Scientists have detected the radioactive isotope iron-60 in Antarctic ice cores, indicating that Earth and the Solar System have been moving through a cloud of supernova debris for at least 80,000 years.
"The ice core record provides a timeline of the Solar System's passage through the Local Interstellar Cloud."
Key Findings
- A team led by nuclear astrophysicist Dominik Koll of the Helmholtz-Zentrum Dresden-Rossendorf in Germany found iron-60 in ice cores dating from 40,000 to 81,000 years ago.
- Iron-60 is a radioactive isotope with a half-life of 2.6 million years. It is only formed in extreme stellar events such as supernova explosions and is not naturally produced on Earth in significant amounts.
- The concentration of iron-60 in older ice was significantly lower than in recent surface snow, suggesting the Solar System first entered a sparser region of the Local Interstellar Cloud and later moved into a denser region.
- The Local Interstellar Cloud is a region of gas, dust, and plasma that is believed to have been seeded by supernova activity.
Background
Previous studies had found iron-60 in Antarctic surface snow (2019) and ocean sediments. In this new work, the researchers analyzed 295 kg of Antarctic ice from the European Project for Ice Coring in Antarctica (EPICA) to isolate and count individual iron-60 atoms.
The iron-60 signal exceeds background contributions from cosmic rays, confirming an interstellar origin.
Implications
The findings support the hypothesis that the Local Interstellar Cloud has a heterogeneous structure, with varying densities of iron-60-bearing dust.
The research was published in Physical Review Letters.