¹Christian A. Jansen,^1,2Christoph Burkhardt,³Yves Marrocchi,^1,2Jonas M. Schneider,^1,2Elias Wölfer,^1,2Thorsten Kleine
Earth and Planetary Science Letters 627, 118567 Open Access Link to Article [https://doi.org/10.1016/j.epsl.2024.118567]
¹Institut für Planetologie, University of Münster, Wilhelm-Klemm-Straße 10, Münster D-48149, Germany
²Max Planck Institute for Solar System Research, Justus-von-Liebig-Weg 3, Göttingen D-37077, Germany
³Centre de recherches pétrographiques et géochimiques (CRPG), CNRS, UMR 7358, F-54000, Nancy, France
Copyright Elsevier

Refractory inclusions in chondritic meteorites, namely amoeboid olivine aggregates (AOAs) and Ca-Al-rich inclusions (CAIs), are among the first solids to have formed in the solar system. The isotopic composition of CAIs is distinct from bulk meteorites, which either results from extreme processing of presolar carriers in the CAI-forming region, or reflects an inherited heterogeneity from the Sun’s parental molecular cloud. Amoeboid olivine aggregates are less refractory than CAIs and provide a record of how the isotopic composition of solid material in the disk may have changed in time and space. However, the isotopic composition of AOAs and how this composition relates to that of CAIs and later-formed solids is unknown. Here, using new O, Ti, and Cr isotopic data for eight AOAs from the Allende CV3 chondrite, we show that CAIs and AOAs share a common isotopic composition, indicating a close genetic link and formation from the same isotopic reservoir. Because AOAs are less refractory than CAIs, this observation is difficult to reconcile with a thermal processing origin of the isotope anomalies. Instead, the common isotopic composition of CAIs and AOAs is readily accounted for in a model in which the isotopic composition of infalling material from the Sun’s parental molecular cloud changed over time. In this model, CAIs and AOAs record the isotopic composition of the early infall, while later-formed solids contain a larger fraction of the later, isotopically distinct infall. This model implies that CAIs and AOAs record the isotopic composition of the Sun and suggests that the nucleosynthetic isotope heterogeneity of the solar system is predominantly produced by mixing of solar nebula condensates, which acquired their distinct isotopic compositions as a result of time-varied infall from the protosolar cloud.

¹E. Dobrica,²K.A. McCain,³A.J. Brearley
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2024.01.017]
¹Hawai‘i Institute of Geophysics and Planetology, School of Ocean, Earth Science, and Technology, University of Hawai‘i at Mānoa, Honolulu, HI
²Jacobs Jets II Contract, NASA-Johnson Space Center, Houston, TX, USA
³Department of Earth and Planetary Sciences, MSC03-2040, 1University of New Mexico, Albuquerque, NM
Copyright Elsevier

We have investigated different carbonate minerals (calcite, aragonite, and ankerite) from two meteorites with different shock metamorphic stages (Boriskino, CM2 − ∼S3-S4 and Murchison CM2.5-2.2 − S1-S2) using various electron microscope techniques. Our detailed transmission electron microscopy study shows that carbonates are valuable recorders of the shock metamorphic environment and help interpret shock metamorphic conditions on the chondrite parent asteroids. We show the occurrence of fine-scale complex microstructures (dislocations, modulations, mosaic blocks, and microfractures) in all carbonates analyzed, indicating that they were modified during deformation processes at a variable degree. The presence of shock features in all generations of carbonates (Type 0, 1, and 2) indicates that shock deformation event/(s) occurred after the precipitation of all types of carbonates. In Boriskino, the most shocked meteorite analyzed, carbonates record very distinct microstructures compared to Murchison, an unshocked or very weakly shocked sample. We divided these microstructures into two different categories as a function of the degrees of deformation, and several features could be used as diagnostic tools for low and high shock pressures in meteorites. Deformation features are pervasive in calcites, aragonites (Type 1 and 2 Ca carbonates), and ankerites from Boriskino. However, the abundance and distribution of these deformation features are minimal in all calcite crystals analyzed from Murchison and one Type 0 Ca carbonate from Boriskino. This suggests the presence of a correlation between these microstructural features and the degree of shock metamorphic stages of the samples analyzed. The low amount of deformation features in the Type 0 calcite from Boriskino could indicate that the least altered lithologies from Boriskino were not subject to high-intensity impacts.

^1,2S. A. Singerling,³C. M. Corrigan,⁴A. J. Brearley
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.14132]
¹Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque, New Mexico, USA
²Department of Geosciences, Goethe University Frankfurt, Altenhoeferallee 1, 60438 Frankfurt am Main, Germany.
³Department of Mineral Sciences, National Museum of Natural History, Smithsonian Institution, Washington, DC, USA
⁴Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque, New Mexico, USA
Published by arrangement with John Wiley & Sons

We have carried out a SEM-EPMA-TEM study to determine the textures and compositions of relict primary iron sulfides and their alteration products in a suite of moderately to heavily altered CM1 carbonaceous chondrites. We observed four textural groups of altered primary iron sulfides: (1) pentlandite+phyllosilicate (2P) grains, characterized by pentlandite with submicron lenses of phyllosilicates; (2) pyrrhotite+pentlandite+magnetite (PPM) grains, characterized by pyrrhotite–pentlandite exsolution textures with magnetite veining and secondary pentlandite; (3) pentlandite+serpentine (PS) grains, characterized by relict pentlandite exsolution, serpentine, and secondary pentlandite; and (4) pyrrhotite+pentlandite+magnetite+serpentine (PPMS) grains, characterized by features of both the PPM and PS grains. We have determined that all four groups were initially primary iron sulfides, which formed from crystallization of immiscible sulfide melts within silicate chondrules in the solar nebula. The fact that such different alteration products could result from the same precursor sulfides within even the same meteorite sample further underscores the complexity of the aqueous alteration environment for the CM chondrites. The different alteration reactions for each textural group place constraints on the mechanisms and conditions of alteration with evidence for acidic environments, oxidizing environments, and changing fluid compositions (Ni-bearing and Si-Mg-bearing).

¹Ted M Johnson,¹Beth L. Klein,²D. Koester,³Carl Melis,¹B. Zuckerman,¹M. Jura
The Astrophysical Journal 941, 113 Open Access Link to Article [DOI 10.3847/1538-4357/aca089]
¹Department of Physics and Astronomy, University of California, Los Angeles, CA 90095-1562, USA; tedjohnson12@g.ucla.edu
²Institut fur Theoretische Physik und Astrophysik, University of Kiel, D-24098 Kiel, Germany
³Center for Astrophysics and Space Sciences, University of California, San Diego, CA 92093-0424, USA

Ultraviolet and optical spectra of the hydrogen-dominated atmosphere white dwarf star G238-44 obtained with FUSE, Keck/HIRES, HST/COS, and HST/STIS reveal 10 elements heavier than helium: C, N, O, Mg, Al, Si, P, S, Ca, and Fe. G238-44 is only the third white dwarf with nitrogen detected in its atmosphere from polluting planetary system material. Keck/HIRES data taken on 11 nights over 24 yr show no evidence for variation in the equivalent width of measured absorption lines, suggesting stable and continuous accretion from a circumstellar reservoir. From measured abundances and limits on other elements, we find an anomalous abundance pattern and evidence for the presence of metallic iron. If the pollution is from a single parent body, then it would have no known counterpart within the solar system. If we allow for two distinct parent bodies, then we can reproduce the observed abundances with a mix of iron-rich Mercury-like material and an analog of an icy Kuiper Belt object with a respective mass ratio of 1.7:1. Such compositionally disparate objects would provide chemical evidence for both rocky and icy bodies in an exoplanetary system and would be indicative of a planetary system so strongly perturbed that G238-44 is able to capture both asteroid and Kuiper Belt–analog bodies near-simultaneously within its <100 Myr cooling age.

^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.