Evidence for a Late Supernova Injection of 60 Fe into the Protoplanetary Disk

Abstract

High-precision 60 Fe- 60 Ni isotope data show that most meteorites originating from differentiated planetesimals that accreted within 1 million years of the solar system's formation have 60 Ni/ 58 Ni ratios that are ∼25 parts per million lower than samples from Earth, Mars, and chondrite parent bodies. This difference indicates that the oldest solar system planetesimals formed in the absence of 60 Fe. Evidence for live 60 Fe in younger objects suggests that 60 Fe was injected into the protoplanetary disk ∼1 million years after solar system formation, when 26 Al was already homogeneously distributed. Decoupling the first appearance of 26 Al and 60 Fe constrains the environment where the Sun's formation could have taken place, indicating that it occurred in a dense stellar cluster in association with numerous massive stars.