A rock sample retrieved from the Pacific Ocean floor in 1976 is providing scientists with fresh evidence of a cosmic event that took place roughly 100 million years ago. Researchers have identified plutonium isotopes in the ferromanganese rock, elements that can only be forged in extremely energetic astrophysical processes.
Origin of the Plutonium Isotopes
About 100 million years ago, two neutron stars collided in a cataclysmic event known as a kilonova. The explosion expelled heavy elements, including long‑lived plutonium isotopes, into space. This stellar debris spread throughout the solar system and eventually settled onto Earth.
How the Rock Preserves the Cosmic Record
A fraction of the debris sank to the ocean floor and became incorporated into sedimentary deposits. Over time, a ferromanganese nodule formed, trapping several hundred atoms of radioactive plutonium within its matrix. Analyzing these atoms allows scientists to infer details about the merger and its timing.
Implications for Astrophysics
The identified plutonium isotopes constitute some of the strongest evidence that kilonovae are responsible for creating the heaviest elements in the universe. By measuring the ratios of different isotopes, researchers can narrow down the age of the collision.
Future Research Directions
Teams plan to examine additional oceanic rock samples to assess how common such events were and to refine nucleosynthesis models for kilonovae.