^1,2Yun Jiang et al. (>10)
The Astrophysical Journal Letters 945, L26 Open Access Link to Article [DOI 10.3847/2041-8213/acbd31]
¹CAS Key Laboratory of Planetary Sciences, Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing 210023, People’s Republic of China
²Center for Excellence in Comparative Planetology, Chinese Academy of Sciences, Hefei 230026, People’s Republic of China

The Chang’E 5 (CE-5) samples represent the youngest mare basalt ever known and provide an access into the late lunar evolution. Recent studies have revealed that CE-5 basalts are the most evolved lunar basalts, yet controversy remains over the nature of their mantle sources. Here we combine Fe and Mg isotope analyses with a comprehensive study of petrology and mineralogy on two CE-5 basalt clasts. These two clasts have a very low Mg# (∼29) and show similar Mg isotope compositions to Apollo low-Ti mare basalts as well as intermediate TiO2 and Fe isotope compositions between low-Ti and high-Ti mare basalts. Fractional crystallization or evaporation during impact cannot produce such geochemical signatures that otherwise indicate a hybrid mantle source that incorporates both early- and late-stage lunar magma ocean (LMO) cumulates. Such a hybrid mantle source would be also compatible with the KREEP-like Rare Earth Elements pattern of CE-5 basalts. Overall, our new Fe–Mg isotope data highlight the role of late LMO cumulate for the generation of young lunar volcanism.

¹Hiroaki Kaneko,¹Kento Sato,¹Chihiro Ikeda,¹Taishi Nakamoto
The Astrophysical Journal 947, 15 Open Access Link to Article [DOI 10.3847/1538-4357/acb20e]
¹Department of Earth and Planetary Sciences, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo 152-8550 Japan; kaneko.h.aq@m.titech.ac.jp

Among the several candidate models for chondrule formation, the lighting model has been recognized to be less likely than the other two major models, shock-wave heating and planetesimal collision. It might be because we have believed that the lightning model predicts cooling rates of chondrules that are too fast to reproduce their textures with the assumption that the discharge channels must be optically thin. However, the previous works revealed that the buildup of a strong electric field to generate the lightning in protoplanetary disks requires the enhancement of the solid density. Moreover, some properties of chondrules indicate their formation in environments with such a high solid density. Therefore, the discharge channels may be optically thick, and the lightning model can potentially predict the proper cooling rates of chondrules. In this study, we reinvestigate the cooling rates of chondrules produced by the lightning in the solid-rich environments considering the radiative transfer and the expansion of the hot channel. Chondrules must interact dynamically with the surrounding gas and dust via the drag force. We consider two limiting cases for the dynamics of chondrules: the drag force is ignored in the first case, and chondrules are completely coupled with their surroundings in the second case. In both cases, the lightning model predicts the proper cooling rates of chondrules under the optically thick conditions with high solid enhancement. Therefore, the lightning model is worth further investigation to judge its reliability as the source of chondrule formation.

¹R.Brunetto et al. (>10)
The Astrophysical Journal Letters 951, L33 Open Access Link to Article [DOI 10.3847/2041-8213/acdf5c]
¹1 IAS, Université Paris-Saclay, CNRS, France; rosario.brunetto@universite-paris-saclay.fr

Ryugu is a second-generation C-type asteroid formed by the reassembly of fragments of a previous larger body in the main asteroid belt. While the majority of Ryugu samples returned by Hayabusa2 are composed of a lithology dominated by aqueously altered minerals, clasts of pristine olivine and pyroxene remain in the least-altered lithologies. These clasts are objects of great interest for revealing the composition of the dust from which the original building blocks of Ryugu’s parent asteroid formed. Here we show that some grains rich in olivine, pyroxene, and amorphous silicates discovered in one millimeter-sized stone of Ryugu have infrared spectra similar to the D-type asteroid Hektor (a Jupiter Trojan), to comet Hale–Bopp, and to some anhydrous interplanetary dust particles of probable cometary origin. This result indicates that Ryugu’s primary parent body incorporated anhydrous ingredients similar to the building blocks of asteroids (and possibly some comets) formed in the outer solar system, and that Ryugu retained valuable information on the formation and evolution of planetesimals at different epochs of our solar system’s history.

^1,2Martin Bizarro et al. (>10)
The Astrophysical Journal Letters 958, L25 Open Access Link to Article [DOI 10.3847/2041-8213/ad09d9]
¹Centre for Star and Planet Formation, Globe Institute, University of Copenhagen, DK-1350 Copenhagen K, Denmark; bizzarro@sund.ku.dk
²Université Paris Cité, Institut de Physique du Globe de Paris, CNRS, F-75005 Paris, France

The nucleosynthetic isotope composition of planetary materials provides a record of the heterogeneous distribution of stardust within the early solar system. In 2020 December, the Japan Aerospace Exploration Agency Hayabusa2 spacecraft returned to Earth the first samples of a primitive asteroid, namely, the Cb-type asteroid Ryugu. This provides a unique opportunity to explore the kinship between primitive asteroids and carbonaceous chondrites. We report high-precision μ26Mg* and μ25Mg values of Ryugu samples together with those of CI, CM, CV, and ungrouped carbonaceous chondrites. The stable Mg isotope composition of Ryugu aliquots defines μ25Mg values ranging from –160 ± 20 ppm to –272 ± 30 ppm, which extends to lighter compositions relative to Ivuna-type (CI) and other carbonaceous chondrite groups. We interpret the μ25Mg variability as reflecting heterogeneous sampling of a carbonate phase hosting isotopically light Mg (μ25Mg ∼ –1400 ppm) formed by low temperature equilibrium processes. After correcting for this effect, Ryugu samples return homogeneous μ26Mg* values corresponding to a weighted mean of 7.1 ± 0.8 ppm. Thus, Ryugu defines a μ26Mg* excess relative to the CI and CR chondrite reservoirs corresponding to 3.8 ± 1.1 and 11.9 ± 0.8 ppm, respectively. These variations cannot be accounted for by in situ decay of 26Al given their respective 27Al/24Mg ratios. Instead, it requires that Ryugu and the CI and CR parent bodies formed from material with a different initial 26Al/27Al ratio or that they are sourced from material with distinct Mg isotope compositions. Thus, our new Mg isotope data challenge the notion that Ryugu and CI chondrites share a common nucleosynthetic heritage.

¹Yves Marrocchi,^1,2Maxime Piralla,³François L. H. Tissot
The Astrophysical Journal Letters 954, L27 Open Access Link to Article [DOI 10.3847/2041-8213/acefd1]
¹Centre de recherches pétrographiques et géochimiques (CRPG), CNRS, UMR 7358, F-54000, Nancy, France; yvesm@crpg.cnrs-nancy.fr
²Max Planck Institute for Solar System Research, Justus-von-Liebig-Weg 3, D-37077 Göttingen, Germany
³The Isotoparium, Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125, USA

The recent advent of nontraditional isotopic systems has revealed that meteorites display a fundamental isotopic dichotomy between noncarbonaceous (NC) and carbonaceous (C) groups, which represent material from the inner and outer solar system, respectively. On the basis of iron isotope anomalies, this view has recently been challenged in favor of a circumsolar disk structured into three distinct reservoirs (the so-called isotopic trichotomy). In this scenario, the CI chondrites—a rare type of carbonaceous chondrites with chemical composition similar to that of the Sun’s photosphere—would sample a distinct source region than other carbonaceous chondrites, located beyond Saturn’s orbit. Here, we report a model based on the available data for both mass-dependent fractionation of Te stable isotopes and mass-independent Fe nucleosynthetic anomalies. On the basis of the Te–Fe isotopic correlation defined by all carbonaceous chondrites including CIs, we show that the NC-CC dichotomy extends to Fe isotopes. Our finding thus supports (i) the existence of only two reservoirs in the early solar system and (ii) the ubiquitous presence of CI-like dust throughout the carbonaceous reservoir. Our approach also reveals that the carrier phase of 54Fe anomalies corresponds to Fe–Ni metal beads mostly located within chondrules. Finally, we propose that the CC chondrule component records a constant mix of refractory inclusions and NC-like dust.

¹Antonio Lanzirotti,^1,2Stephen R. Sutton,¹Matthew Newville,³Adrian Brearley,⁴Oliver Tschauner
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.14130]
¹Center for Advanced Radiation Sources, The University of Chicago, Argonne, Illinois, USA
²Department of the Geophysical Sciences, The University of Chicago, Argonne, Illinois, USA
³Earth and Planetary Sciences, University of New Mexico, Albuquerque, New Mexico, USA
⁴Department of Geoscience, University of Nevada Las Vegas, Las Vegas, Nevada, USA
Published by arrangement with John Wiley & Sons

This study describes the application of new synchrotron X-ray fluorescence (XRF) and diffraction (XRD) microtomographies for the 3-D visualization of chemical and mineralogical variations in unsectioned extraterrestrial samples. These improved methods have been applied to three compositionally diverse chondritic meteorite samples that were between 300 and 400 μm in diameter, including samples prepared from fragments of the CR2 chondrite LaPaz Icefield (LAP) 02342, H5 chondrite MacAlpine Hills (MAC) 88203, and the CM2 chondrite Murchison. The synchrotron-based XRF and XRD tomographies used are focused-beam techniques that measure the intensities of fluorescent and diffracted X-rays in a sample simultaneously during irradiation by a high-energy microfocused incident X-ray beam. Measured sinograms of the emitted and diffracted intensities were then tomographically reconstructed to generate 2-D slices of XRF and XRD intensity through the sample, with reconstructed pixel resolution of 1–2 μm, defined by the resolution of the focused incident X-ray beam. For sample LAP 02342, primary mineral phases that were visualized in reconstructed slices using these techniques included isolated grains of α-Fe, orthopyroxene, and olivine. For our sample of MAC 88203, XRF/XRD tomography allowed visualization of forsteritic olivine as a primary mineral phase, a vitrified fusion crust at the sample surface, identification of localized Cr-rich spinels at spatial resolutions of several micrometers, and imaging of a plagioclase-rich glassy matrix. In the sample of Murchison, major identifiable phases include clinoenstatite- and olivine-rich chondrules, variable serpentine matrix minerals and small Cr-rich spinels. Most notable in the tomographic analysis of Murchison is the ability to quantitatively distinguish and visualize the complex mixture of serpentine-group minerals and associated tochilinite–cronstedtite intergrowths. These methods provide new opportunities for spatially resolved characterization of sample texture, mineralogy, crystal structure, and chemical state in unsectioned samples. This provides researchers an ability to characterize such samples internally with minimal disruption of sample micro-structures and chemistry, possibly without the need for sample extraction from some types of sampling and capture media.

¹José C. Aponte,^1,2,3Frédéric Séguin,^1,4Ariel J. Siguelnitzky,¹Jason P. Dworkin,¹Jamie E. Elsila,¹Daniel P. Glavin,^5,6,7Harold C. Connolly Jr,⁵Dante S. Lauretta
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.14118]
¹Solar System Exploration Division, NASA Goddard Space Flight Center, Greenbelt, Maryland, USA
²Department of Physics, The Catholic University of America, Washington, DC, USA
³Center for Research and Exploration in Space Science and Technology, NASA Goddard Space Flight Center, Greenbelt, Maryland, USA
⁴Sig Engineering LLC, Laurel, Maryland, USA
⁵Lunar and Planetary Laboratory, University of Arizona, Tucson, Arizona, USA
⁶Department of Geology, School of Earth and Environment, Rowan University, Glassboro, New Jersey, USA
⁷Department of Earth and Planetary Science, American Museum of Natural History, New York, New York, USA
Published by arrangement with John Wiley & Sons

Volatile organic compounds (VOCs) are carbon-containing chemicals that may evaporate rapidly at room temperature and standard pressure. Such organic compounds can be preserved inside carbonaceous chondrite matrices. However, unlike meteoritic soluble organic matter (SOM) and insoluble organic matter (IOM), VOCs are typically lost (at least in part) during sample processing (meteorite crushing) and exposure to terrestrial atmosphere and/or solvents. Like SOM and IOM, VOCs can provide valuable insights into the chemical inventory of the meteorite parent body and even the presolar cloud from which our solar system formed, as well as the composition and processes that occurred during the early formation of our solar system and the asteroidal stage. Thus, in this work, we designed and built an instrument that allowed us to access the VOCs present in samples of the carbonaceous chondrites Murchison and Sutter’s Mill after mineral disaggregation by means of freeze–thaw cycling. We simultaneously evaluated the abundances and compound-specific 13C-distributions of the volatiles evolving after meteorite powdering at ~20, 60, and 100°C. Carbon monoxide (CO) and methane (CH4) were released from these meteorites as the most abundant VOCs. They were combusted together for analysis and showed positive δ13C values, indicative of their extraterrestrial origins. Carbon dioxide (CO2) was also an abundant VOC in both meteorites, and its isotopic values suggest that it was mainly formed from dissolved carbonates in the samples. We also detected aldehydes, ketones, and aromatic compounds in low amounts. Contrary to Murchison, which mostly yielded VOCs with positive δ13C values, Sutter’s Mill yielded VOCs with negative δ13C values. The less enriched 13C isotope composition of the VOCs detected in Sutter’s Mill suggest that they are either terrestrial contaminants, such as VOCs in compressed gas dusters and common laboratory solvents, or compounds disconnected from interstellar sources and/or formed through parent body processing. Understanding the relative abundances and determining the molecular distributions and isotopic compositions of free meteoritic VOCs are key in assessing their extraterrestrial origins and those of chondritic SOM and IOM. Our newly developed technique will be valuable in the study of the samples brought to the Earth from carbonaceous asteroid Bennu by NASA’s OSIRIS-REx mission.

¹Yuji Matsumoto,²Sota Arakawa
The Astrophysical Journal 948, 73 Open Access Link to Article [DOI 10.3847/1538-4357/acc57c]
¹National Astronomical Observatory of Japan, 2-21-1, Osawa, Mitaka, 181-8588 Tokyo, Japan; yuji.matsumoto@nao.ac.jp
²Japan Agency for Marine-Earth Science and Technology, 3173-25, Showa-machi, Kanazawa-ku, Yokohama, Kanagawa 236-0001, Japan

Shock-wave heating is a leading candidate for the mechanisms of chondrule formation. This mechanism forms chondrules when the shock velocity is in a certain range. If the shock velocity is lower than this range, dust particles smaller than chondrule precursors melt, while chondrule precursors do not. We focus on the low-velocity shock waves as the igneous rim accretion events. Using a semianalytical treatment of the shock-wave heating model, we found that the accretion of molten dust particles occurs when they are supercooling. The accreted igneous rims have two layers, which are the layers of the accreted supercooled droplets and crystallized dust particles. We suggest that chondrules experience multiple rim-forming shock events.

¹Steven J. Desch,^2,3Emilie T. Dunham,¹Ashley K. Herbst,⁴Cayman T. Unterborn,¹Thomas G. Sharp,¹Maitrayee Bose,⁵Prajkta Mane,⁶Curtis D. Williams
The Astrophysical Journal 953, 146 Open Access Link to Article [DOI 10.3847/1538-4357/acdeed]
¹School of Earth and Space Exploration, Arizona State University, P.O. Box 871404, Tempe, AZ 85287-1404, USA; steve.desch@asu.edu
²Department of Earth, Planetary and Space Sciences, University of California, Los Angeles, CA 90095, USA
³Department of Earth and Planetary Sciences, University of California, Santa Cruz, CA 95064, USA
⁴Southwest Research Institute, 6220 Culebra Road, San Antonio, TX 78238, USA
⁵Lunar and Planetary Institute, 3600 Bay Area Boulevard, Houston, TX 77058, USA
⁶Arctic Slope Regional Corporation Federal, 11091 Sunset Hills Road, Suite 800, Reston, VA 20190, USA

Most meteoritic calcium-rich, aluminum-rich inclusions formed from a reservoir with ²⁶Al/²⁷Al ≈ 5 × 10⁻⁵, but some record lower (26Al/27Al)0, demanding they sampled a reservoir without live ²⁶Al. This has been interpreted as evidence for “late injection” of supernova material into our protoplanetary disk. We instead interpret the heterogeneity as chemical, demonstrating that these inclusions are strongly associated with the refractory phases corundum or hibonite. We name them “low-²⁶Al/²⁷Al corundum/hibonite inclusions” (LAACHIs). We present a detailed astrophysical model for LAACHI formation in which they derive their Al from presolar corundum, spinel, or hibonite grains 0.5–2 μm in size with no live ²⁶Al; live ²⁶Al is carried on smaller (<50 nm) presolar chromium spinel grains from recent nearby Wolf–Rayet stars or supernovae. In hot (≈1350–1425 K) regions of the disk, these grains and perovskite grains would be the only survivors. These negatively charged grains would grow to sizes 1–10³μm, even incorporating positively charged perovskite grains, but not the small, negatively charged ²⁶Al-bearing grains. Chemical and isotopic fractionations due to grain charging was a significant process in hot regions of the disk. Our model explains the sizes, compositions, oxygen isotopic signatures, and the large, correlated ⁴⁸Ca and ⁵⁰Ti anomalies (if carried by presolar perovskite) of LAACHIs, and especially how they incorporated no ²⁶Al in a solar nebula with uniform, canonical ²⁶Al/²⁷Al. A late injection of supernova material is obviated, although formation of the Sun in a high-mass star-forming region is demanded.

^1,2Prajkta Mane,¹Maitrayee Bose,¹Meenakshi Wadhwa,^3,4Céline Defouilloy
The Astrophysical Journal 946, 37 Open Access Link to Article [DOI 10.3847/1538-4357/acb156]
¹School of Earth and Space Exploration, Arizona State University, Tempe, AZ 85287, USA; pmane@lpi.usra.edu
²Lunar and Planetary Institute, Universities Space Research Association, Houston, TX 77058, USA
³WiscSIMS, Department of Geoscience, University of Wisconsin-Madison, Madison, WI 53706, USA
⁴CAMECA, F-92622 Gennevilliers Cedex, France

The calcium–aluminum-rich inclusions (CAIs) from chondritic meteorites are the first solids formed in the solar system. Rim formation around CAIs marks a time period in early solar system history when CAIs existed as free-floating objects and had not yet been incorporated into their chondritic parent bodies. The chronological data on these rims are limited. As seen in the limited number of analyzed inclusions, the rims formed nearly contemporaneously (i.e., <300,000 yr after CAI formation) with the host CAIs. Here we present the relative ages of rims around two type B CAIs from NWA 8323 CV3 (oxidized) carbonaceous chondrite using the 26Al–26Mg chronometer. Our data indicate that these rims formed ∼2–3 Ma after their host CAIs, most likely as a result of thermal processing in the solar nebula at that time. Our results imply that these CAIs remained as free-floating objects in the solar nebula for this duration. The formation of these rims coincides with the time interval during which the majority of chondrules formed, suggesting that some rims may have formed in transient heating events similar to those that produced most chondrules in the solar nebula. The results reported here additionally bolster recent evidence suggesting that chondritic materials accreted to form chondrite parent bodies later than the early-formed planetary embryos, and after the primary heat source, most likely 26Al, had mostly decayed away.