Antarctic Ice Reveals Earth May Be Traveling Through Ancient Supernova Dust
Tiny traces of a dead star could be falling to Earth right now. Researchers studying ancient Antarctic ice say our planet continues to pick up iron-60, a radioactive form of iron linked to supernova explosions. The material likely comes from the local interstellar cloud, a huge, thin cloud of gas and dust drifting between stars that the solar system has passed through for tens of thousands of years.
To investigate, the researchers analyzed Antarctic ice dating back 40,000 to 80,000 years. They found that the older ice contained less iron-60 than the newer samples, indicating that Earth moves through changing concentrations of material as it passes through the cloud. The results were published in Physical Examination Letters.
“This means that the clouds surrounding the solar system are linked to a stellar explosion. And for the first time, it gives us the opportunity to study the origin of these clouds,” said research leader Dominik Koll in a press release.
Learn more: Antarctica has a huge gravitational hole – and it dates back 70 million years
Earth could travel through ancient supernova material
The path of the solar system through the local interstellar cloud
(Image credit: B. Schröder/HZDR/NASA/Goddard/Adler/U.Chicago/Wesleyan)
Iron-60 forms inside massive stars and is released when those stars explode. Researchers already knew that traces of this isotope had reached Earth after nearby supernovae millions of years ago. But more recently, iron-60 has also been discovered in much younger Antarctic snow and deep-sea sediments, creating a mystery because no nearby stellar explosions have been observed recently.
This led researchers to suspect that the local interstellar cloud itself could store the material. According to the team, the solar system entered the clouds tens of thousands of years ago and is currently near its limits. They estimate that it will leave the cloud again in a few thousand years. If the cloud contains lingering supernova material, Earth would continue to collect small amounts of iron-60 while passing through it.
Antarctic ice appears to support this idea. Older samples contained less iron-60 than newer ones, a trend difficult to explain by the simple disappearance of remnants of supernovae that occurred millions of years ago. Instead, the results indicate that the isotope is unevenly distributed within the cloud itself.
The researchers also found that iron-60 levels appear to change surprisingly quickly, at least by cosmic standards, perhaps because different parts of the cloud contain different concentrations of this material.
Researchers melted more than 600 pounds of Antarctic ice to find iron-60
To find the isotope, the team transported about 300 kilograms (about 661 pounds) of Antarctic ice from Bremerhaven, Germany, to Dresden for chemical processing. The ice came from the EPICA ice drilling project, which stores some of the world’s oldest Antarctic climate records. After melting and filtering the samples, only a few hundred milligrams of dust remained. Somewhere inside were traces of iron 60.
The team then used particle accelerators and magnetic filters to isolate the isotope from about 10 trillion ordinary atoms. In the end, they only had a handful of iron-60 atoms left.
“It’s like looking for a needle in 50,000 football stadiums filled to the roof with hay. The machine finds the needle in an hour,” explains co-author Annabel Rolofs in the press release.
They also checked the samples using two other radioactive isotopes, beryllium-10 and aluminum-26, to ensure that no iron-60 had been accidentally lost during processing.
Antarctica may preserve a timeline of ancient stellar explosions
The team now hopes to analyze even older Antarctic ice, formed before the solar system entered the local interstellar cloud. These samples could help compare conditions before and after Earth began moving in the region.
For now, Antarctica appears to preserve something of a timeline of the solar system’s journey through interstellar space, recording the traces of dead stars that still drift through our corner of the galaxy today.
Learn more: Samples from asteroid Bennu contain mysterious space gums, sugars and a ton of stardust
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