Deep below Antarctica, clues to an ancient puzzle with cosmic origins have remained trapped in the southernmost continent’s ice for tens of thousands of years—until now.
Researchers have unearthed new evidence of the presence of iron-60, a rare radioactive isotope of iron linked to stellar explosions, captured in Antarctic ice estimated to be up to 80,000 years old.
Because this rare iron isotope cannot form naturally on Earth under most circumstances, its origin is likely traced to the deaths of massive stars, in cataclysmic cosmic events that eject rare-Earth isotopes like iron-60 during supernova explosions.
Fortunately, this radioactive cosmic messenger, which has a half-life of around 2.6 million years, can be preserved following such large-scale cosmic events, becoming entombed in deep-sea sediments and in ice covering the surface of Antarctica.
The result is what scientists liken to the ancient cosmic “fingerprints” of past stellar cataclysms that can be traced all the way to Earth. The discovery was reported in a paper published in Physical Review Letters.
Fingerprints of the Cosmos in Antarctic Ice
Despite being one of the least-mapped surfaces in the entire Solar System by some estimates, over the last 35-million years, the accumulation of ice on Antarctica’s surface has slowly preserved a veritable “time capsule” of information about our planet’s geological past.
Accessing this deep geological history is as simple as drilling cores deep into Antarctica’s ice, which formed the basis of research led by German astrophysicist Dominik Koll, a researcher with the Helmholtz-Zentrum Dresden-Rossendorf, a Dresden-based research laboratory, which began in 2019.
However, the initial discoveries that prompted this research required no drilling at all—initial examination of fresh snow in Antarctica had already revealed the presence of iron-60, prompting a deeper search for past accumulations of this rare-Earth isotope.
Based on ice core analysis, additional signatures associated with stellar explosions have now been discovered deeper in our planet’s icy Antarctic archives, dating back to periods between around 40,000 and 81,000 years ago.
Interstellar Isotopes Below the Ice
Koll and his colleagues relied on samples collected in association with a research effort called the European Project for Ice Coring in Antarctica, or EPICA, in which portions of the ice cores were melted to reveal the presence of iron-60, which they counted atom-for-atom.
As they had hoped to find, a greater number of iron-60 atoms was present than would be expected based solely on background sources, meaning the rest is almost certainly of cosmic origin.
Intriguingly, the fact that far lower concentrations of iron-60 appeared to be present in ice from Earth’s long distant past, when compared to samples like those from fresh snow obtained by Koll and his team beginning in 2019, suggest that the region of space our Solar System is currently traversing, known as the Local Interstellar Cloud (LIC), is effectively “a cosmic archive for supernova-produced [iron-60].
Based on this, Koll and his colleagues report that the imprinted iron-60 profile over time points to strong evidence for changes in the local interstellar environment over the last 80,000 years, as represented in the EPICA ice samples.
Mysterious Origins of the Local Interstellar Cloud
Presently, astronomers are uncertain about the origins of the LIC, although the new findings suggest it has undergone significant changes over the last 100,000 years or so.
One thing that seems evident, based on the changes in the abundance of iron-60 throughout time, is that the LIC appears to have regions that possess more of it than others—very likely leftover from past stellar explosions.
Fundamentally, Koll and his colleagues say their recent findings align well with a supernova origin for the samples they uncovered, offering a unique opportunity to probe the ongoing mysteries of the LIC using relatively easily accessible ice cores from our planet’s southern continent.
The team’s findings were reported in a recent paper, “Local Interstellar Cloud structure imprinted in Antarctic ice by supernova 60Fe,” which appeared in Physical Review Letters.
Micah Hanks is the Editor-in-Chief and Co-Founder of The Debrief. A longtime reporter on science, defense, and technology with a focus on space and astronomy, he can be reached at micah@thedebrief.org. Follow him on X @MicahHanks, and at micahhanks.com.