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.