¹Steven J. Desch,^2,3Emilie T. Dunham,¹Ashley K. Herbst,⁴Cayman T. Unterborn,¹Thomas G. Sharp,¹Maitrayee Bose,⁵Prajkta Mane,⁶Curtis D. Williams
The Astrophysical Journal 953, 146 Open Access Link to Article [DOI 10.3847/1538-4357/acdeed]
¹School of Earth and Space Exploration, Arizona State University, P.O. Box 871404, Tempe, AZ 85287-1404, USA; steve.desch@asu.edu
²Department of Earth, Planetary and Space Sciences, University of California, Los Angeles, CA 90095, USA
³Department of Earth and Planetary Sciences, University of California, Santa Cruz, CA 95064, USA
⁴Southwest Research Institute, 6220 Culebra Road, San Antonio, TX 78238, USA
⁵Lunar and Planetary Institute, 3600 Bay Area Boulevard, Houston, TX 77058, USA
⁶Arctic Slope Regional Corporation Federal, 11091 Sunset Hills Road, Suite 800, Reston, VA 20190, USA

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