Scientists Find Iron-60 in 80,000-Year-Old Antarctic Ice as Stardust Still Reaches Earth

Q: Supernova explosions happened millions of years ago. Why is their radioactive dust only reaching Earth now?

Because the dust travels far more slowly than light and can linger for millions of years in interstellar clouds before Earth encounters it. The supernovae that made iron-60 likely exploded 15 to 20 million years ago. Their light would have passed Earth long ago, but the physical debris moved outward much more slowly, mixing into the interstellar medium rather than arriving in one quick wave. Scientists think much of that material became part of the Local Interstellar Cloud, a nearby patch of gas and dust shaped by past supernova activity. The key point is that the solar system is moving. Evidence from Antarctic ice, deep-sea sediments and NASA’s ACE spacecraft suggests Earth has been passing through this supernova-enriched cloud for tens of thousands of years, and may still be doing so. As the solar system crosses denser or thinner parts of that cloud, the amount of iron-60 reaching Earth changes. That helps explain why researchers found iron-60 in ice layers only 40,000 to 80,000 years old even though the explosions were much older. The dust was not “late” in a simple sense; it was stored and redistributed in the local interstellar environment, then swept up as Earth moved through it. Scientists say this makes iron-60 a useful fingerprint of ancient nearby supernovae and of the changing cosmic environment around the solar system.

3 articles · Updated · The Economic Times · Jun 16

Antarctic ice layers dating 40,000 to 80,000 years old contained traces of iron-60, giving fresh evidence that radioactive debris from ancient supernovae is still falling to Earth.
Iron-60 forms in massive stars and is blasted out in stellar explosions, making it a distinctive marker scientists can use to trace past supernova activity near the solar system.
Nearly 300 kilograms of ice had to be processed to isolate only a handful of atoms, underscoring how rare the material is and why the detection required specialized instruments.
The finding matches earlier iron-60 evidence in million-year-old deposits and NASA ACE observations near Earth, while the varying levels suggest the solar system may have moved through regions with different dust densities.