A massive impact crater has been detected beneath the Greenland icecap

An unusually large asteroid crater, measuring 19 km wide, has been discovered beneath a layer of continental ice in Greenland. Of an approximate size, Paris is one of the 25 largest craters of asteroids on the planet.

An iron-rich asteroid measuring nearly a kilometer wide hit Greenland's ice-covered surface between 3 million and 12,000 years ago, according to a new study published today in Science Advances.

The impact would have projected horrible amounts of water vapor and debris into the atmosphere, while sending torrents of meltwater into the North Atlantic – events likely to trigger global cooling (sometimes called winter phenomenon nuclear or volcanic). Over time, however, the gaping hole was masked by a 1,000-meter (3,200-foot) layer of ice, where it remained hidden for thousands of years.

Remarkably, the crater was discovered by chance – and it's now the first big crater to be discovered under a layer of continental ice.

"In 2015, I was looking at a new map of bedrock beneath the Greenland Ice Cap and I discovered a large circular element beneath the Hiawatha Glacier in northwestern Greenland," said Nicolaj K. Larsen, co-author of the study and geoscientist in Aarhus. University, told Gizmodo. "In other words, it's a coincidence that the crater was discovered."

Larsen, along with his colleague Kurt Kjaer of the Natural History Museum of Denmark, immediately acknowledged that they had stumbled upon something special, but it soon became clear that depression would be difficult to confirm as a remnant of an old asteroid shot.

The first step was to analyze aerial surveys conducted in Greenland from 1997 to 2014 by researchers at the University of Kansas. But the resolution of the data from these surveys "was not enough," according to Larsen. A team was sent to Greenland to collect high quality, higher resolution radar data from the Hiawatha Glacier and the underlying bedrock. This was accomplished in 2016 with the aid of a broadband radar penetrating the ground (or in this case, an ice-penetrating radar) developed at the University of Kansas. .

That said, the signs of the impact crater were also visible to the naked eye.

"You can see the rounded structure at the edge of the ice cap, especially when you fly high enough," said John Paden, co-author of the study and engineer at the University of Kansas. "The crater is usually not visible through the window of the plane. It's funny that until now, no one has said to himself: "Hey, what is this particularity in a semicircle?" From the plane, it's hard to see if we already know it. By using satellite images taken at a low sun angle that accentuates the hills and valleys of the ice cap terrain, you can really see the circle of all the crater in these images. "

The scientists then went to the edge of the glacier to collect river samples. Some of the minerals analyzed exhibited the hallmarks of a catastrophic impact, such as shocked quartz grains and other impact-related grains, such as glass.

Some preglacial channels were seen under the ice cap at the crater site, suggesting that the Greenland Ice Cap was already in place when the asteroid struck the surface. The exact moment of the asteroid strike, however, is rather vague, the researchers claiming that it happened between 3 million and 12,000 years ago. But preliminary evidence suggests that this has happened relatively recently. The crater seems to be well preserved – a surprising observation given that ice is a powerful erosive force. The crater is probably quite young from a geological point of view.

"It is true that the crater is not well dated, but there is good evidence that it is geologically young, that is to say it was formed in the last 2 to 3 million years and most likely as young as the last ice age. [which ended around 12,000 years ago]Larsen explained to Gizmodo. "We are currently trying to come up with ideas on how to date the impact. One of the ideas is to drill through the ice and get rock samples that can be used for digital dating. "

In addition, the incident was serious enough that it was possible to detect the evidence of impact elsewhere on the planet. The impact probably triggered a global cooling phenomenon by releasing large amounts of debris, dust and water vapor into the atmosphere, blocking incoming solar radiation. At the same time, the melting of the Greenland ice would have reached the North Atlantic, which would weaken or stop the North Atlantic Current – the current that provides a relatively mild climate for Western and Northern Europe. Evidence of the impact should therefore exist in the stratigraphy of our planet, allowing a more precise dating of the impact. Archaeologists and anthropologists could also help in this regard, to determine if and when the ancient human populations were affected by an asteroid attack dating from this period.

The discovery of this crater in Greenland, hitherto unknown, is good news, both in terms of learning and for this one, and for the future scientific work that it will inspire for sure. Confirming the existence of this crater is only the first step – there is now a lot of related work to do.

[Science Advances]