¹Noguchi, Takaaki et al. (>10)
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.14093]
¹Division of Earth and Planetary Sciences, Kyoto University, Kyoto, Japan
Published by arrangement with John Wiley & Sons

Samples returned from the carbonaceous asteroid (162173) Ryugu by the Hayabusa2 mission revealed that Ryugu is composed of materials consistent with CI chondrites and some types of space weathering. We report detailed mineralogy of the fine-grained Ryugu samples allocated to our “Sand” team and report additional space weathering features found on the grains. The dominant mineralogy is composed of a fine-grained mixture of Mg-rich saponite and serpentine, magnetite, pyrrhotite, pentlandite, dolomite, and Fe-bearing magnesite. These grains have mineralogy comparable to that of CI chondrites, showing severe aqueous alteration but lacking ferrihydrite and sulfate. These results are similar to previous works on large Ryugu grains. In addition to the major minerals, we also find many minerals that are rare or have not been reported among CI chondrites. Accessory minerals identified are hydroxyapatite, Mg-Na phosphate, olivine, low-Ca pyroxene, Mg-Al spinel, chromite, manganochromite, eskolaite, ilmenite, cubanite, polydymite, transjordanite, schreibersite, calcite, moissanite, and poorly crystalline phyllosilicate. We also show scanning transmission electron microscope and scanning electron microscope compositional maps and images of some space-weathered grains and severely heated and melted grains. Although our mineralogical results are consistent with that of millimeter-sized grains, the fine-grained fraction is best suited to investigate impact-induced space weathering.

^1,2Gabriel A. Pinto,³Emmanuel Jacquet,⁴Alexandre Corgne,²Felipe Olivares,¹Johan Villeneuve,¹Yves Marrocchi
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2023.11.012]
¹Université de Lorraine, CNRS, CRPG, UMR 7358, Vandœuvre-lès-Nancy, 54501, France
²INCT, Universidad de Atacama, Copayapu 485, Copiapó, Chile
³Institut de Minéralogie, de Physique des Matériaux et de Cosmochimie (IMPMC), Muséum national d’Histoire naturelle, Sorbonne Université, CNRS, CP52, 57 rue Cuvier, 75005 Paris, France
⁴Instituto de Ciencias de la Tierra, Universidad Austral de Chile, Valdivia, Chile
Copyright Elsevier

Ferromagnesian chondrules present a remarkable dichotomy between reduced (type I) and oxidized (type II) varieties. How these formed, and how they may be related remains contentious. Many type II chondrules, especially in carbonaceous chondrites, contain forsteritic grains in disequilibrium with FeO-rich host olivine grains, which must be relicts of precursor material. In this study, we analyzed the oxygen isotopic composition of magnesian relict and host olivine grains in type II chondrules in CO and CR chondrites. The analyzed Mg-rich relicts are generally more 16O-rich than ferroan olivine (mostly host) grains and plot in the range (in term of chemistry and isotopic composition) of type I chondrules in carbonaceous chondrites. Remarkably, they tend to cluster around the dominant Δ17O peaks of the type I chondrules in their host chondrites, viz. –6 ‰ and –2 ‰ for CO and CR, respectively. With the occurrence of relatively intact type I chondrules within some type II chondrules, this corroborates that local type I chondrules were among the precursors of type II chondrules, and that chondrule formation occurred within the accretion reservoir of the eventual chondrites. This supports the nebular brand of chondrule-forming scenarios. Since not all previous generations of chondrules (or other precursor objects) have been recycled, chondrule formation events must also have been extremely localized.

¹Mathieu Roskosz et al. (>10)
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.14098]
¹Institut de Minéralogie, Physique des Matériaux et Cosmochimie, Muséum National d’Histoire Naturelle, CNRS UMR 7590, Sorbonne Université, Paris, France
Published by arrangement with John Wiley & Sons

The Hayabusa2 mission sampled Ryugu, an asteroid that did not suffer extensive thermal metamorphism, and returned rocks to the Earth with no significant air exposure. It therefore offers a unique opportunity to study the redox state of carbonaceous Cb-type asteroids and evaluate the overall redox state of the most primitive rocks of the solar system. An analytical framework was developed to investigate the iron mineralogy and valence state in extraterrestrial material at the micron scale by combining x-ray diffraction, conventional Mössbauer (MS), and nuclear forward scattering (NFS) spectroscopies. An array of standard minerals was analyzed and cross-calibrated between MS and NFS. Then, MS and NFS spectra on three Ryugu grains were collected at the bulk and the micron scales. In Ryugu samples, iron is essentially accommodated in magnetite, clay minerals (serpentine–smectite), and sulfides. Only a single set of Mössbauer parameters was necessary to account for the entire variability observed in MS and NFS spectra, at all spatial scales investigated. These parameters therefore make up a fully consistent iron mineralogical model for the Ryugu samples. As far as MS and NFS spectroscopies are concerned, Ryugu grains are overall similar to each other and share most of their mineralogical features with CI-type chondrites. In detail however, no ferrihydrite is found in Ryugu particles even at the very sensitive scale of Mössbauer spectroscopy. The typical Fe3+/Fetot of clay minerals is much lower than typical redox ratios measured in CI chondrites (Fe3+/Fetot = 85%–90%). Furthermore, magnetite from Ryugu is stoichiometric with no significant maghemite component, whereas up to 12% of maghemite was previously identified in the Orgueil’s so-called magnetite. These differences suggest that most CI meteorites suffered terrestrial alteration and that the preterrestrial composition of these carbon-rich samples was less oxidized than previously measured. However, it is not clear yet whether or not the parent bodies of CI chondrites were as reduced as Ryugu. Finally, the high spatial resolution of NFS allows to disentangle the redox state and the crystal chemistry of iron accommodated in serpentine and smectite. The most likely polytype of serpentine is lizardite, containing <35% of Fe3+, a fraction of which being tetrahedrally coordinated. Smectite is more oxidized (Fe3+/Fetot > 65%) and mainly contains octahedral ferric iron. This finding implies that these clays formed from highly alkaline fluids and the spatial variability highlighted here may suggest a temporal evolution or a spatial variability of the nature of this fluid.

¹Yan Hu et al. (>10)
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2023.115884]
¹Université Paris Cité, Institut de Physique du Globe de Paris, CNRS, 75005 Paris, France
Copyright Elsevier

C-type asteroids are the presumed home to carbonaceous chondrites, some of which contain abundant life-forming volatiles and organics. For the first time, samples from a C-type asteroid (162,173 Ryugu) were successfully returned to Earth by JAXA’s Hayabusa2 mission. These pristine samples, uncontaminated by the terrestrial environment, allow a direct comparison with carbonaceous chondrites. This study reports the stable K isotopic compositions (expressed as δ41K) of Ryugu samples and seven carbonaceous chondrites to constrain the origin of K isotopic variations in the early Solar System. Three aliquots of Ryugu particles collected at two touchdown sites have identical δ41K values, averaged at −0.194 ± 0.038‰ (2SD). The K isotopic composition of Ryugu falls within the range of δ41K values measured on representative CI chondrites, and together, they define an average δ41K value of −0.185 ± 0.078‰ (2SE), which provides the current best estimate of the K isotopic composition of the bulk Solar System. Samples of CI chondrites with δ41K values that deviate from this range likely reflect terrestrial contaminations or compositional heterogeneities at sampled sizes. In addition to CI chondrites, substantial K isotopic variability is observed in other carbonaceous chondrites and within individual chondritic groups, with δ41K values inversely correlated with K abundances in many cases. These observations indicate widespread fluid activity occurred in chondrite parent bodies, which significantly altered the original K abundances and isotopic compositions of chondrules and matrices established at their accretion.

¹Jie-Jun Jing,²Jasper Berndt,²Stephan Klemme,¹Wim van Westrenen
Geochimica et Cosmochimica Acta (in Press) Open Access Link to Article [https://doi.org/10.1016/j.gca.2023.11.011]
¹Department of Earth Sciences, Faculty of Science, Vrije Universiteit Amsterdam, De Boelelaan 1085, 1081 HV Amsterdam, The Netherlands
²Institut für Mineralogie, Westfälische Wilhelms-Universität Münster, Correnstraße 24, D48149 Münster, Germany
Copyright Elsevier

To quantify fluorine (F) evolution during lunar magma ocean (LMO) crystallization, high-pressure, high-temperature experiments have been conducted to determine mineral-melt partitioning of F for lunar minerals (plagioclase, orthopyroxene and ilmenite). Results constrain the F abundance in the magma ocean to 21-41 ppm at the time crust-forming plagioclase started crystallizing. Forward modeling shows that 352-703 ppm F would remain in the final 1% of magma toward the end of magma ocean solidification. This range overlaps that inferred for the urKREEP reservoir (660 ppm). Taking into account model uncertainties, from the perspective of F abundances the urKREEP reservoir can be formed at 98.9-99.5 per cent LMO solidification, with negligible loss of F from the Moon since the onset of crust formation. Backward modeling from initial crust-forming plagioclase, an initial LMO would contain 4.2-8.5 ppm F, which is consistent with estimates of the lunar primitive mantle F content derived from melt inclusions in Apollo samples. This finding is consistent with previous suggestions that the bulk silicate Moon is depleted in F relative to the bulk silicate Earth (which contains ∼25 ppm F). A BSE-like initial LMO would yield a magma containing 122 ppm F at the onset of crust formation, significantly higher than our calculated 21-41 ppm F. Fluorine depletion could have occurred by degassing during the early LMO stages (between the onset of LMO crystallization and first crust formation), and/or prior to the LMO stage (e.g., depletion during the giant impact or vapor drainage in the protolunar disk), but seems to have ended by the time the crust started forming.

¹Jingyou Chen, ²Ying Wang, ³Ai-Cheng Zhang, ²Shiyong Liao, ⁴Shaolin Li, ¹Sky Beard, ¹Meng-Hua Zhu
Journal of Geopyhsical Research (Planets)(in Press) Link to Article [https://doi.org/10.1029/2023JE007954]
¹State Key Laboratory of Lunar and Planetary Sciences, Macau University of Science and Technology, Macau, China
²CAS Center for Excellence in Comparative Planetology, Purple Mountain Observatory, Nanjing, China
³State Key Laboratory for Mineral Deposits Research and School of Earth Science and Engineering, Nanjing University, Nanjing, China
⁴Astronomical Research Center, Shanghai Science & Technology Museum, Shanghai, China
Published by arrangement with John Wiley & Sons

Mesosiderites are thought to be created by a catastrophic impact that mixes the silicate crust with the metallic core of a differentiated asteroid(s). The metal-silicate mixing event greatly affects the subsequent geological evolution of the mesosiderite parent body. To gain a better understanding of this mixing event, we carried out studies on olivine alteration and merrillite Pb-Pb thermochronology in the Dong Ujimqin Qi mesosiderite. The primary olivine in this meteorite has been altered through sulfidation reactions, leading to the formation of troilite-orthopyroxene intergrowths. This alteration likely took place during metal-silicate mixing, as the mixing environment can provide favorable chemical and thermal conditions for this reaction. Phosphate-chromite veins crosscutting the troilite-orthopyroxene intergrowths indicate a secondary alteration process likely induced by subsequent impacts. Additionally, the metal-silicate mixing event likely contributed to the occurrence of abundant merrillites at the boundary between silicates and Fe-Ni metals, as supported by the distinctly depleted incompatible elements resulting from the redox reaction between metals and adjacent silicates. The ion microprobe analyses for these merrillites yielded a Pb-Pb age of 4,064 ± 120 Ma, which is interpreted as the record of the Pb isotopic closure of merrillite during prolonged cooling associated with the deep burial. Our two-stage cooling model suggests that the mesosiderite parent body’s burial potentially started around 4.52 Ga, which is consistent with the Sm-Nd, Ar-Ar, and Pb-Pb thermochronological records in mesosiderites.

¹D. Paul,¹S. Dhoundiyal,¹M. Aranha,¹A. Porwal,²G. Thangjam
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2023.115865]
¹CSRE Department, IIT Bombay, Powai-400076, India
²School of Earth and Planetary Sciences, NISER, HBNI, Bhubaneswar 752050, India
Copyright Elsevier

Pyroxene chemistry estimated using a series of spectral parameters derived from Chandrayaan-I M3 data was used to divide the basalts of Mare Humorum into six compositional units. In order to understand the petrogenetic history of the Humorum basalts, first, the dominant pyroxene end-member composition in each unit is used to estimate the temperature of crystallization; and then crater counting is implemented using craters mapped from the high-resolution Kaguya Terrain Camera data to estimate the age of each unit. The spatial distributions of pyroxene composition and corresponding crystallization temperatures indicate that there is a difference in volcanic activity between the regions corresponding to Units 1–3 (Group I) and the regions corresponding to Units 4–6 (Group II). This observation is further reinforced by analyzing the variation of FeO and TiO2 content across the units. Hence two sources ilmenite-rich HCP and low ilmenite HCP correspond to two groups of basalts in the Humorum area. Furthermore, our new crater-counting analysis reveals that the magmatic activity probably continued until ca. 1.9 Ga in the Humorum basin. To the best of our knowledge, this younger age of volcanism has not been reported before.

¹A. Goodwin,¹R. Tartèse,¹R. J. Garwood,²N. V. Almeida
Journal of Geophysical Research (Planets)(in Press) Open Access Link to Article [https://doi.org/10.1029/2023JE007916]
¹Department of Earth and Environmental Sciences, The University of Manchester, Manchester, UK
²Natural History Museum, London, UK
Published by arrangement with John Wiley & Sons

The Martian regolith breccia Northwest Africa (NWA) 11220 and paired stones represent the only known meteorites that sample a clastic sub-surface lithology from Mars. By applying X-ray computed microtomography to monomineralic clasts, we identify three phases that can be automatically segmented by thresholding X-ray attenuation greyscale values: (A) feldspars, (B) pyroxene and apatite, and (C) iron-rich oxides and sulfides, confirmed via scanning electron microscopy and Raman spectroscopy. For these three phases, we demonstrate scale invariance in size and shape for sand-sized clasts and smaller, a characteristic commonly observed for clast populations generated by fragmentation without further sorting from sedimentary transport (e.g., Aeolian or fluvial processes). Additionally, by assessing the preferred orientation of fitted ellipses and ellipsoids to manually segmented proto-breccia clasts in two and three dimensions, we identified a weak planar fabric that likely resulted from compaction rather than impact transport. Combining clast size distribution with evidence for nested textures inside proto-breccia clasts, we propose that NWA 11220 has experienced a minimum of two hypervelocity impact events and should be considered a lithified impact ejecta lithology with little to no reworking via surface regolith processes.

^1,2G. Massa,²E. Palomba,²A. Longobardo,^1,2M. Angrisani,^1,2C. Gisellu,²F. Dirri,²M.C. De Sanctis,²A. Raponi,²F.G. Carrozzo,²M. Ciarniello
Icarus (in Press) Open Access Link to Article [https://doi.org/10.1016/j.icarus.2023.115870]
¹University of Rome “Sapienza”, Piazzale Aldo Moro 5, Rome 00185, Italy
²INAF Istituto di Astrofisica e Planetologia Spaziali, via Fosso del Cavaliere, Rome 00133, Italy
Copyright Elsevier

NASA’s Dawn mission was launched in September 2007 and orbited asteroids Vesta (2011−2012) and Ceres (2015–2018). Vesta shows surface dark units that have been suggested to be linked to exogenous materials and are therefore useful to understand the initial stages of the Solar System.

This work takes advantage of the newly calibrated data of the VIR spectrometer, which are characterized by a better signal to noise (S/N) ratio, giving us the opportunity to search for spectral features that were never seen before due to noise. Considering that hydroxyl has been shown to be present in every dark unit on Vesta and also in carbonaceous chondrites, the goals of this work are the search for and characterization of carbonates that are present in carbonaceous chondrites, i.e., the supposed darkening agents of Vesta.

The estimate of the abundances of carbonates is fundamental to identify which carbonaceous chondrite fell on Vesta; this can be crucial for the definition of an evolutionary history of Vesta and the Solar System. The study of a possible feature at 3.9 μm related to the presence of carbonates was analyzed and found to be noise-induced. Although spectral features related to carbonates were not observed, the 3.4 μm absorption band was analyzed anyway in order to fix an upper limit to the abundance of carbonates in carbonaceous chondrites on Vesta. This value is consistent with petrochemical analyses, i.e., no more than 0.2% of carbonates in carbonaceous chondrites.

¹T. A. Harvey,¹J. L. MacArthur,¹K. H. Joy,^2,3D. Sykes,⁴N. V. Almeida, R. H. Jones
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.14094]
¹Department of Earth and Environmental Sciences, The University of Manchester, Manchester, UK
²Henry Moseley X-Ray Imaging Facility, The Royce Institute, School of Materials, The University of Manchester, Manchester, UK
³Physical Intelligence Department, Max Planck Institute for Intelligent Systems, Stuttgart, Germany
⁴Planetary Materials Group, Natural History Museum, London, UK
Published by arrangement with John Wiley & Sons

Photogrammetry is a low-cost, nondestructive approach for producing 3-D models of meteorites for the purpose of determining sample bulk density. Coupled with the use of a nondestructive magnetic susceptibility/electrical conductivity field probe, we present measurements for the interrogation of several physical properties, on a set of Antarctic meteorites. Photogrammetry is an effective technique over a range of sample sizes, with meteorite bulk density results that are closely comparable with literature values, determined using Archimedean glass bead or laser scanning techniques. The technique is completely noncontaminating and suitable for the analysis of rare or fragile samples, although there are limitations for analyzing reflective samples. It is also flexible, and, with variations in equipment setup, may be appropriate for samples of a wide range of sizes. X-ray computed tomography analyses of the same meteorite samples yielded slightly different bulk density results, predominantly for samples below 10 g, although the reason for this is unclear. Such analyses are expensive and potentially damaging to certain features of the sample (e.g., organic compounds), but may be useful in expanding the measurements to accommodate an understanding of internal voids within the sample, lending itself to measurement of grain density. Measurements of bulk density are valuable for comparisons with estimates of the bulk densities of asteroids that are suggested as meteorite parent bodies.