An ice research in Greenland has revealed evidence suggesting the impact of an asteroid of iron a kilometer on that island, perhaps only 12,000 years ago.The crater resulting from the collision, 30 kilometers wide, was hidden for the moment under an ice layer of 800 meters thick.
It was recently exposed by an ultra-wide-band radar system developed at the CRSSIS, based in Kansas University (KU), in the United States. The features of the crater, the result of the impact of the Hiawatha glacier in northwest Greenland, are detailed in an article published in "Science Advances".
It was identified with data collected by KU between 1997 and 2014 for the NASA Arctic Climate Assessment and IceBridge operation, and was supplemented with more data collected in May 2016 using consistent coherent multi-axis radar. (MCoRDS), developed in KU.
"We have collected a large amount of radar data over the past two decades, and glaciologists have gathered this information to produce maps of what Greenland is under ice," says co-author John Paden, associate professor of electrical engineering and science. Calculation in KU and associate scientist in CReSIS.
"The Danish scientists looked at the map and saw this great depression, similar to a crater, under the ice sheet and noticed satellite images and, Because 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 survey was conducted using a new state-of-the-art radar designed and built by KU for the Alfred Wegener Institute in Germany, "he adds.
Paden, who contributed to the development of MCoRDS radar signal processing software, participated in low altitude flights in a network model over the impact crater to detail its dimensions.
"You can see the rounded structure at the edge of the ice sheet, especially when you're flying tall," he says. For the most part, the crater can not be seen through the airplane window. Using satellite images made with a small angle of sun that accentuates the hills and valleys in the ice sheet field, you can really see the circle of the entire crater in these images. "
To confirm the satellite and radar findings, the research team conducted additional field studies on the glaciofluvial sediment of the larger river that drained the crater. The paper has shown the presence of "affected quartz and other impact beans" such as glass. The research team believes that these rocks and grains are likely to be produced by merging the impact of the beans into metamedimentary mother rock.
Determine the impact date
The work continues to determine the exact moment of the asteroid impact in Greenland. The authors say this there is evidence that the impact crater Hiawatha was formed during the Pleistocene, as this age is more consistent with the currently available data. However, even this wide range of time remains "uncertain". The southwest of the crater, the team found a region rich in potential expelled impact scams, which could help reduce the date range.
"It would have designed debris in 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 have affected the oceanic flow in that region whole, "Paden argues. The evidence shows that the impact probably arose after the formation of Greenland's ice sheet, but the research team is still working on the exact date. "
According to planetary geologist David Tovar, the discovery of the crater in Greenland shows that there are several regions of the planet that can still keep evidence of impact craters. "Often, these structures are not taken into account by geologists because of the lack of knowledge about their training processes and the type of material that the asteroid impacts on different types of rock," says the expert. .
"Similarly, it is obvious that the job of acquiring remote sensing data (satellite imagery, aerial photographs, geophysics) is of great help when you want to study the impact structures that are covered by a certain type of material, in which case especially ice. "
Goods show this this work should be complemented by field visits in which scientists with knowledge in planetary geology should collect evidence in hand samples, "That is, specimens of rock with impact-generating structures, which will then be analyzed in the laboratory, with the ultimate goal of amalgamating key evidence on different scales: mega, macro and microscopic. A job that lasts for years and should not to be done easily. "