Stardust in the Antarctic snow: Iron-60 discovery in the Antarctic provides information on the environment of solar system

Posted: November 15, 2019 by oldbrew in Analysis, research, solar system dynamics
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A 2016 article in Astronomy Now reported:
“Scientists found radioactive iron-60 in sediment and crust samples taken from the Pacific, Atlantic and Indian Oceans.

The iron-60 was concentrated in a period between 3.2 and 1.7 million years ago, which is relatively recent in astronomical terms, said research leader Dr. Anton Wallner from The Australian National University (ANU).

“We were very surprised that there was debris clearly spread across 1.5 million years,” said Dr. Wallner, a nuclear physicist in the ANU Research School of Physics and Engineering. “It suggests there were a series of supernovae, one after another.

“It’s an interesting coincidence that they correspond with when the Earth cooled and moved from the Pliocene into the Pleistocene period.” [bold added]

In August this year a new find was reported…
– – –
The rare isotope iron-60 is created in massive stellar explosions, says ScienceDaily. Only a very small amount of this isotope reaches the earth from distant stars.

Now, a research team has discovered iron-60 in Antarctic snow for the first time. The scientists suggest that the iron isotope comes from the interstellar neighborhood.

The quantity of cosmic dust that trickles down to Earth each year ranges between several thousand and ten thousand tons. Most of the tiny particles come from asteroids or comets within our solar system.

However, a small percentage comes from distant stars. There are no natural terrestrial sources for the iron-60 isotope contained therein; it originates exclusively as a result of supernova explosions or through the reactions of cosmic radiation with cosmic dust.

Antarctic Snow Travels around the World

The first evidence of the occurrence of iron-60 on Earth was discovered in deep-sea deposits by a TUM research team 20 years ago. Among the scientists on the team was Dr. Gunther Korschinek, who hypothesized that traces of stellar explosions could also be found in the pure, untouched Antarctic snow.

In order to verify this assumption, Dr. Sepp Kipfstuhl from the Alfred Wegener Institute collected 500 kg of snow at the Kohnen Station, a container settlement in the Antarctic, and had it transported to Munich for analysis.

There, a TUM team melted the snow and separated the meltwater from the solid components, which were processed at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) using various chemical methods, so that the iron needed for the subsequent analysis was present in the milligram range, and the samples could be returned to Munich.

Korschinek and Dominik Koll from the research area Nuclear, Particle and Astrophysics at TUM found five iron-60 atoms in the samples using the accelerator laboratory in Garching near Munich. “Our analyses allowed us to rule out cosmic radiation, nuclear weapons tests or reactor accidents as sources of the iron-60,” states Koll. “As there are no natural sources for this radioactive isotope on Earth, we knew that the iron-60 must have come from a supernova.”

Stardust Comes from the Interstellar Neighborhood

The research team was able to make a relatively precise determination as to when the iron-60 has been deposited on Earth: The snow layer that was analyzed was not older than 20 years.

Moreover, the iron isotope that was discovered did not seem to come from particularly distant stellar explosions, as the iron-60 dust would have dissipated too much throughout the universe if this had been the case.

Based on the half-life of iron-60, any atoms originating from the formation of Earth would have completely decayed by now. Koll therefore assumes that the iron-60 in the Antarctic snow originates from the interstellar neighborhood, for example from an accumulation of gas clouds in which our solar system is currently located.

“Our solar system entered one of these clouds approximately 40,000 years ago,” says Korschinek, “and will exit it in a few thousand years. If the gas cloud hypothesis is correct, then material from ice cores older than 40,000 years would not contain interstellar iron-60,” adds Koll.

“This would enable us to verify the transition of the solar system into the gas cloud — that would be a groundbreaking discovery for researchers working on the environment of the solar system.”

Source here.

  1. oldbrew says:

    The 2016 Astronomy Now article says the researchers ‘also found evidence of iron-60 from an older supernova around eight million years ago, coinciding with global faunal changes in the late Miocene.’
    – – –
    Supernovae showered Earth with radioactive iron

  2. oldbrew says:

    Supernovae in the neighbourhood
    Adrian L. Melott
    Nature volume 532, pages 40–41 (07 April 2016)

    The recorded supernovae occurred beyond the kill distance, and no major global mass extinctions coincide with them. However, during the suggested interval there was a general decline in temperature that culminated in the extensive series of glaciations in the Pleistocene epoch (from about 2.6 million to 12,000 years ago), although we do not know if there is a link between supernova activity and colder temperature. This climatic variation may be one of the conditions that led to human evolution. Ionization of the atmosphere by supernovae may also lead to an increase in lightning and possibly other climatic effects. [bold added]
    – – –
    11 OCTOBER 2017
    Confirmed: cosmic rays blast from supernovae

    Ending an astronomical mystery, scientists have confirmed that cosmic rays – high energy subatomic particles – are produced within at least one supernova.

    The rays, which consist primarily of protons and atomic nuclei, continuously bombard the Earth’s atmosphere. It’s been known for decades that they originate from outside the solar system, even perhaps outside the galaxy, but how and where they are created has until now remained obscure.
    – – –
    Microscopic ‘clocks’ time distance to source of galactic cosmic rays
    Supernova exploded in our ‘galactic neighborhood’ within the last few million years

    By Diana Lutz April 21, 2016

    The distance between the galactic cosmic rays’ point of origin and Earth is limited by the survival of a very rare type of cosmic ray that acts like a tiny clock. The cosmic ray is a radioactive isotope of iron, 60Fe, which has a half life of 2.6 million years. In that time, half of these iron nuclei decay into other elements.

    In the 17 years CRIS has been in space, it detected about 300,000 galactic cosmic-ray nuclei of ordinary iron, but just 15 of the radioactive 60Fe .

    “Our detection of radioactive cosmic-ray iron nuclei is a smoking gun indicating that there has been a supernova in the last few million years in our neighborhood of the galaxy,” said Robert Binns, research professor of physics in Arts & Sciences at Washington University in St. Louis, and lead author on the paper published online in Science April 21.

  3. Chaswarnertoo says:

    Iron fertilised ocean to reduce CO2? Anyone know?