Iron 60 evidence for early injection and efficient mixing of stellar debris in the protosolar nebula

Abstract

Among extinct radioactivities present in meteorites, ⁶⁰Fe (t<inf>1/2</inf> = 1.49 Myr) plays a key role as a high-resolution chronometer, a heat source in planetesimals, and a fingerprint of the astrophysical setting of solar system formation. A critical issue with ⁶⁰Fe is that it could have been heterogeneously distributed in the protoplanetary disk, calling into question the efficiency of mixing in the solar nebula or the timing of ⁶⁰Fe injection relative to planetesimal formation. If this were the case, one would expect meteorites that did not incorporate ⁶⁰Fe (either because of late injection or incomplete mixing) to show ⁶⁰Ni deficits (from lack of ⁶⁰Fe decay) and collateral effects on other neutron-rich isotopes of Fe and Ni (coproduced with ⁶⁰Fe in core-collapse supernovae and AGB stars). Here, we show that measured iron meteorites and chondrites have Fe and Ni isotopic compositions identical to Earth. This demonstrates that ⁶⁰Fe must have been injected into the protosolar nebula and mixed to less than 10% heterogeneity before formation of planetary bodies. © 2008. The American Astronomical Society. All rights reserved.