⁶⁰Fe and ²⁶Al in chondrules from unequilibrated chondrites: implications for early Solar System processes

Abstract

The presence of about a dozen short-lived nuclides in the early solar system, including ⁶⁰Fe and ²⁶Al, has been established from isotopic studies of meteorite samples. An accurate estimation of solar system initial abundance of ⁶⁰Fe, a distinct product of stellar nucleosynthesis, is important to infer the stellar source of this nuclide. Previous studies in this regard suffered from the lack of exact knowledge of the time of formation of the analyzed meteorite samples. We present here results obtained from the first combined study of ⁶⁰Fe and ²⁶Al records in early solar system objects to remove this ambiguity. Chondrules from unequilibrated ordinary chondrites belonging to low petrologic grades were analyzed for their Fe-Ni and Al-Mg isotope systematics. The Al-Mg isotope data provide the time of formation of the analyzed chondrules relative to the first solar system solids, the Ca-Al-rich inclusions. The inferred initial ⁶⁰Fe/⁵⁶Fe values of four chondrules, combined with their time of formation based on Al-Mg isotope data, yielded a weighted mean value of (6.3 ± 2) × 10^-7 for solar system initial ⁶⁰Fe/⁵⁶Fe. This argues for a high-mass supernova as the source of ⁶⁰Fe along with ²⁶Al and several other short-lived nuclides present in the early solar system.