(Credit: Paul Carroll on Unsplash)
In A Nutshell
- Scientists found traces of iron-60, a radioactive element linked to exploding stars, in Antarctic ice formed roughly 40,000 to 81,000 years ago.
- The amount detected was significantly lower than iron-60 levels found in more recent Antarctic snow and ocean sediment records, pointing to a changing interstellar environment over the last 80,000 years.
- The pattern fits with the idea that our solar system has been moving deeper into a nearby cloud of gas and dust that may be carrying remnants of ancient stellar explosions.
- The findings are suggestive, not conclusive: the signal came from just a handful of detected atoms, and alternative explanations have not been fully ruled out.
Buried deep in Antarctic ice formed tens of thousands of years ago, scientists have found traces of iron linked to stellar explosions. The pattern of those traces is now telling us something surprising about the invisible cloud of gas and dust our solar system is drifting through right now.
Researchers analyzed nearly 295 kilograms of ice drilled from Antarctica as part of the European Project for Ice Coring in Antarctica, a long-running international effort to extract climate and environmental records from deep ice. What they were hunting for wasn’t a climate signal. It was iron-60, a rare radioactive form of iron strongly associated with supernovae, though tiny amounts can also be made when cosmic rays hit material in space.
Finding it in ancient ice, far from any known recent stellar explosion, points to something intriguing: the cloud of gas and dust our solar system is currently drifting through may be acting like a kind of cosmic archive, carrying traces of material linked to earlier stellar explosions.
Our solar system is currently passing through what scientists call the Local Interstellar Cloud, one of roughly 15 warm, wispy pockets of gas and dust clustered in our corner of the galaxy. How this cloud and its neighbors formed remains one of astronomy’s open questions, with exploding stars among the leading suspects. If those explosions helped shape the cloud, ancient ice could hold the record of that contamination, layer by frozen layer.
Ice Drilled From Antarctica Yields Clues About Deep Space
To find these traces, the research team worked with ice from a core collected at the German Kohnen Station in Antarctica. Published in Physical Review Letters, the study analyzed ice representing a narrow slice of ancient time, roughly 40,000 to 81,000 years ago, chosen to capture what may have been the period just before or during our solar system’s entry into the Local Interstellar Cloud.
Detecting iron-60 in ice is not simple. Amounts involved are almost unimaginably small, and ordinary space rocks can muddy the signal. To get around that, the team compared iron-60 to a companion element called manganese-53. Both are produced by cosmic ray interactions at similar rates, so a surplus of iron-60 relative to manganese-53 suggests something beyond space rocks is responsible. That surplus showed up, though the signal is statistically limited, based on seven detector events compared to none in the background. Additional quality checks on the ice confirmed the sample hadn’t degraded during storage.
Ancient Ice Shows Supernova-Linked Iron Levels Were Once Far Lower
What makes this particularly compelling isn’t just the detection of iron-60. It’s how much was found, or rather, how little. The ancient ice showed a much lower deposition rate, about 0.22 iron-60 atoms per square centimeter per year, though with wide uncertainty because the signal came from only a handful of detected atoms. That rate is significantly lower than what has been detected in recent Antarctic surface snow and in deep-sea sediments from the Indian Ocean covering roughly the last 33,000 years.
The available records point to a higher iron-60 influx in more recent times, although the older ice sample covers too broad a window to show exactly when that change occurred. That pattern fits with the idea that our solar system has been gradually moving deeper into the Local Interstellar Cloud. If the cloud is carrying iron-60 left over from ancient stellar explosions, the solar system would have encountered less of it when it was on the outskirts, or perhaps still outside the cloud’s boundaries, tens of thousands of years ago.
What the Supernova Iron Signal Says About Our Location in the Galaxy
Scientists have previously found large spikes of iron-60 in ancient ocean sediments and rocky crusts roughly 2 to 3 million years old and about 7 million years old, likely from nearby supernovae. A lingering question has been whether the more modest recent signal is just a fading echo of those old blasts, or whether it reflects something more local.
New data favor the local cloud explanation, though other possibilities remain open. The pattern is harder to explain as a simple fading echo from the 2 to 3 million-year-old signal, because that scenario would require a more complicated structure in the Local Bubble. Reflections of older iron-60 off the Local Bubble’s boundary, or density variations within the cloud itself, also can’t be ruled out. The exact timing of the solar system’s entry into the Local Interstellar Cloud remains uncertain, with estimates ranging from roughly 40,000 to 124,000 years ago.
Looking ahead, the researchers suggest that studying ice or geological records beyond 100,000 years ago could trace the solar system’s broader journey through this region of the galaxy. Models suggest the solar system could exit the Local Interstellar Cloud entirely within the next 2,000 to 6,000 years. Antarctic ice, long prized as a climate archive, turns out to be capable of preserving something far more exotic. Faint chemical traces of events that unfolded long before humans walked the Earth have been sitting frozen at the bottom of the world, waiting to be read.
Paper Notes
Limitations
The study’s authors acknowledge several important uncertainties. The time window of 40,000 to 81,000 years ago is covered by a single bulk sample rather than a finely sliced time series, which limits the team’s ability to pinpoint exactly when the iron-60 deposition rate changed. The detection itself, based on seven detector events compared to none in the background measurement, carries significant statistical uncertainty, reflected in the wide error margins reported for the deposition rate. The exact timing of the solar system’s entry into the Local Interstellar Cloud remains poorly constrained in existing models, with estimates ranging from roughly 40,000 to 124,000 years ago, making it difficult to determine with precision whether the ice core period represents a time when the solar system was outside, entering, or already inside the cloud. Other possible explanations for the observed iron-60 signal, including reflections of older supernova debris off the boundary of the Local Bubble, or density variations within the cloud itself, cannot be fully ruled out with current data.
Funding and Disclosures
The work was supported in part by the Australian Government through the National Collaborative Research Infrastructure Strategy program. Research was also partially carried out at the Ion Beam Center at the Helmholtz-Zentrum Dresden-Rossendorf, a member of the Helmholtz Association, under Project No. 23003438-ST. This is listed as EPICA publication No. 327. Logistical support for fieldwork in Dronning Maud Land was provided by the Alfred Wegener Institute. One author was supported through the Helmholtz Association under grant VH-NG 1501. No competing interests or conflicts are disclosed.
Publication Details
Authors: 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. Institutions represented include Helmholtz-Zentrum Dresden-Rossendorf (Germany), The Australian National University (Australia), TUD Dresden University of Technology (Germany), University of Bonn (Germany), Alfred-Wegener-Institut Helmholtz-Zentrum für Polar- und Meeresforschung (Germany), University of Bremen (Germany), and University of Göttingen (Germany). The paper, titled “Local Interstellar Cloud Structure Imprinted in Antarctic Ice by Supernova ⁶⁰Fe,” was published May 13, 2026, in Physical Review Letters, Volume 136, Article 192701. DOI: 10.1103/nxjq-jwgp. The paper received an Editors’ Suggestion designation and was featured in Physics by the journal.
