Ice research in Greenland has uncovered evidence suggesting the impact of a kilometer-long iron asteroid on this island, perhaps only 12,000 years ago.The crater was formed from a collision, 30 kilometers wide, it remained hidden for the time being under a layer of ice with a thickness of 800 meters.
It has been recently disclosed by an ultra-broadband radar system developed at the Center for Remote Detection of Ice Platforms (CReSIS), based at the University of Kansas (KU) in the United States. The crater's characteristics, the result of the impact under the Hiawatha glacier in the far north-west Greenland, is described in detail in an article published in Science Advances.
This has been identified on the basis of data collected in 1997-2014 by KU for the NASA program in the area of regional assessment of the Arctic climate and Operation IceBridge. They were supplemented with more data collected in May 2016. Using a coherent radar with a multi-channel probe. depth (MCoRDS), developed at KU.
"We've collected a huge amount of radar research data in the last two decades, and the glaciologists have gathered this information to map what Greenland is like ice," says co-author John Paden, associate professor of electrical engineering and science. Calculations at KU and researcher at CReSIS.
"Danish researchers looked at the map and saw this great depression, similar to the crater, below the ice cover and the observed satellite images, and Because the crater is on the edge of the ice cover, you can also see a round pattern there. Based on this discovery, in May 2016, a detailed radar survey was carried out using the most modern radar designed and built by KU for the Alfred Wegener Institute in Germany "- he adds.
Paden, who helped develop MCoRDS radar signal processing software, participated in low-level flights in the grid over the impact crater to specify its dimensions.
"You see a rounded structure on the edge of the ice cover, especially when you fly high enough," he says. Most of the time, the crater can not be seen through the window of the plane. Using satellite images taken at a low angle of the sun, which emphasize the hills and valleys in the area of the ice cover, you can really see the circle of the entire crater in these images. "
To confirm the discovery of satellites and radars, the research team carried out further soil studies of glaciofluvial deposits in a larger river that emptied the crater. The work showed the presence of "struck quartz and other impact-related grains", such as glass. The research team believes that these rocks and glassy grains are probably formed as a result of the impact fusion of grains in the parent parental rock.
Specify the date of receipt
The work still more accurately determines the moment of impact of the asteroid in Greenland. The authors say so there is evidence to suggest that Hiawath's impact crater was created during the Pleistocene, because this age is more consistent with the conclusions of the data currently available. However, even this wide range remains "uncertain" over time. To the southwest of the crater, the team discovered a region rich in potential shards ejected from impact, which can help to limit the range of dates.
"It would throw pollutants into the atmosphere that could affect the climate and the ability to melt a lot of ice, so that there could be a sudden flow of fresh water in the Nares Strait, between Canada and Greenland that would affect the entire ocean's flow in the region," he argues. Paden. Evidence suggests that the impact probably occurred after the Greenland ice sheet was created, but the research team is still working on the exact date. "
According to the planetary geologist David Tovar, the discovery of the Greenland crater shows that there are several regions of the planet that can still keep evidence of impact craters. "Many times these structures are not taken into account by geologists due to the lack of knowledge about their training processes and the type of material that the asteroid affects different types of rocks," says the expert. .
"Similarly – he continues – it is obvious that the work associated with obtaining remote sensing data (satellite images, aerial photographs, geophysics) is very helpful if we want to examine impact structures that are covered by a certain type of material, in this particular case ice."
Tovar points to this this work should be complemented by field visits, during which scientists with knowledge of planetary geology should collect evidence in hand samples, "That is, rock samples with typical structures produced by impacts that will later be analyzed in the laboratory, with the ultimate goal of combining key evidence at different scales: mega, macro and microscopic." A work that takes years and should not be done lightly. "