News of August 13, 2019
Stardust in the Antarctic
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. A small proportion, however, comes from remote stars. 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 at the Technical University of Munich (TUM), in collaboration with colleagues at two Helmholtz Centers, have now discovered iron-60 in the Antarctic for the first time. They have been able to draw spectacular conclusions from their findings.
Text: Thomas Bührke
It all started in 2015: Sepp Kipfstuhl from the Alfred Wegener Institute (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 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 seabed 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. A team at the TUM then melted the snow and separated the solid components from the melted snow using fine paper filters. A total of 13 filters were then sent to the Helmholtz-Zentrum Dresden-Rossendorf (HZDR), where Silke Merchel was to extract the solid components from the paper using every trick in the chemistry book. “I practiced in advance with empty filters, so that nothing would go wrong during the final work on the valuable sample,” the chemist recalls. “Apart from that, I checked which elements were already contained in the filters and the chemicals we used, as the measurements to be performed later on were so sensitive that you could find everything with them.” From the total of 13 filters containing the actual sample, a colleague from Dresden sorted out obvious impurities under the microscope and they were then burned at 650 degrees Celsius. “We processed the ashes for about three weeks using traditional chemical methods, until we had obtained the few milligrams of iron needed for the subsequent analysis,” the researcher from Dresden explains. “These minute samples of iron were taken to Munich in person by a colleague from the HZDR.”
Find out what discovery the researchers made there on helmholtz.de.
D. Koll, G. Korschinek, T. Faestermann, J. M. Gómez-Guzmán, S. Kipfstuhl, S. Merchel, J.M. Welch: Interstellar 60Fe in Antarctica, in Physical Review Letters, 2019 (DOI: 10.1103/PhysRevLett.123.072701)
Department of Nuclear Physics at Australian National University
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Dr. Gunther Korschinek
Department of Physics at Technical University Munich
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Dr. Silke Merchel
Institute of Ion Beam Physics and Materials Research at HZDR