2023/07/15 by Desch, Steven J., Dunham, Emilie T., Herbst, Ashley K. +5 · 2 voices · 2 citations
#Earth and Planetary Astrophysics (astro-ph.EP) #FOS: Physical sciences #Geophysics (physics.geo-ph)
paper · doi:10.48550/arxiv.2307.07750
Most meteoritic calcium-rich, aluminum-rich inclusions (CAIs) formed from a reservoir with 26\rm Al/27\rm Al ≈ 5 × 10-5, but some record lower (26\rm Al/27\rm Al)0, demanding they sampled a reservoir without live 26\rm Al. 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-26\rm Al/27\rm Al 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 μ\rm m in size with no live 26\rm Al; live 26\rm Al 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 μ\rm m, even incorporating positively charged perovskite grains, but not the small, negatively charged 26\rm Al-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 48\rm Ca and 50\rm Ti anomalies (if carried by presolar perovskite) of LAACHIs, and especially how they incorporated no 26\rm Al in a solar nebula with uniform, canonical 26\rm Al/27\rm Al. A late injection of supernova material is obviated, although formation of the Sun in a high-mass star-forming region is demanded.