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“Asteroids have to be massive enough to pass through the atmosphere and reach the ground with enough speed to form an impact crater. Smaller objects, which are much more abundant, explode in the atmosphere and do not form a crater. “said Mark Boslough, a researcher at the University of New Mexico, who has studied meteor explosions but was not involved in this latest study.
Matthias van Ginneken, a research associate at the School of Physical Sciences at the University of Kent, collected the 17 dark black particles – all smaller than 1 millimeter and invisible to the naked eye – during an expedition in the Sør Rondane mountains, Queen Maud Land, in East Antarctica, where the Belgian station Princess Elisabeth Antarctica is based.
“I first noticed that some of them seemed to have been glued together, which should have happened when they were melted down. This would have meant that many of them interacted with each other when they were at a very high temperature. The only Sane way to explain this has had a huge impact, ”said van Ginneken, lead author of the study published Wednesday in the journal Science Advances.
‘Impact of touchdown’
He and a team of international scientists were able to piece together what happened when the ancient meteorite entered Earth’s atmosphere by analyzing the microscopic particles. Their chemistry and high nickel content suggest they originated in outer space.
The researchers compared them to similar particles found in two ice cores, which serve as a record of past geological conditions. The samples, dated to 430,000 years ago, were taken from other places in East Antarctica. Numerical modeling examining the distribution and density of the particles suggested that the meteorite was between 100 meters and 150 meters wide.
Although the meteorite did not create a crater, it would have wreaked havoc on the ground.
“It was a touchdown impact. Like an explosion in the atmosphere that creates this very hot cloud of gas that travels very quickly towards the ground,” said van Ginneken.
He said if a weather event like this occurs over a densely populated area, it will result in millions of casualties and severe damage over distances of up to hundreds of kilometers.
There are eyewitness accounts for two smaller but more recent aerial explosions – although in both cases no fireballs made contact with the Earth’s surface.
A powerful asteroid is believed to have struck the Podkamennaya Tunguska River region in an isolated Siberian forest in Russia in 1908 – although the idea was considered far-fetched at the time. The event leveled trees and destroyed forests over 1,200 square kilometers, nearly three-quarters the size of the US state of Rhode Island. The impact knocked people to the ground in a town 40 miles away.
Boslough, the University of New Mexico researcher who was not involved in this study but who studied the Chelyabinsk meteor explosion, said the article provided good evidence for the meteor explosion at over Antarctica 430,000 years ago.
“The details of what happened were inferred from the structure, shape, chemistry and minerology of the particles. We don’t know of any other process that could form them,” he said.
“Therefore, air burst events occur much more often than crater events. The geological evidence for an air blast is not as obvious as that of a solid impact, but this article is a strong argument. “
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