Some heavy elements such as iron, potassium, and iodine, created in star explosions, or supernovae, are vital for human life. It is believed that heavier elements like gold, uranium, and plutonium were formed from a more violent event, such as two neutron stars merging.
But, a new study suggests a more complex picture. The Australian National University (ANU) study reported the first-ever discovery of an extraterrestrial radioactive isotope on Earth.
The study was conducted in collaboration with the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) and Technical University Dresden in Germany and researchers from Australia, Israel, Japan, Switzerland, and Germany.
Scientists have discovered tiny traces of plutonium-244 in ocean crust alongside radioactive iron-60. Both isotopes are evidence of violent cosmic events in the proximity of Earth millions of years ago.
Professor Anton Wallner from The Australian National University (ANU) said, “The story is complicated—possibly this plutonium-244 was produced in supernova explosions, or it could be leftover from a much older, but even more spectacular event such as a neutron star detonation.”
Any plutonium-244 and iron-60 existed when the Earth shaped from interstellar gas and dust more than four billion years ago has since a long time ago decayed, so current traces of them probably originated from recent cosmic events in space.
When scientists dated the samples, they confirmed that two or more supernova explosions occurred near Earth.
Professor Wallner said, “Our data could be the first evidence that supernovae do indeed produce plutonium-244. Or perhaps it was already in the interstellar medium before the supernova went off, and it was pushed across the solar system together with the supernova ejecta.”
- A. Wallner et al. 60Fe and 244Pu deposited on Earth constrain the r-process yields of recent nearby supernovae, Science (2021). DOI: 10.1126/science.aax3972
- Daniel Clery. Trace seabed plutonium points to stellar forges of heavy elements, Science (2021). DOI: 10.1126/science.abj4596