Scientists discover star dust in Antarctic snow

A team of scientists transported 500 kg of fresh snow from Antarctica, melted it and filtered the remaining particles. Their analysis gave a surprise: the snow contained significant amounts of naturally occurring iron not produced on Earth.

Other scientists had previously spotted the same rare isotope of iron in deep ocean crusts. Called iron 60, it contains four more neutrons than the most common form of the Earth. But the iron 60 present in the crust probably was deposited on the surface of the Earth millions of years ago, unlike what was found in the fresh Antarctic snow that s & rsquo; Was accumulated over the last two decades.

"This is the first evidence that someone has seen something so recent," said Dominik Koll, a physicist at the Australian National University of Canberra and senior author of the University of California. ;study. The team published its findings this week in the newspaper Letters of physical examination.

Space objects, ranging from dust to meteors, regularly fall on the Earth, but they are usually made with the same materials as our planet, because everything in the solar system, including the sun, is assembled at from the same building blocks there are billions of years. Since Iron 60 is not one of these common materials, it must come from somewhere in the solar system.

"A [interstellar] Meteor is a very rare event. However, the smaller the size of the object, the more abundant it is, "said Harvard astronomer Avi Loeb.Dust particles should rain more frequently on the surface of the Earth, but extract them from the Earth. myriad other particles is a daunting task.

But at the South Pole, researchers must take into account any terrestrial sources of isotopes, such as nuclear power plants and nuclear weapons tests. Koll and his colleagues estimated the amount of iron 60 that can be produced by nuclear reactors, tests and accidents such as the Fukushima disaster in 2011, and they calculated a tiny amount. By studying other isotopes such as 53-manganese, they also excluded any significant contribution of cosmic rays, which generate iron 60 when they interact with dust and meteorites.

What remained was hundreds of times more iron isotope than expected. "It's really overwhelming," Koll said.

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

Koll and his colleagues focused on Iron 60 because it is rare, but not too much, and its shelf life is long, with a half-life of 2.6 million years. Many other isotopes that could have come from interstellar rock falls are so unstable, with such a short half-life, that it is impossible for scientists to find them before they decompose and disappear.

Stars throw a variety of tiny particles throughout their life, in addition to all the light and heat. But when the stars are younger, they usually reject lighter metals, such as carbon and oxygen. (Astronomers tend to call "metal" anything that is bigger than helium.) Aging, massive stars and some type of supernova explosions, having spent many millennia to melt large cores in even larger cores, can spread heavier metal particles, especially iron 60 and its stable cousin, iron 56. Iron is usually the last element that a star can produce while producing of energy and, after her last pangs, she explodes. However, only stars tens of times more massive than our sun could build iron isotopes, which means that the iron 60 that is found in Antarctica comes from outside the solar system.

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

This implies that our planet has probably captured parasitic particles as it passes through the local interstellar cloud, also known as local fluff. This region of 30 light-years, which the solar system is crossing and about to leave, is probably formed of massive exploding stars projecting hot gases from their outer layers into space.

No supernova now fires in the vicinity of our star. It is therefore difficult to determine exactly where the isotope-enriched dust is coming from. Koll hopes that more data, such as ice cores that reach the deepest and oldest dusts, could add more to the story. Such research would deepen the past and could reveal more precisely when this foreign dust began to pepper our planet.

This story is reissued with permission from Inside Science. Read the original story here. Used with permission. Inside Science is an independent editorial news service of the American Institute of Physics.