Aug. 21 (UPI) -- Australian scientists found stardust in freshly melted snow from Antarctica, discovering large amounts of a rare isotope not natively found on Earth.
The researchers ruled out the chance that iron-60 found in the snow was made by human action and, based on research published this month in the journal Physical Review Letters, it was delivered to Earth by some type of interstellar falling rock.
While Earth's most abundant element is iron, iron-60 has four more neutrons than the well-known element. Scientists say that iron-60 can be found in the Earth's crust, but the source can't be the same as the new finding because it was in snow that has accumulated in recent decades.
"Making these measurements is very difficult," Bernhard Peucker-Ehrenbrink, a geochemist at Woods Hole Oceanographic Institution, said in a press release. "You're essentially counting individual atoms."
Researchers melted about 1,100 pounds of snow from Antarctica, examining what was left behind.
They ruled out the creation of iron-60 from nuclear power plants and weapons tests, finding only a small amount could make it to the South Pole, and study other isotopes to determine if iron-60 was generated by cosmic rays after interacting with dust or meteorites.
Interstellar meteorites are rare, according to Avi Loeb, an astronomer at Harvard, but "the smaller the object size is, the more abundant it is."
With this in mind, there researchers say the source of iron-60 must be a supernova, "not so near as to kill us, but not too far to be diluted in space," said lead researcher Dominik Koll, a physicist at Australian National University.
Koll said that, in this case, the particles may have been picked up as Earth travels through the Local Interstellar Cloud, a 30-light-year wide region of space that our solar system is currently passing through.
More research is necessary to understand where and when the iron-60 got to Earth -- it has a half-life of 2.6 million years -- which Koll said will require more data and ice cores that go deeper into the planet, reaching older dust.
"This is the first evidence that someone saw something that recent," Koll said.