430,000 years ago, a huge fireball hit Antarctica

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About 430,000 years ago, a huge glowing ball of hot gas crashed into Antarctica. A few months ago, scientists found tiny debris formed just before impact. Details of the study are published in the journal Scientific progress.

A team led by geoscientist Matthias van Ginneken from the University of Kent (UK) recently sampled sediment atop one of the Sør Rondane mountains in the Queen Maud Land region. To locate you, we are north of the white continent. Electron microscopic analyzes then underlined the presence of mineral particles.

“To my surprise, I found these very strange particles that didn’t look like Earth particles… but they didn’t look like micrometeorites either.”, writes the researcher.

“Unlike micrometeorites, which look like fine dust, about half of the samples looked like several small stones fused together,” he continues. “Some had tiny specks of material on their surface, while others had distinct, almost snowflake-shaped markings.”.

An extraterrestrial origin

Chemical analyzes revealed that these particles (100 to 300 micrometers in diameter) contained mainly olivine and spinel (rich in iron) fused by a small amount of glass. According to the authors, this composition closely matched that of a class of meteorites known as CI chondrites, confirming that these particles contained material from an asteroid.

The large amount of nickel contained in the particles also confirmed an extraterrestrial origin. As a reminder, this element is not very abundant in the earth’s crust.

For the researchers, the chemical makeup of the particles suggests that they formed several hundred thousand years ago during a air explosion in the lower atmosphere. In fact, they would probably be the work of a large meteorite vaporizing before touching the ground. But at what level were they formed?

To find out, the researchers focused on the oxygen isotopes of these particles (oxygen elms with different numbers of neutrons) in order to assess the amount of oxygen present during their formation. Compared to typical chondrite material, samples were here very rich in oxygen, which suggests that they are formed very close to the ground.

Some of the impact particles collected in the mountains of Sør Rondane, Antarctica. Credit: Scott Peterson

A violent impact 430,000 years ago

To date this event, the team turned to other reports of similar meteor hits.

It turned out that similar particles have already been captured in ice cores taken from two other Antarctic peaks (EPICA Dome C and Dome Fuji). According to these studies, these meteorites fell to Earth respectively 430,000 and 480,000 years. By comparing these new particles with those already dated, the authors estimate that they formed about 430,000 years ago.

Finally, given the size, shape and density of these alien remains, the team attempted to estimate the size of their parent asteroid: between 100 and 150 meters in diameter.

On the basis of numerical simulations, it turns out that such an asteroid could not reach the ground. “Instead, it would be vaporized in a cloud of superheated meteor gas”, note Dr Van Ginneken. “The gas cloud would then continue to fall towards the ground at a speed similar to that of the original asteroid. We are talking about kilometers per second ”.

Here the gas ball is crushed in Antarctica, but note that such a dense and glowing plume would be extremely destructive if impacted in a populated area. Thus the study suggests “That we should be more worried about these smaller asteroids – measuring a few tens of meters to 200 meters in diameter – than much larger asteroids causing impact crater events”.

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