¹Peter Hoppe,^1,2Jan Leitner,^3,4,5Marco Pignatari,^6,7Sachiko Amari
The Astrophysical Journal Letters 943, L22 Open Access Link to Article [DOI 10.3847/2041-8213/acb157]
¹Max Planck Institute for Chemistry, Hahn-Meitner-Weg 1, D-55128 Mainz, Germany; peter.hoppe@mpic.de
²Institute of Earth Sciences, Heidelberg University, Im Neuenheimer Feld 234-236, D-69120 Heidelberg, Germany
³Konkoly Observatory, Konkoly Thege Miklos ut 15-17, 1121, Budapest, Hungary
⁴E. A. Milne Centre for Astrophysics, University of Hull, HU6 7RX, Hull, UK
⁵NuGrid Collaboration, USA 8
⁶McDonnell Center for the Space Sciences and Physics Department, Washington University, St. Louis, MO 63130, USA
⁷Geochemical Research Center, The University of Tokyo, Tokyo, 113-0033, Japan

We report C, N, Mg-Al, Si, and S isotope data of six 1–3 μm-sized SiC grains of Type X from the Murchison CM2 chondrite, believed to have formed in the ejecta of core-collapse supernova (CCSN) explosions. Their C, N, and Si isotopic compositions are fully compatible with previously studied X grains. Magnesium is essentially monoisotopic ²⁶Mg which gives clear evidence for the decay of radioactive ²⁶Al. Inferred initial ²⁶Al/²⁷Al ratios are between 0.6 and 0.78 which is at the upper end of previously observed ratios of X grains. Contamination with terrestrial or solar system Al apparently is low or absent, which makes the X grains from this study particularly interesting and useful for a quantitative comparison of Al isotope data with predictions from supernova models. The consistently high ²⁶Al/²⁷Al ratios observed here may suggest that the lower ²⁶Al/²⁷Al ratios of many X grains from the literature are the result of significant Al contamination and in part also of an improper quantification of ²⁶Al. The real dispersion of ²⁶Al/²⁷Al ratios in X grains needs to be explored by future studies. The high observed ²⁶Al/²⁷Al ratios in this work provide a crucial constraint for the production of ²⁶Al in CCSN models. We explored different CCSN models, including both “classical” and H ingestion CCSN models. It is found that the classical models cannot account for the high ²⁶Al/²⁷Al ratios observed here; in contrast, H ingestion models are able to reproduce the ²⁶Al/²⁷Al ratios along with C, N, and Si isotopic ratios reasonably well.

¹Yuki Hibiya,²Tsuyoshi Iizuka,²Hatsuki Enomoto,³Takehito Hayakawa
The Astrophysical Journal Letters 942, L15 Open Access Link to Article [DOI 10.3847/2041-8213/acab5d]
¹Research Center for Advanced Science and Technology, The University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8904
²Department of Earth and Planetary Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
¹National Institutes for Quantum Science and Technology, 2-4 Shirakata, Tokai, Naka, Ibaraki 319-1106, Japan

The short-lived radionuclide, niobium-92 (⁹²Nb), has been used to estimate the site of nucleosynthesis for p-nuclei and the timing of planetary differentiation, assuming that it was uniformly distributed in the early solar system. Here, we present the internal niobium–zirconium (Nb–Zr) isochron dating of Northwest Africa (NWA) 6704, an achondrite thought to form in the outer protosolar disk due to nucleosynthetic isotope similarities with carbonaceous chondrites. The isochron defines an initial ⁹²Nb/⁹³Nb ratio of (2.72 ± 0.25) × 10⁻⁵ at the NWA 6704 formation, 4562.76 ± 0.30 million years ago. This corresponds to a ⁹²Nb/⁹³Nb ratio of (2.96 ± 0.27) × 10⁻⁵ at the time of solar system formation, which is ∼80% higher than the values obtained from meteorites formed in the inner disk. The results suggest that a significant proportion of the solar ⁹²Nb was produced by a nearby core-collapse supernova (CCSN) and that the outer disk was more enriched in CCSN ejecta, which could account for the heterogeneity of short-lived ²⁶Al and nucleosynthetic stable-isotope anomalies across the disk. We propose that NWA 6704 serves as the best anchor for mapping relative Nb–Zr ages of objects in the outer solar system onto the absolute timescale.

¹J. N. Connelly,¹J. Bollard,¹E. Amsellem,¹M. Schiller,¹K. K. Larsen,¹M. Bizzarro
The Astrophysical Journal Letters 952, L33 Open Access Link to Article [DOI 10.3847/2041-8213/ace42e]
¹Centre for Star and Planet Formation, Globe Institute, University of Copenhagen, Øster Voldgade 5–7, DK-1350, Copenhagen, Denmark; connelly@sund.ku.dk

We present a U-corrected Pb–Pb age of 4566.19 ± 0.20 Ma (1.11 ± 0.26 Myr after t₀) for the moderately volatile element rich, andesitic meteorite Erg Chech 002 (EC002). Our Al–Mg isochron defines a ²⁶Al/²⁷Al initial ratio of (8.65 ± 0.09) × 10⁻⁶ that corresponds to a ²⁶Al/²⁷Al ratio of 2.48−0.56+0.67 × 10⁻⁵ for the parent body precursor at the time of solar system formation. Whereas the published bulk chemistry and our high-precision Ca isotope measurement correspond to those for inner solar system materials, the ²⁶Al/²⁷Al ratio overlaps that for outer solar system CI chondrites. This indicates that the carriers and/or processes responsible for the nucleosynthetic isotope compositions for inner and outer disk materials are different than those controlling the heterogeneous distribution of ²⁶Al. A low μ²⁶Mg* initial value of −6.1 ± 1.7 ppm infers a source region with a subchondritic Al/Mg ratio until 1.1 Myr after t₀ such that melt generation must have immediately preceded its crystallization. With ²⁶Al as the main heating source, a modeled temperature–time path for a 100 km radius parent body with our inferred ²⁶Al abundance suggests that accretion must have occurred before 0.5 Myr after t₀ to reach melting temperatures at appropriate depths within 1.1 Myr. This requires that the parent body formed very early within the protoplanetary disk, consistent with predictions of rapid formation of planetesimals by streaming instabilities within high-density dust filaments during the earliest phase of the protoplanetary disk. Finally, an absence of initial Pb in this otherwise moderately volatile-rich achondrite implies Pb was effectively sequestered to the Fe–Ni core.

¹C. Koike, ¹H. Chihara
The Astrophysical Journal 951, 24 Open Access Link to Article [DOI 10.3847/1538-4357/acd002]
¹Department of Environmental Science and Technology, Faculty of Design Technology, Osaka Sangyo University, 3-1-1 Nakagaito, Daito, Osaka 574-8530, Japan koike-c@mua.biglobe.ne.jp

The presence of amorphous silicate particles in interstellar and circumstellar space has been suggested based on the observation of 9.7 and 18 μm emission bands. We have successfully synthesized amorphous silicate samples of an enstatite and forsterite composition by the mechanical milling of mixed powder consisting of SiO2–MgO and SiO2–Mg(OH)2 reagent-grade particles under different rotation frequencies and milling times. These two types of starting materials are prepared to study the effect of the OH bond on synthesis and crystallization. The amorphous samples were characterized by X-ray diffraction and infrared spectroscopy. Amorphous samples with enstatite composition are synthesized from both SiO2–MgO and SiO2–Mg(OH)2 at 300 rpm and for 300 hr. Amorphous samples with forsterite composition are synthesized from both SiO2–MgO and SiO2–Mg(OH)2. The samples from SiO2–Mg(OH)2 require 400 rpm and a long milling time of 1600 hr. After crystallization, amorphous samples with an enstatite composition synthesized from SiO2–Mg(OH)2 mainly transform into forsterite with small amounts of amorphous silica SiO2 and enstatite depending on the rotation frequencies and milling time, while those from SiO2–MgO become enstatite. The amorphous samples with a forsterite composition are crystallized to forsterite from both starting materials. The presence of H2O or OH bonds significantly affects the final products after the crystallization of amorphous silicates of enstatite composition.

¹Zhang, Guozhuo,¹Wang, Xu,¹Wang, Yun,¹Cui, Han,¹Zhao, Weiqian,¹Qiu, Lirong
Measurement: Journal of the International Measurement Confederation 224, 113807 Link to Article [DOI 10.1016/j.measurement.2023.113807]
¹MIIT Key Laboratory of Complex-field Intelligent Exploration, School of Optics and Photonics, Beijing Institute of Technology, Beijing, 100081, China

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¹Kuwahara, Hideharu
Physics of the Earth and Planetary Interiors 346, 107123, Link to Article [DOI10.1016/j.pepi.2023.107123]
¹Geodynamics Research Center, Ehime University, Ehime, Japan

We currently do not have a copyright agreement with this publisher and cannot display the abstract here

¹Laurette Piani et al. (>10)
The Astrophysical Journal Letters 946, L43 Open Access Link to Article [DOI 10.3847/2041-8213/acc393]
¹Centre de Recherches Pétrographiques et Géochimiques, CNRS—Université de Lorraine; F-54500 Nancy, France

Rock fragments of the Cb-type asteroid Ryugu returned to Earth by the JAXA Hayabusa2 mission share mineralogical, chemical, and isotopic properties with the Ivuna-type (CI) carbonaceous chondrites. Similar to CI chondrites, these fragments underwent extensive aqueous alteration and consist predominantly of hydrous minerals likely formed in the presence of liquid water on the Ryugu parent asteroid. Here we present an in situ analytical survey performed by secondary ion mass spectrometry from which we have estimated the D/H ratio of Ryugu’s hydrous minerals, D/HRyugu, to be [165 ± 19] × 10−6, which corresponds to δDRyugu = +59 ± 121‰ (2σ). The hydrous mineral D/HRyugu’s values for the two sampling sites on Ryugu are similar; they are also similar to the estimated D/H ratio of hydrous minerals in the CI chondrites Orgueil and Alais. This result reinforces a link between Ryugu and CI chondrites and an inference that Ryugu’s samples, which avoided terrestrial contamination, are our best proxy to estimate the composition of water at the origin of hydrous minerals in CI-like material. Based on this data and recent literature studies, the contribution of CI chondrites to the hydrogen of Earth’s surficial reservoirs is evaluated to be ∼3%. We conclude that the water responsible for the alteration of Ryugu’s rocks was derived from water ice precursors inherited from the interstellar medium; the ice partially re-equilibrated its hydrogen with the nebular H2 before being accreted on the Ryugu’s parent asteroid.

^1,2Jonas M. Schneider,^1,2Christoph Burkhardt,^1,2 Thorsten Kleine
The Astrophysical Journal Letters 952, 1 Open Access Link to Article [DOI 10.3847/2041-8213/ace187]
¹Max Planck Institute for Solar System Research, Justus-von-Liebig-Weg 3, D-37077 Göttingen, Germany
²Institute for Planetology, University of Münster, Wilhelm-Klemm-Straße 10, D-48149 Münster, Germany

Nucleosynthetic isotope anomalies in meteorites allow distinguishing between the noncarbonaceous (NC) and carbonaceous (CC) meteorite reservoirs and show that correlated isotope anomalies exist in both reservoirs. It is debated, however, whether these anomalies reflect thermal processing of presolar dust in the disk or are primordial heterogeneities inherited from the solar system’s parental molecular cloud. Here, using new high-precision 84Sr isotope data, we show that NC meteorites, Mars, and the Earth and Moon are characterized by the same 84Sr isotopic composition. This 84Sr homogeneity of the inner solar system contrasts with the well-resolved and correlated isotope anomalies among NC meteorites observed for other elements, and most likely reflects correlated s- and (r, p)-process heterogeneities leading to 84Sr excesses and deficits of similar magnitude, which cancel each other out. For the same reason there is no clearly resolved 84Sr difference between NC and CC meteorites, because in some carbonaceous chondrites the characteristic 84Sr excess of the CC reservoir is counterbalanced by an 84Sr deficit resulting from s-process variations. Nevertheless, most carbonaceous chondrites exhibit 84Sr excesses, which reflect admixture of refractory inclusions and more pronounced s-process heterogeneities in these samples. Together, the correlated variation of s- and (r, p)-process nuclides revealed by the 84Sr data of this study refute an origin of these isotope anomalies solely by processing of presolar dust grains, but points to primordial mixing of isotopically distinct dust reservoirs as the dominant process producing the isotopic heterogeneity of the solar system.

^1,2Jan L. Hellmann,^1,3Jonas M. Schneider,^1,3Elias Wölfer,³Joanna Drążkowska,¹Christian A. Jansen,^1,3Timo Hopp,^1,3Christoph Burkhardt,^1,3Thorsten Kleine
The Astrophysical Journal 946, L34 Open Access Link to Article [DOI 10.3847/2041-8213/acc102]
¹Institut für Planetologie, University of Münster, Wilhelm-Klemm-Str. 10, D-48149 Münster, Germany;
²Department of Geology, University of Maryland, 8000 Regents Drive, College Park, MD 20742, USA
³Max Planck Institute for Solar System Research, Justus-von-Liebig-Weg 3, D-37077 Göttingen, Germany

Carbonaceous chondrites are some of the most primitive meteorites and derive from planetesimals that formed a few million years after the beginning of the solar system. Here, using new and previously published Cr, Ti, and Te isotopic data, we show that carbonaceous chondrites exhibit correlated isotopic variations that can be accounted for by mixing among three major constituents having distinct isotopic compositions, namely refractory inclusions, chondrules, and CI chondrite-like matrix. The abundances of refractory inclusions and chondrules are coupled and systematically decrease with increasing amount of matrix. We propose that these correlated abundance variations reflect trapping of chondrule precursors, including refractory inclusions, in a pressure maximum in the disk, which is likely related to the water ice line and the ultimate formation location of Jupiter. The variable abundance of refractory inclusions/chondrules relative to matrix is the result of their distinct aerodynamical properties resulting in differential delivery rates and their preferential incorporation into chondrite parent bodies during the streaming instability, consistent with the early formation of matrix-poor and the later accretion of matrix-rich carbonaceous chondrites. Our results suggest that chondrules formed locally from isotopically heterogeneous dust aggregates, which themselves derive from a wide area of the disk, implying that dust enrichment in a pressure trap was an important step to facilitate the accretion of carbonaceous chondrite parent bodies or, more generally, planetesimals in the outer solar system.

¹Ryan C. Ogliore
Geochemistry (Chemie der Erde) (in Press) Link to Article [https://doi.org/10.1016/j.chemer.2023.126046]
¹McDonnell Center for the Space Sciences, Washington University in St. Louis, 1 Brookings Dr., St. Louis 63130, MO, USA
Copyright Elsevier

NASA’s Stardust mission returned rocky material from the coma of comet 81P/Wild 2 (pronounced “Vilt 2”) to Earth for laboratory study on January 15, 2006. Comet Wild 2 contains volatile ices and likely accreted beyond the orbit of Neptune. It was expected that the Wild 2 samples would contain abundant primordial molecular cloud material—interstellar and circumstellar grains. Instead, the interstellar component of Wild 2 was found to be very minor, and nearly all of the returned particles formed in broad and diverse regions of the solar nebula. While some characteristics of the Wild 2 material are similar to primitive chondrites, its compositional diversity testifies to a very different origin and evolution history than asteroids. Comet Wild 2 does not exist on a continuum with known asteroids. Collisional debris from asteroids is mostly absent in Wild 2, and it likely accreted dust from the outer and inner Solar System (across the putative gap created by a forming Jupiter) before dispersal of the solar nebula. Comets are a diverse set of bodies, and Wild 2 may represent a type of comet that accreted a high fraction of dust processed in the young Solar System.