Atomic-scale structure and non-stoichiometry of meteoritic hibonite: A transmission electron microscope study

Han, J.; Yasuhara, Akira; Keller, L. P.

doi:10.2138/am-2022-8014

Cited by 5 publications

(1 citation statement)

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“…Hibonite formed from a combination of presolar corundum and presolar spinel would be a mixture of subparallel platy crystals like those found in PLACs, and finer randomly oriented hibonites. Excess Al 2 O 3 from incomplete transformation would likely include stacking defects consisting of excess spinel-like layers (Han et al 2015(Han et al , 2022 as well as corundum inclusions.…”

Section: Mineralogy and Microstructuresmentioning

confidence: 99%

Origin of Low-26Al/27Al Corundum/Hibonite Inclusions in Meteorites

Desch

Dunham

Herbst

et al. 2023

ApJ

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Most meteoritic calcium-rich, aluminum-rich inclusions formed from a reservoir with 26Al/27Al ≈ 5 × 10−5, but some record lower ( 26 Al / 27 Al ) 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 1–103 μm, 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.

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Section: Mineralogy and Microstructuresmentioning

confidence: 99%