Supernovae
Stardust in the Antarctica
Iron-60 discovered in Antarctic snow samples
[16. August 2019]
The rare isotope iron-60 is produced by huge star explosions. Only a small proportion comes from remote stars. Researchers have now discovered iron-60 in the Antarctic for the first time. They have been able to draw spectacular conclusions from their findings.
Every year, several thousand to tens of thousands of tons of cosmic dust shower down on the Earth. Most of these tiny particles come from asteroids and comets in our solar system. The iron-60 isotope contained in these particles is particularly interesting. Natural sources of this isotope do not exist on Earth. On the other hand, exploding stars, so-called supernovae, emit large quantities of iron-60. Researchers have now discovered iron-60 in the Antarctic for the first time.
It all started in 2015: Sepp Kipfstuhl from the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI), was once again visiting the Kohnen Station, a container settlement located around 750 kilometers from the Neumayer III research station. Kipfstuhl was researching how trace substances are deposited in ice. A request sent by Gunther Korschinek from the Technical University of Munich (TUM)presented him with a welcome diversion. He was asked to collect 500 kilograms of snow and pack it in boxes. Twenty years ago, Korschinek and colleagues at TUM had already found evidence of iron-60 in deep sea deposits.
It was a sensational discovery, since it led the researchers to conclude that several supernovae must have exploded in the vicinity of the sun around two million years ago. They inferred this from the depth distribution in a manganese crust taken from the ground of the Pacific Ocean, in which they found iron-60 that had been deposited on the sea bed over the course of millions of years. On the strength of this, Korschinek wondered where he might possibly find further iron-60 deposits from stellar explosions in the past as the solar system is just passing through a denser interstellar environment. This was a difficult undertaking since the fine dust from the cosmos is usually lost in nature. He believed, however, that it might be possible to detect the dust in the pure snow of the Antarctic. “So we got our spades out and shoveled snow,” Kipfstuhl recalls. Afterwards the sample, still frozen, was sent off on its long journey.
The 25 boxes were flown by plane to the Antarctic coast; from there they were taken to Cape Town on a South African research vessel and finally transported to Munich via the AWI in Bremerhaven.
Scientists from various institutes then melted the snow and separated the solid components from the melted snow using fine paper filters. Even the filtered water was reused to evaporate it using a rotary evaporator. Finally, the extremely rare iron-60 could actually be detected.
But the fact that the iron-60 found originates from supernova explosions makes it all the more interesting for researchers. This isotope is unstable and decays; every 2.6 million years the quantity originally available is halved. If iron-60 had been present 4.6 billion years ago during the Earth’s formation, it would have completely decayed by now. If evidence of this isotope is found somewhere, it must have come from space relatively recently by astronomical standards. However, this iron-60 did not shower down on the Earth millions of years ago, as the snow collected was no more than 20 years old. It does not seem to have come from far-distant supernovae, because otherwise the iron-60 dust would have been too greatly depleted in the universe.
Contact
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Markus Brand
+49(4725)819-3131
Markus.Brand@awi.de
Wissenschaft
Dr. Sepp Kipfstuhl
+49(471)4831-1175
Sepp.Kipfstuhl@awi.de