Wilbur¹, Timothy J. McCoy², Catherine M. Corrigan², Jessica J. Barnes¹, Sierra V. Brown³, Arya Udry⁴
Meteoritics & Planetary Science (in Press) Open Access
Link to Article [https://doi.org/10.1111/maps.14220]
¹Lunar and Planetary Laboratory, University of Arizona, Tucson, Arizona, USA
²Department of Mineral Sciences, National Museum of Natural History, Smithsonian Institution, Washington, District of
Columbia, USA
³Million Concepts, LLC, Louisville, Kentucky, USA
⁴University of Nevada, Las Vegas, Nevada, USA
Published by arrangement with John Wiley & Sons

Enstatite meteorites, both aubrites and enstatite chondrites, formed under exceptionally reducing conditions, similar to the planet Mercury. Despite being reduced, the MESSENGER mission showed that the surface of Mercury is more enriched in volatiles (e.g., S, Na, K, Cl) than previously thought. To better understand the mineral hosts of these volatiles and how they formed, this work examines the chemistry and petrographic settings of a rare, K-bearing sulfide called djerfisherite within enstatite chondrites and aubrites. The petrographic settings of djerfisherite within aubrites suggest this critical host of Cl formed after both the crystallization of troilite and exsolution of daubréelite. Djerfisherite is commonly observed as a rim on other sulfides and in contact with metal. We present an alteration model for djerfisherite formation in aubrite meteorites, whereby troilite and Fe-Ni metal are altered through anhydrous, alkali- and Cl-rich fluid metasomatism on the aubrite parent body to produce secondary djerfisherite. Moreover, we observe a loss of volatiles in djerfisherite within impact melted regions of the Miller Range 07139 EH3 chondrite and the Bishopville aubrite and explore the potential for impact devolatilization changes to sulfide chemistry on other reduced bodies in the Solar System. Vapor or fluid phase interactions are likely important in the formation of volatile-rich phases in reduced systems. While most Na and K on the mercurian surface is expected to be hosted in feldspar, djerfisherite is likely a minor, but critical, reservoir for K, Na, and Cl. Djerfisherite present on reduced bodies, such as Mercury, may represent sulfides formed via late-stage, primary metasomatism.

Akimasa Suzumura^1,3, Noriyuki Kawasaki², Hisayoshi Yurimoto², Shoichi Itoh¹
Meteoritics & Planetary Science (in Press) Open Access
Link to Article [https://doi.org/10.1111/maps.14222]
¹Department of Earth and Planetary Sciences, Kyoto University, Kyoto, Japan
²Department of Natural History Sciences, Hokkaido University, Sapporo, Japan
³Graduate School of Human and Environmental Studies, Kyoto University, Kyoto, Japan
Published by arrangement with John Wiley & Sons

A melilite-rich, compact type A Ca-Al-rich inclusion (CAI), KU-N-02, from the reduced CV3 chondrite Northwest Africa 7865, is mantled by an åkermanite-poor layer. We carried out a combined study of petrographic observations and in situ O and Al–Mg isotopic measurements for KU-N-02. The core shows a typical texture of igneous compact type A CAIs. The mantle consists of spinel, åkermanite-poor melilite, and perovskite. Individual mantle melilite crystals show reverse zoning toward the crystal grain boundary, in contrast to core melilite crystals showing normal zoning. The O isotopic compositions of the minerals in KU-N-02 plot along the carbonaceous chondrite anhydrous mineral line on a three O-isotope diagram. The mantle and core spinel crystals are uniformly ¹⁶O-rich (Δ¹⁷O ~ −23‰). The mantle melilite crystals exhibit variable O isotopic compositions ranging between Δ¹⁷O ~ −2‰ and −9‰, in contrast to the uniformly ¹⁶O-poor (Δ¹⁷O ~ −2‰) core melilite. The mantle melilite crystals also exhibit variable δ²⁵Mg values (δ²⁵Mg_DSM-3 ~ −2‰ to +3‰) compared with the nearly constant δ²⁵Mg values of the core melilite (δ²⁵Mg_DSM-3 ~ +2‰). The mantle minerals are likely to have formed by condensation from the solar nebular gas after core formation. The Al–Mg mineral isochrons of the core and mantle give initial ²⁶Al/²⁷Al ratios of (4.66 ± 0.15) × 10⁻⁵ and (4.74 ± 0.14) × 10⁻⁵, respectively. The age difference between the core and mantle formation is estimated to be within ~0.05 Myr, implying that both melting and condensation processes in the variable O isotopically solar nebular environments occurred within a short time during single CAI formation.

¹Paul H. Warren,²Junko Isa,¹Bidong Zhang,³Randy L. Korotev
Icarus (in Press) Open Access Link to Article [https://doi.org/10.1016/j.icarus.2024.116144]
¹Department of Earth, Planetary and Space Science, UCLA, Los Angeles, CA 90095, USA
²Cold Pine Observatory, 201, 4-22, Matsugaoka 1-cho me, Chigasaki, Kanagawa, Japan
³Department of Earth, Environmental, and Planetary Sciences, Washington University, St. Louis, MO 63130, USA
Copyright Elsevier

According to several orbital reflectance spectroscopy studies, numerous widely scattered lunar surface locales feature remarkably high (>98%) abundance of plagioclase. These “pure” anorthosite claims are based on an absorption band at ~1.25 μm, associated with minor Fe2+ within plagioclase. But utilization of the 1.25 μm band as a direct gauge of plagioclase abundance requires an underlying assumption that plagioclase FeO is uniform across all measured materials. Available data for FeO in lunar plagioclase are in many cases suspect because electron-probe FeO measurements may be inflated by secondary fluorescence from nearby mafic phases. We studied plagioclase FeO in a set of 13 anorthositic lunar rocks, taking care to avoid proximity to mafic phases; or in cases where complete avoidance was not possible without sacrificing representativeness (i.e., fine-grained impact melt rocks with zoned silicates), correcting close-to-mafic analyses for secondary fluorescence (Sugawara, T. [2001], Japanese Mag. Mineral. Petrol. Sci. 30, 159–163). Results for rock-average plagioclase FeO range from 0.030 wt% in plutonic troctolitic anorthosite 76,335, to 0.23 wt% in impact-melt rock 14,310. In general, as shown by exsolution of mafic silicates from plagioclase within several samples, final plagioclase FeO in lunar plutonic anorthosites is determined by reequilibration during slow postigneous cooling and/or metamorphism. In contrast, four fast-cooled anorthositic impact melt rocks have consistently higher plagioclase FeO, averaging 1.9 times higher in comparison to average plutonic anorthositic rock. Thus, impact melted lunar anorthosite will have far more prominent 1.25 μm absorption than plutonic anorthosite of the same plagioclase abundance. In view of the inconstancy of plagioclase FeO, orbital spectral reflectance using the 1.25 μm absorption band, or the ratio between that band and one or more mafic silicate bands, cannot be precise enough to justify claims of ability to resolve “purest” (98 vol% +) anorthosite from compositions that are high-plagioclase but not that extreme.

¹Addi Bischoff et al. (>10)
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.14193]
¹Institut für Planetologie, University of Münster, Münster, Germany
Published by arrangement with John Wiley & Sons

Elmshorn fell April 25, 2023, about 30 km northwest of the city of Hamburg (Germany). Shortly after the fall, 21 pieces were recovered totaling a mass of 4277 g. Elmshorn is a polymict and anomalous H3-6 chondritic, fragmental breccia. The rock is a mixture of typical H chondrite lithologies and clasts of intermediate H/L (or L, based on magnetic properties) chondrite origin. In some of the 21 pieces, the H chondrite lithologies dominate, while in others the H/L (or L) chondrite components are prevalent. The H/L chondrite assignment of these components is based on the mean composition of their olivines in equilibrated type 4 fragments (~Fa21–22). The physical properties like density (3.34 g cm−3) and magnetic susceptibility (logχ <5.0, with χ in 10−9 m3 kg−1) are typical for L chondrites, which is inconsistent with the oxygen isotope compositions: all eight O isotope analyses from two different fragments clearly fall into the H chondrite field. Thus, the fragments found in the strewn field vary in mineralogy, mineral chemistry, and physical properties but not in O isotope characteristics. The sample most intensively studied belongs to the stones dominated by H chondrite lithologies. The chemical composition and nucleosynthetic Cr and Ti isotope data are typical for ordinary chondrites. The noble gases in Elmshorn represent a mixture between cosmogenic, radiogenic, and primordially trapped noble gases, while a solar wind component can be excluded. Because the chondritic rock of Elmshorn contains (a) H chondrite parent body interior materials (of types 5 and 6), (b) chondrite parent body near-surface materials (of types 3 and 4), (c) fragments of an H/L chondrite (dominant in many stones), (d) shock-darkened fragments, and (e) clasts of various types of impact melts but no solar wind-implanted noble gases, the different components cannot have been part of a parent body regolith. The most straightforward explanation is that the fragmental breccia of Elmshorn represents a reaccreted rock after a catastrophic collision between an H chondrite parent body and another body with H/L (or L) chondrite characteristics but with deviating O isotope values (i.e. that of H chondrites), complete disruption of the bodies, mixing, and reassembly. This is the only straightforward way that the implantation of solar wind gases could have been avoided in this kind of complex breccia. The gas retention ages of about 2.8 Gyr possibly indicate the closure time after the catastrophic collision between H and H/L (or L) chondrite parent bodies, while the cosmic ray exposure age for Elmshorn, which had a preatmospheric radius of 25–40 cm, is ~17–20 Myr.