Scientists discover stardust in Antarctic snow

Stardust in the Antarctic snow
The Kohnen Station is a container settlement in the Antarctic, from whose vicinity the snow samples in which iron-60 was found originate. Credit: Martin Leonhardt/Alfred-Wegener-Institut (AWI)

A team of scientists hauled 500 kilograms of fresh snow back from Antarctica, melted it, and sifted through the particles that remained. Their analysis yielded a surprise: The snow held significant amounts of a form of iron that isn't naturally produced on Earth.

Other scientists had previously spotted the same rare isotope of iron in deep-ocean crusts. Called iron-60, it has four more neutrons than Earth's most common form of the element. But the iron-60 in the crust likely settled on the Earth's surface millions of years ago, as opposed to what was found in fresh snow in Antarctica that had accumulated over the past two decades.

"This is the first evidence that someone saw something that recent," said Dominik Koll, a physicist at Australian National University in Canberra and lead author of the study. The team published their findings this week in the journal Physical Review Letters.

Outer space objects ranging from dust to meteors regularly fall to Earth, but they are generally made of the same materials as our planet, since everything in the solar system, including the sun itself, assembled from the same building blocks billions of years ago. Because iron-60 is not among those common materials, it must have arrived from somewhere beyond the solar system.

"An [interstellar] meteor is a very rare event. However, the smaller the object size is, the more abundant it is," said Harvard astronomer Avi Loeb. Dust particles should rain down onto the Earth's surface more frequently, but picking them out from the myriad other particles around is a daunting task.

But at the South Pole, researchers need to account for possible Earthly sources of the isotopes, such as from nuclear power plants and nuclear weapons tests. Koll and his colleagues estimated how much iron-60 could be produced by nuclear reactors, tests, and accidents like the 2011 disaster in Fukushima, and they calculated only a minuscule amount. By studying additional isotopes like manganese-53, they also ruled out any significant contributions from cosmic rays, which generate iron-60 when they interact with dust and meteorites.

Stardust in the Antarctic snow
The Kohnen Station is a container settlement in the Antarctic, from whose vicinity the snow samples in which iron-60 was found originate. Credit: S. Kipfstuhl/AWI

What was left was hundreds of times more of the iron isotope than they expected. "That's really overwhelming," Koll said.

Bernhard Peucker-Ehrenbrink, a geochemist at Woods Hole Oceanographic Institution in Massachusetts, agreed that Koll's team clearly found a significant amount of interstellar iron. "Making these measurements is very difficult. You're essentially counting individual atoms," while weighing the contributions from background radiation. "Extracting that from half a ton of ice is not a trivial undertaking," he said.

Koll and his colleagues focused on iron-60 because it's rare, but not too rare, and it has a long lifetime, with a half-life of 2.6 million years. Many other isotopes that could have arrived from interstellar falling rocks are so unstable, with such short half-lives, that there's no way scientists could find them before they decayed away and disappeared.

Stars fling out a variety of tiny particles during their lifetimes, in addition to all the light and heat. But when the stars are younger, they're generally throwing out lighter metals, like carbon and oxygen. (Astronomers tend to refer to everything bigger than helium as a "metal.") Aging, massive stars and a certain type of supernova explosions, having spent many millennia fusing big nuclei into even bigger ones, can spew out particles of heavier metals, including iron-60 and its stable cousin, iron-56. Iron is usually the last element a star could produce while still generating energy, and after its last throes of life, it explodes. Only stars tens of times more massive than our sun could build iron isotopes, however, which means that the iron-60 found in Antarctica originated from outside the solar system.

"It must have been a supernova, not so near as to kill us but not too far to be diluted in space," Koll said.

That implies that our planet probably picked up the stray particles while traveling through the Local Interstellar Cloud, also known as the Local Fluff. This 30 light-year-spanning region, which the is currently passing through and just about to exit, likely formed from exploding blowing out the hot gases in their outer layers into space.

There are no supernovas going off now in our star's neighborhood, however, making it tough to pin down exactly where the isotope-enriched dust came from. Koll hopes that more data, like ice cores that reach deeper and older dust, could add more to the story. Such research would probe further into the past and could reveal more precisely when this alien dust started peppering our planet.

Explore further

Interstellar iron isn't missing, it's just hiding in plain sight

More information: Dominik Koll et al, Interstellar Fe60 in Antarctica, Physical Review Letters (2019). DOI: 10.1103/PhysRevLett.123.072701
Journal information: Physical Review Letters

This story is republished courtesy of Inside Science. Read the original story here. Used with permission. Inside Science is an editorially independent news service of the American Institute of Physics.

Citation: Scientists discover stardust in Antarctic snow (2019, August 20) retrieved 19 September 2019 from
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Aug 20, 2019
First off the solar system is not billions of years old any moron can prove by science earth is around 7-10 thousand years old the moon maybe a little older and man did not evolve from apes or any other creatures we were created in the likeness of our creator god
This garbage about evolution and million and billion years was started by Charles Darwin as a theory the followers of Darwinism have pushed to try to convince the world that it is factual
All scientist prior to Darwin believed in creationist theology. Sir issac newton back to the first scientist this crap of dinosaurs roaming the earth billion of years is a big lie dinosaurs are recorded to have roamed the earth in the book of genesis

Aug 20, 2019
Just as science also proven if the earth and moon were million of years the layers of dirt would so much that all know rivers and tributaries would be clogged by dirt deposits that no rivers could flow and if the moon were millions of years. When man would have set foot on the surface they would have sunk because the moon dust would measure a few feet deep not inches

Aug 20, 2019
dinosaurs are recorded to have roamed the earth in the book of genesis

Is it painful to be that stupid? If not, it should be.

Aug 20, 2019
There are no multivariate isotope statistics compared systematically in this study. Avi Loeb strikes again with his unbelievably self-directed arguments toward his untenable and disproven alien light-sail alibis. His highly error-affected inference embraced 10% error (actually >60%) for New Guinea putative interloper, observed during a magnetospheric proton storm - conditions that cause the same US government monitors to produce false positives for nuclear detonations; Many terrestrial sources, including nuclear reactors, volcanic events that sample enriched magmatic reservoirs, and industrial facilities - even thunderstorms - expected to produce a similar signature. A supernova is the most likely source, not 'Oumuamua or the overblown interstellar stream that he proposes. 'Oumuamua was also observed during a 12-year solar flux peak, which no study considered (all assume avg. foreground values). Its light curve is amplitude and phase synchronized w/solar flux (error, not boosts).

Aug 21, 2019
Iron-60 the most reliable astrophysical chronometer

500 kilograms of fresh snow from Antarctica
Melted and sifted
The particles that remained
Yielded a surprise
The snow contained a form of iron not produced on Earth.

Other scientists spotted this isotope of iron in deep-ocean crusts
Called iron-60
Has four more neutrons than Earthly iron
For this iron-60 was found in fresh snow in Antarctica ten years old

Nailing the half-life of iron-60 by PW
The most accurate measurement yet of the half-life of iron-60
Has been made by an international team of physicists
While previous measurements of the half-life had differed by a factor of two
The team says that it has accounted for most sources of error that plagued earlier experiments
The radioactive isotope
Whose half-life is measured at 2.60 million years
Can now be used to date astrophysical events on that timescale
Making it a reliable astrophysical chronometer

Aug 21, 2019
coefficients near 1.6^2 are common errors. Decay curves require understanding of initial values, and subsequent modification during residence on Earth. Iron-60 is assumed here to be uniquely non-terrestrial, but nuclear processes and modified volcanic redeposition of cosmic iron-60 can be sampled by convective processes. "Most sources of error" do not anticipate recent anthropogenic production, as stated in the article. The problem isn't the finding, it's that Avi Loeb and others will co-opt a discovery to serve past blatherings without considering that there are as stated several possible routes toward the accumulation of iron-60 (cf. 14C was believed to only have a cosmic ray source mechanism, but now we know that lightning contributes the terrestrial abundances. https://agupubs.o...075131). The point is to watch your foreground. We are experiencing a kind of revolution in hubris, geophysical/heliophysical ignorance is becoming clearer.

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