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The rare iron isotope 60 is created during massive stellar explosions. Only a very small amount of this isotope reaches the Earth from distant stars. Today, a highly involved research team from the Technical University of Munich (TUM) has discovered iron 60 for the first time in the Antarctic snow. Scientists suggest that the iron isotope comes from the interstellar neighborhood.
The amount of cosmic dust that spreads on the Earth each year varies between several thousand and ten thousand tons. Most of the small particles come from asteroids or comets in our solar system. However, a small percentage comes from distant stars. There are no natural terrestrial sources for the iron isotope 60 contained in it; it comes exclusively from supernova explosions or reactions of cosmic radiation with cosmic dust.
Antarctic snow travels around the world
The first evidence of the presence of Iron 60 on Earth was discovered by a TUM research team in deep water deposits 20 years ago. Dr. Gunther Korschinek, one of the scientists in the team, hypothesized that traces of stellar explosions could also be found in pure and intact Antarctic snow. To test this hypothesis, Dr. Sepp Kipfstuhl, of the Alfred Wegener Institute, collected 500 kg of snow at the Kohnen station, a container colony located in Antarctica, and did it. transport to Munich for analysis. A TUM team melted the snow and separated the meltwater from the solid components, which were treated at Helmholtz-Zentrum Dresden-Rossendorf (HZDR) using various chemical methods, so that the iron needed to the subsequent analysis is present in the milligram. range, and the samples could be returned to Munich.
Korschinek and Dominik Koll from the Nuclear, Particle and Astrophysics research area of TUM discovered five iron 60 atoms in the samples using the Garching Accelerator Laboratory near Munich. "Our analyzes have allowed us to eliminate cosmic radiation, nuclear weapons tests or reactor accidents as sources of iron 60," says Koll. "Since there are no natural sources for this radioactive isotope on Earth, we knew that Iron 60 had to come from a supernova."
Stardust comes from the interstellar neighborhood
The research team was able to determine with relative accuracy the moment when iron 60 was deposited on Earth: the layer of snow analyzed was not more than 20 years old. In addition, the iron isotope discovered did not appear to come from particularly distant stellar explosions because iron dust 60 would have dissipated too much in the universe if that had been the case. On the basis of the half-life of iron 60, all atoms from the formation of the Earth would have completely decomposed. Koll therefore assumes that the iron 60 in the Antarctic snow comes from the interstellar neighborhood, for example from an accumulation of gas clouds in which our solar system is currently located.
"Our solar system went into one of these clouds about 40,000 years ago," says Korschinek, "and will leave it in a few thousand years." If the cloud hypothesis gas is correct, materials from ice cores over 40,000 years old will not contain interstellar iron-60, "adds Koll. "This would allow us to verify the transition from the solar system to the gas cloud – it would be a breakthrough for researchers working on the solar system environment.
D. Koll, G. Korschinek, T. Faestermann, J. M. Gómez-Guzmán, S. Kipfstuhl, S. Merchel, J. Welch M.: Interstellar 60Fe in Antarctica. In: Physical Review Letters 123, 072701. August 2019.
DOI: 10.1103 / PhysRevLett.123.072701 https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.123.072701
Astrobiology, astrochemistry
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