An ice study in Greenland has revealed evidence indicating the impact of a kilometer-long iron asteroid on the island, perhaps 12,000 years ago.The crater created by the collision, 30 km wide, remains hidden until now under an 800 m thick ice layer.
It was recently exposed by an ultra-wide radar system developed at the Center for Remote Identification of Ice Platforms (CReSIS), based at the University of Kansas (KU) in the United States. The characteristics of the crater, the result of the impact under the Hiawatha glacier in the northwestern part of Greenland, are detailed in an article published in "The Progress of Science".
It was identified with data collected between 1997 and 2014 by the KU for the NASA program for Arctic Regional Climate Assessment and IceBridge Action, and was supplemented with additional data collected in May 2016 using coherent multichannel probe radar. Depth (MCoRDS), developed in KU.
"We have collected a large amount of radar survey data over the past two decades, and geologists have collected this information to produce maps of Greenland as below ice," says co-author John Padan, a professor of electrical and scientific engineering. Associate at CReSIS.
"Danish researchers looked at the map and saw this great depression, like a crater, under the ice sheet and watched satellite images, As the crater is on the edge of the ice sheet, you can also see a circular pattern there. Based on this discovery, in May 2016, a detailed radar study was conducted using a new and sophisticated radar designed and built by the KU for the Alfred Wagner Institute in Germany, "he adds.
Padan, who helped develop the MCORDS signal processing software, participated in low-altitude model flights over a crater that had the effect of detailing its dimensions.
"You can see the curved structure at the edge of the ice, especially when you fly high enough," he says. For the most part, the crater can not be seen through the window of the plane. Using satellite images taken at low angle of the sun, which emphasizes the hills and valleys in the area of ice ice, you can see the entire circle of the crater in these pictures. "
To confirm the satellite and radar findings, the research team conducted additional ground studies on the glaciofluvial residue of the larger river that cleaned the crater. The work showed the presence of "affected quartz and other impact-related grains," such as glass. The research team believes that these glassy vitreous rocks are likely to be produced from the fusion effect of metasedimentary parent grain grains.
Determining the date of impact
The work continues to determine more precisely the moment of influence of the asteroid in Greenland. The authors say that There is evidence suggesting that the Hiawatha impact crater was formed during the Pleistocene, Since this age is consistent with the assumptions of the existing data today. However, even this wide-ranging time remains "unsafe". Southwest Crater, the team found a potentially rich waste area ejected from the impact, which could help reduce the date range.
"It would throw debris into the atmosphere that would affect the climate and the potential to melt a lot of ice, so there could be a sudden flow of fresh water in the Nares Strait, between Canada and Greenland, which would affect ocean flow in this whole area," Padan says. The evidence suggests that the effect probably occurred after Greenland's ice sheet was created, but the research team is still working on the exact date. "
According to astrologer David Tubar, The discovery of the crater in Greenland shows that there are several areas of the Earth that can still preserve evidence of impact craters. "Many times, these structures are not taken into account by geologists due to lack of knowledge about their training process and the type of material that the asteroid effects leave on different types of rock," says the expert. .
"It is also clear that the appropriate work for the acquisition of remote sensing data (satellite imagery, aerial imagery, geophysics) is a great help when you want to study impact structures covered under some kind of material, in this particular case, ice."
Tobar notes this This work should be supplemented with field visits where scientists with knowledge in planetary geology should gather evidence in hand samples, "That is, examples of rocks with typical structures produced by the effects, which will be analyzed later in the laboratory, with the ultimate goal of merging key evidence on various scales: mega, macro and microscopic, a work that lasts years and should not be done lightly.