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

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