Stardust From Supernova Explosion That Rained Iron Particles Down on Earth Discovered in Antarctic Snow

Scientists say they have discovered "stardust" in Antarctic snow originating from a supernova explosion that showered the Earth in particles of an unusual type of iron.

Our planet is constantly being bombarded with extraterrestrial dust. But now the researchers have reported the "very first detection of a recent influx" of the isotope iron-60 onto Earth, according to a study published in the journal Physical Review Letters.

The team led by Dominik Koll—a physicist from the Australian National University—examined the possibility that the iron-60 could have come from terrestrial sources, but they eventually concluded that it must be interstellar in origin, likely coming from a supernova in the neighborhood of our Sun.

For the study, the researchers took samples of fresh snow from Antarctica and melted it in order to analyze the particles that remained.

"We collected 500 kilograms [1,100 pounds] of surface snow in Antarctica, shipped it to Munich in a frozen state, melted and filtered it and did some chemistry on the filters and on the water," Koll told Newsweek. "The measurement of iron-60 was then done at the accelerator lab in Garching, Germany with accelerator mass spectrometry—that's single atom counting."

They found that the snow contained substantial quantities of dust-enriched with iron-60—which isn't naturally produced on our planet—that had accumulated over the past two decades or so. This rare substance is an isotope of the element iron—a chemical variant with atoms that contain a different number of neutrons, (in this case, four more than standard iron.)

This radioactive isotope has a half-life of around 2.6 million years, which essentially means that this is the time it takes for one-half of the atomic nuclei in a sample of the substance to decay. In other words, it is very long-lasting compared to many other radioactive molecules with short half-lives, enabling scientists to detect it.

The researchers say that only aging, massive stars in their death throes and certain types of supernova explosions can produce heavy metals such as iron-60, spewing particles of these substances into space.

In fact, a star has to be tens of times more massive than our Sun to be capable of creating iron isotopes, indicating that the iron-60 originated from outside of the solar system.

"It must have been a supernova, not so near as to kill us but not too far to be diluted in space," Koll said in a statement.

This conclusion led Koll to suggest that our planet was showered with the iron-60 particles at some point in our solar system's travels through a region of our galaxy known as the Local Interstellar Cloud. This region—which spans about 30 light-years across—is thought to have formed after massive stars exploded as supernovae, ejecting vast quantities of gas into space.

However, it is not clear exactly where the iron-60 came from. Koll said that further research is required to pinpoint the precise origin of the stardust.

While iron-60 is not produced naturally on Earth, the scientists had to rule out the possibility that the material they collected could have been produced by nuclear weapons tests or nuclear power plants. The large amount of the substance that they found was sufficient to dismiss this hypothesis given that man-made nuclear activities could only have produced a tiny quantity, according to their calculations.

Bernhard Peucker-Ehrenbrink, a geochemist at Woods Hole Oceanographic Institution, who was not involved in the study, praised the team's work for detecting substantial amounts of iron-60, originating from outside the solar system.

"Making these measurements is very difficult," he said. "You're essentially counting individual atoms. Extracting that from half a ton of ice is not a trivial undertaking."

This article was updated to include additional comments from Dominik Koll.