Evidence for a late supernova injection of ⁶⁰Fe into the protoplanetary disk

High-precision ⁶⁰Fe-⁶⁰Ni isotope data show that most meteorites originating from differentiated planetesimals that accreted within 1 million years of the solar system's formation have ⁶⁰Ni/ ⁵⁸Ni 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 ⁶⁰Fe. Evidence for live ⁶⁰Fe in younger objects suggests that ⁶⁰Fe was injected into the protoplanetary disk ∼1 million years after solar system formation, when ²⁶Al was already homogeneously distributed. Decoupling the first appearance of ²⁶Al and ⁶⁰Fe 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.