A huge impact crater was discovered under a half-mile Greenland ice sheet.
The enormous shape of the cup seems to be the result of a mile-long iron meteorite striking the island at 12 miles per second, just like 12,000 years ago.
The impact of a 10-ton cosmic rock would produce 47 times more energy than the Little Boy atomic bomb dropped on Hiroshima in 1945. It would melt a lot of ice, send fresh water to the oceans and blast the rocky garbage into the air. atmosphere.
Being 19.3 miles wide, the crater ranks among the 25 largest known on Earth and is the first found under the ice cover.
"You have to go back 40 million years to find a crater of the same size, so it's a rare, rare phenomenon in Earth's history," said Kurt Kjær of the Natural History Museum in Copenhagen.
Researchers first suspected the crater in 2015, when they noticed a huge depression in NASA's radar images under the Hiawatha glacier in Northwest Greenland. Kjær, who goes through a 20-ton meteorite to get to his office every day, wondered if such a cosmic stone could be the culprit. "It's all from there," said Joseph MacGregor, senior team scientist at the Goddard Spaceflight Center in Maryland.
It so happened that researchers from the Institute Alfred Wegener in Germany was about to test a new, powerful, ice radar system that was operated from the air. In May 2016, the scientists flew over the Hiawatha glacier and used the radar to reproduce the hidden rock in unsurpassed details.
Images revealed all the features of the impact crater. "It has become clear that it is a circular element with a ring around it and an elevated central region," said Kjær. The bowl itself was over 300 meters deep, according to a report in the journal Science Advances.
To find a solid proof of impact, the scientists recommended the glacier and collected sediments that rinsed from the crater into the nearby flood plains. Of the collected grains, scientists found particles of shocked quartz and other materials that are usually produced by extraterrestial violence. Geochemical studies of grains suggest that the meteorite was made of iron.
So far, you could not bet on the crater, but its condition suggests that it arose after the ice began to encompass Greenland about 3 million years ago. But the crater could have arisen much recently. Radar images show that while the surface layers of the glacier just above the crater look normal, deeper layers that are older than 12,000 years are seriously deformed and strewn with stones, with a few lumps as heavy as trucks.
"When this happened, a $ 64,000 question," said MacGregor. To get the final answer, the scientists will have to drill half a mile of ice and collect the crater material for dating or wait until the rocks from the impact pool are discharged to the surface when the glacier flows into the sea. Either way, scientists are waiting for their hands.
"We live on a planet where everything can be viewed and you think you know everything," said Kjær. "But when you see such a great thing as the one hidden in view, you realize that the age of discovery is not over yet."