Earth is flying through the radioactive ashes of an ancient exploded star, and Antarctic ice preserved the evidence.
Scientists have found new evidence that Earth is moving through a cloud of ancient supernova debris left behind by a long ago stellar explosion. By examining Antarctic ice tens of thousands of years old, researchers detected iron-60, a rare radioactive isotope created when massive stars explode. The findings suggest that the Local Interstellar Cloud surrounding our Solar System contains lingering material from an ancient supernova. The study was led by an international team from the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) and published in Physical Review Letters.
Ancient Supernova Material Reaching Earth
Iron-60 forms inside massive stars and is blasted into space during supernova explosions. Geological evidence has previously shown that Earth was exposed to iron-60 from nearby supernovae millions of years ago. In modern times, however, no nearby stellar explosions have occurred that could directly supply fresh iron-60.
That raised questions when scientists recently discovered traces of iron-60 in relatively young Antarctic snow.
“Our idea was that the Local Interstellar Cloud contains iron-60 and can store it over long time periods. As the Solar System moves through the cloud, Earth could collect this material. However, we couldn’t prove this at the time,” explains Dr. Dominik Koll from the Institute of Ion Beam Physics and Materials Research at HZDR.
Over the past several years, Koll and Prof. Anton Wallner analyzed additional samples, including deep sea sediments dating back as far as 30,000 years. Those samples also contained iron-60, but scientists still could not fully rule out competing explanations.
The newly studied Antarctic ice samples are between 40,000 and 80,000 years old. Researchers say the results now strongly indicate that the Local Interstellar Cloud is the source of the radioactive material.
“This means that the clouds surrounding the Solar System are linked to a stellar explosion. And for the first time, this gives us the opportunity to investigate the origin of these clouds,” says Koll.
Solar System Passing Through the Local Interstellar Cloud
Scientists believe the Solar System entered the Local Interstellar Cloud several tens of thousands of years ago and will exit it again in a few thousand years. Researchers say the Solar System is currently near the edge of the cloud.
To investigate the timing, the team analyzed an ice core covering the period when the Solar System may have first entered the cloud. The sample was provided by the Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research (AWI) through the European EPICA ice drilling project.
By comparing the Antarctic ice results with earlier snow and deep-sea sediment measurements, researchers found that Earth received less iron-60 between 40,000 and 80,000 years ago than it does today.
“This suggests that we were previously in a medium with lower iron-60 content, or that the cloud itself exhibits strong density variations,” explains Koll.
The team also found that the iron-60 signal changes over relatively short cosmic timescales, shifting noticeably over just tens of thousands of years. That allowed researchers to reject alternative theories, including the idea that the material was simply fading remnants from supernova explosions millions of years ago.
Antarctic Ice Reveals Radioactive Iron
To carry out the study, researchers transported about 300 kilograms of ice from AWI in Bremerhaven to Dresden for chemical analysis. After extensive processing, only a few hundred milligrams of dust remained.
Scientists then carefully isolated the iron-60 while working to avoid losing any material during preparation.
At the DREsden Accelerator Mass Spectrometry (DREAMS) laboratory at HZDR, the researchers tested the prepared samples using two other radioisotopes: beryllium-10 and aluminum-26. The expected concentrations of these isotopes in Antarctic ice are already well understood. If iron-60 had been lost during processing, the amounts of these isotopes would also have decreased. The team found no evidence of such losses.
Detecting Just a Few Atoms
For the final measurements, researchers used the Heavy Ion Accelerator Facility (HIAF) at the Australian National University, which is currently the only facility in the world capable of detecting such tiny amounts of iron-60. Electric and magnetic filters separated unwanted atoms by mass until only a handful of iron-60 atoms remained from an original sample containing 10 trillion atoms.
“It’s like searching for a needle in 50,000 football stadiums filled to the roof with hay. The machine finds the needle in an hour,” explains Annabel Rolofs from the University of Bonn.
“Through many years of collaboration with international colleagues, we have developed an extremely sensitive method that now allows us to detect the clear signature of cosmic explosions that occurred millions of years ago in geological archives today,” summarizes Wallner.
The research team is now planning additional studies using even older Antarctic ice cores that formed before the Solar System entered the Local Interstellar Cloud. AWI is also involved in the Beyond EPICA – Oldest Ice project, which aims to recover ice cores dating back even farther into Earth’s history.
Reference: “Local Interstellar Cloud Structure Imprinted in Antarctic Ice by Supernova” by Dominik Koll, Annabel Rolofs, Florian Adolphi, Sebastian Fichter, Maria Hoerhold, Johannes Lachner, Stefan Pavetich, Georg Rugel, Stephen Tims, Frank Wilhelms, Sebastian Zwickel and Anton Wallner, 13 May 2026, Physical Review Letters.
DOI: 10.1103/nxjq-jwgp
Never miss a breakthrough: Join the SciTechDaily newsletter.
Follow us on Google and Google News.