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

Kohei Fukuda, Hajime Hiyagon, Wataru Fujiya, Naoto Takahata, Takanori Kagoshima, and Yuji Sano

The Astrophysical Journal, Volume 886, Number 1
Published 2019 November 15


“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.”