Recent near-Earth supernovae probed by global deposition of interstellar radioactive ⁶⁰Fe

The rate of supernovae (SNe) in our local galactic neighborhood within a distance of ~100 parsec from Earth (1 parsec (pc)=3.26 light years) is estimated at 1 SN every 2-4 million years (Myr), based on the total SN-rate in the Milky Way (2.0±0.7 per century). Recent massive-star and SN activity in Earth’s vicinity may be evidenced by traces of radionuclides with half-lives t_1/2 ≤ 100 Myr, if trapped in interstellar dust grains that penetrate the Solar System (SS). One such radionuclide is ⁶⁰Fe (t_1/2=2.6 Myr) which is ejected in supernova explosions and winds from massive stars. Here we report that the ⁶⁰Fe signal observed previously in deep-sea crusts, is global, extended in time and of interstellar origin from multiple events. Deep-sea archives from all major oceans were analyzed for ⁶⁰Fe deposition via accretion of interstellar dust particles. Our results, based on ⁶⁰Fe atom-counting at state-of-the-art sensitivity, reveal ⁶⁰Fe interstellar influxes onto Earth 1.7–3.2 Myr and 6.5–8.7 Myr ago. The measured signal implies that a few percent of fresh ⁶⁰Fe was captured in dust and deposited on Earth. Our findings indicate multiple supernova and massive-star events during the last ~10 Myr at nearby distances ≤100 pc.