Stardust in Antarctic ice reveals 80 years of solar system history

Hidden in the depths of Antarctic ice are traces of distant stellar explosions that help us understand how the Solar System traveled through interstellar clouds over tens of thousands of years.

Researchers from the Australian National University have released the results of an analysis of 300 kilograms of Antarctic ice dating back 40 to 80 years. The samples showed significantly lower levels of the radioactive isotope iron-60 than expected. The discovery suggests that the solar system passed through a less dense part of the local interstellar cloud during this time.

Interstellar clouds around us

There are about 15 separate interstellar clouds in our galaxy within the Local Complex. The solar system is currently moving through one of them, the Local Interstellar Cloud. These clouds are made up of gas, plasma, and tiny dust particles left over from the birth and death of stars. When massive stars explode as supernovae, they eject heavy elements, including the rare isotope iron-60, into space. These particles gradually settle to Earth and become embedded in ice sheets, forming a natural archive of cosmic events.

Antarctica is ideal for such studies: snow accumulates slowly and is almost undisturbed, preserving a sequence of layers for tens of thousands of years. Each layer records the composition of the atmosphere and cosmic dust at the time of its formation. That is why the scientists chose to analyze 500 kilograms of fresh snow and 300 kilograms of older ice.

How stardust was measured

The research process was extremely delicate. The ice was melted and then microscopic amounts of iron were chemically isolated. Then, using accelerator mass spectrometry at the Australian National University's Heavy Ion Accelerator, individual iron-60 atoms were counted. The level of deposition of the isotope was expected to remain stable, as in modern snow and ocean sediments several thousand years ago. However, the concentration in the older ice was noticeably lower.

This means that between 40 and 80 years ago, Earth received less interstellar dust. This change occurred over a relatively short timescale in astrophysics and is not related to ancient supernova explosions millions of years ago. Instead, everything points to local processes within the Local Interstellar Cloud.

The history of clouds and the movement of the solar system

Last year, astronomers reconstructed the origin of the Local Interstellar Cloud and concluded that it was most likely formed by a star exploding. They calculated that the solar system entered the Local Interstellar Cloud sometime between 40 and 124 years ago. This is when the iron-60 abundance should have changed, as confirmed by the Antarctic samples.

However, the story doesn't quite add up. If the clouds had formed directly from a supernova explosion, the levels of iron-60 would have been much higher. Instead, the scientists recorded moderate values, suggesting a more complex structure for the clouds—perhaps they went through several stages of mixing and rarefaction.

New data and prospects for 2026

In May 2026, the team expanded the study to include samples from depths that correspond to 120–150 years ago. Preliminary results show a gradual increase in iron-60 concentrations, which may indicate the time when the Solar System entered a denser part of the cloud. This data is consistent with models of the motion of stars in the Local Complex, published in the journal Astronomy & Astrophysics in March 2026.

Additional measurements from Greenland and high-altitude glaciers in Tibet confirm the general picture: the level of iron-60 fluctuates depending on the density of the interstellar medium. This allows us to create a three-dimensional map of the movement of the solar system through the clouds over the past 200 years.

Significance for understanding cosmic evolution

The discovery demonstrates that Earth is a natural detector of cosmic processes. Iron-60, with a half-life of 2,6 million years, serves as a precise clock for dating events. By combining geological archives with astronomical models, scientists have a unique opportunity to trace how supernova explosions affect the chemistry of the interstellar medium and, indirectly, planets.

In the coming years, deeper wells are planned in Antarctica to cover the period up to 300 years ago. This will allow us to find out whether there were previous entries of the solar system into other clouds and how this affected the level of cosmic radiation on Earth.