A rock sample dredged from the Pacific Ocean seafloor in 1976 has yielded extraordinary evidence of a violent cosmic event. Hidden within a ferromanganese crust are trace amounts of plutonium isotopes—elements forged in the collision of two neutron stars. The findings offer the strongest direct clues yet about the nature of such mergers and their role in seeding heavy elements across the universe.
The critical payload: just a few hundred atoms of plutonium radioisotopes. These isotopes decay at precise rates, allowing researchers to date the source event. The merger—a kilonova explosion—occurred more than 100 million years ago, showering nearby space with long-lived elements that eventually settled on Earth.
Material from the blast drifted through interstellar space and gradually accumulated on our planet. Some of it sank to the ocean floor, where it became trapped in the growing ferromanganese crust. That crust preserves a layered record of cosmic fallout over geologic timescales.
This discovery challenges assumptions about how frequently such rare stellar mergers occur and how their debris spreads. It also provides a new method for identifying past kilonovae by examining terrestrial rocks rather than relying solely on telescopic observations.
While the plutonium signature is compelling, some caution that the sample could have been contaminated by nuclear testing or industrial fallout over decades. Further analysis of additional deep-sea rocks will be needed to confirm the finding and rule out terrestrial sources.