Origin of the Short-lived Radionuclide 10Be and Its Implications for the Astronomical Setting of CAI Formation in the Solar Protoplanetary Disk

• Published in: The Astrophysical journal Vol. 886; no. 1
• Main Authors: Fukuda, Kohei, Hiyagon, Hajime, Fujiya, Wataru, Takahata, Naoto, Kagoshima, Takanori, Sano, Yuji
• Format: Journal Article
• Language: English
• Published: Philadelphia The American Astronomical Society 15.11.2019; IOP Publishing
• Subjects: Aluminum; Astronomy; Astrophysics; Beryllium; Beryllium 10; Beryllium 9; Calcium-aluminum-rich inclusions; Carbonaceous chondrites; Celestial bodies; Chondrites; Composition; Fluxes; Irradiation; Isotope composition; Isotopes; Lithium; Magnesium; meteorites, meteors, meteoroids; nuclear reactions, nucleosynthesis, abundances; Protoplanetary disks; Radioisotopes; Solar composition; Solar cosmic rays; Solar system; Sun: abundances
• ISSN: 0004-637X; 1538-4357
• DOI: 10.3847/1538-4357/ab479c

We report Li-Be-B and Al-Mg isotopic compositions of Ca-Al-rich inclusions (CAIs) in Sayh al Uhaymir 290 (CH) and Isheyevo (CH/CB) metal-rich carbonaceous chondrites. All CAIs studied here do not show resolvable excesses in 26Mg, a decay product of the short-lived radionuclide 26Al, which suggests their formation occurred prior to the injection of 26Al into the solar system from a nearby stellar source. The inferred initial 10Be/9Be ratios obtained for these CAIs range from 0.17 × 10−3 to 6.1 × 10−3, which tend to be much higher and more variable than those of CAIs in CV3 chondrites. The high 10Be/9Be ratios suggest that 10Be was most likely synthesized through solar cosmic-ray irradiation. The lithium isotopic compositions of these CAIs are nearly chondritic, independent of their initial 10Be/9Be ratios. This can be explained by the irradiation targets being of chondritic composition; in other words, targets were most likely not solid CAI themselves, but their precursors in solar composition. The larger variations in 10Be/9Be ratios observed in CH and CH/CB CAIs than in CV CAIs may reflect more variable cosmic-ray fluxes from the earlier, more active Sun at an earlier evolutionary stage (class 0-I) for the former, and a later, less active stage of the Sun (class II) for the latter. If this is the case, our new Be-B and Al-Mg data set implies that the earliest formed CAIs tend to be transported into the outer part of the solar protoplanetary disk, where the parent bodies of metal-rich chondrites likely accreted.