A rare radioactive isotope isolated from Antarctic ice has strengthened the case that the Solar System is currently moving through interstellar material seeded by an ancient stellar explosion.
By tracing iron-60 in ice deposited between 40,000 and 81,000 years ago, researchers found a lower influx than in younger Antarctic snow and marine sediments, a pattern consistent with Earth sampling a structured Local Interstellar Cloud rather than the fading aftermath of an older supernova.
The study builds on earlier detections of iron-60 in recent snow and deep-sea sediments, which hinted that the Local Interstellar Cloud might act as a long-lived reservoir for supernova debris. But those findings did not rule out other possibilities, including a slow decline from better-known supernova signals recorded millions of years ago. The new ice-core record extends that timeline into the interval when the Solar System may have been entering the cloud.
“Our idea was that the Local Interstellar Cloud contains iron-60 and can store it over long time periods,” said Dominik Koll in the team’s press release. “As the Solar System moves through the cloud, Earth could collect this material. However, we couldn’t prove this at the time.”
To test that idea, the team analyzed about 295 kilograms of EPICA Dronning Maud Land ice-core meltwater from Antarctica. To check that storage and chemical processing had not erased the signal, they first measured beryllium-10 and aluminum-26 at the DREAMS accelerator mass spectrometry facility in Dresden. Their expected abundances indicated that major losses were unlikely.
At the Heavy Ion Accelerator Facility in Canberra, the researchers then used accelerator mass spectrometry to count individual iron-60 atoms and compared them with manganese-53 using the ^60Fe/^53Mn ratio, a sensitive way to distinguish interstellar iron-60 from expected cosmogenic background in dust and meteorites.
Compared with recent Antarctic snow and Indian Ocean sediments, the ice-core record suggests that less iron-60 reached Earth between 40,000 and 80,000 years ago than in more recent times. The authors argue that this variable profile favors the Local Interstellar Cloud, or the wider cloud complex around it, over a simple long-term fade-out from older supernova ejecta.
“This means that the clouds surrounding the Solar System are linked to a stellar explosion,” said Koll. “And for the first time, this gives us the opportunity to investigate the origin of these clouds.”
The team now aims to push the record farther back, using older, high-resolution archives to trace the Solar System’s path through the surrounding interstellar environment in finer detail.
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