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About 430,000 years ago, a glowing ball of hot gas rose out of the sky and crashed in Antarctica – and now scientists have found tiny debris formed by that impact.
The team recovered the mineral particles from Walnumfjellet in the Sør Rondane mountains of Queen Maud Land, Antarctic, which is located in the south of Africa in the east of the continent. Antarctica offers the ideal environment to research meteorite remains, due to its dry, frigid climate and minimal human presence, said first author Matthias van Ginneken, a geoscientist specializing in the study of micrometeorites, or extremely tiny meteorites the size of dust particles, has told Live Science.
“This was my first Antarctic expedition … and we found this very ideal sampling area on top of a mountain Sør Rondane,” said Van Ginneken, who is now conducting research at the University of Kent in United Kingdom, but during the study, held positions with the Free University of Brussels, the Vrije Universiteit Brussel and the Royal Belgian Institute of Natural Sciences. After collecting the sediment from the summit, Van Ginneken scanned the samples with an electron microscope.
Related: 50 amazing facts about Antarctica
“To my surprise, I found these very strange particles that didn’t look like Earth particles … but they didn’t look like micrometeorites either,” he said. Unlike micrometeorites, which look like fine dust, about half of the samples looked like several small stones fused together. Some had tiny patches of material on their surface, while others had distinct, almost snowflake-shaped markings, he said.
The chemical makeup of the particles suggests that they formed hundreds of thousands of years ago in an aerial explosion in the lower atmosphere, which occurs when a meteorite vaporizes before hitting the ground, according to the new study, published online March 31 in the journal. Scientific progress.
“If more of these unique touchdowns can be identified and even older particles are investigated, perhaps we can use them to understand the characteristics of the earlier ones. EarthSaid Maitrayee Bose, an isotope cosmochemist at Arizona State University (ASU) in Tempe, who was not involved in the study, told Live Science in an email.
Understanding the nature of these impacts could also help us prepare if such a meteor were to zoom in towards Earth again, but this time aimed at a bustling city instead of the Antarctic wilderness, Van Ginneken said.
Rebuild the impact
Upon seeing the unusual particles for the first time, “I said,” Bingo! It’s fantastic, fantastic stuff, ”said Van Ginneken. But the discovery was only the beginning of the story – to find out how these particles came to be, the team performed extensive chemical analyzes, searched the literature for reports of similar particles, and created numerical models. to visualize the original asteroid that created them.
“The document does a detailed analysis at every step … and does a great job convincing me that such an event may have occurred in Earth’s recent past,” Bose told Live Science.
The particles themselves were approximately 0.004 to 0.01 inches in diameter (100 to 300 micrometers) and mainly contained the minerals olivine and the iron spinel, which formed the snowflake-like patterns on some of the particles. These minerals were fused together by a small amount of glass. This composition closely matched a class of meteorites known as CI chondrites, confirming that the particles contained material from an asteroid, Van Ginneken said.
The large amount of nickel in the particles also pointed to an extraterrestrial origin, as nickel is not very abundant in the Earth’s crust, he added.
Related: Fallen stars: a gallery of famous meteorites
Knowing that these particles contain material from space, the authors then wanted to know where and how they formed once their parent meteoroid entered Earth’s atmosphere. the oxygen Isotopes in the particles – that is, forms of oxygen with different numbers of neutrons – revealed the amount of oxygen present during particle formation, Van Ginneken said.
Compared to the typical chondrite material, the samples were very rich in oxygen overall, suggesting that they formed in the atmosphere, but relatively close to the ground. That said, the particles contained very few heavy oxygen isotopes and specifically lacked an isotope called oxygen-18, the team found. This mimics the chemical composition of Antarctic ice, which contains little oxygen-18; Based on this, the team concluded that the particles interacted and mixed with the ice during their formation.
Then, to estimate when these particles formed, the team went looking for reports of similar meteor hits. It turned out that similar particles had been captured in ice cores from other parts of Antarctica, including two peaks known as EPICA Dome C and Dome Fuji. Studies suggest these meteorites fell to Earth 430,000 and 480,000 years ago, respectively, and comparing the new particles to these others, the authors estimated that the Walnumfjellet particles were formed 430,000 years ago.
“The mineralogical and textural evidence used in the article shows similarities between particles from different regions of Antarctica,” but despite these overlaps, the absolute age of the Walnumfjellet particles remains unknown, Bose said. Future scans will be needed to determine their precise age, more conclusively, she said.
Considering the size, shape and density of the particles, the team was also able to produce a “very rough calculation” as to the size of their parent asteroid, Van Ginneken said. The fused appearance of the particles suggests that the hot gas cloud they formed in was very large and very dense, which allowed the minerals to collide and blend into each other on their way to Earth. This suggests that the original asteroid was probably between 328 feet and 492 feet (100 and 150 meters) in diameter.
Based on their digital models, “it turns out that such an asteroid won’t reach the ground … basically it would be vaporized in a cloud of superheated meteor gas,” Van Ginneken said. The gas cloud would then continue to descend towards the ground at a speed similar to that of the original asteroid – “we are talking about kilometers per second,” he said.
“This very dense glowing plume that would reach the surface is extremely destructive. It could destroy a large city in seconds and cause serious damage for hundreds of kilometers, ”Van Ginneken said.
Aerial explosions occur much more frequently than impacts from asteroids that create large craters in the crust, he added. For example, an aerial explosion took place in Chelyabinsk, Russia, in 2013, and scientists also suspect that the massive explosion that leveled forests near Tunguska, Russia in 1908 was an aerial explosion, the authors wrote. authors in the Science Advances report.
Tunguska-type events are estimated to occur “once every 100 to 10,000 years, which is orders of magnitude more frequent than large crater-forming impacts,” the authors wrote. Studying the new Walnumfjellet particles could help scientists better understand how often these impacts occur and how much they damage the earth below, Van Ginneken said.
The study suggests “that we should be more worried about the smaller asteroids, between a few tens of meters and 200 meters [32-656 feet in diameter], than much bigger asteroids resulting in impact craters, “because smaller asteroids hit our planet more often, he said. If such asteroid starts rushing towards a small country, massive evacuation would probably be needed to spare people from the plume of fire, he said.
Originally posted on Live Science.
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