An ice study in Greenland has found evidence showing the impact of a one kilometer iron asteroid on the island, probably only 12,000 years ago.The crater produced from a collision, 30 kilometers wide, remains hidden for now under an 800 meter thick layer of ice.
It was recently exposed by the ultra-wideband radar system developed at the Center for Remote Detection of Ice Platforms (CReSIS), based at the University of Kansas (KU), in the United States. Characteristics of the crater, the result of the impact under the Hiawatha glacier in the remote northwest of Greenland, detailed in articles published in & # 39; Progress of Science. & # 39;
It was identified with data collected between 1997 and 2014 by KU for the Nasa Program for Regional Arctic Climate Assessment and IceBridge operations, and supplemented with more data collected in May 2016 using a coherent multichannel radar probe. depth (MCoRDS), developed at KU.
"We have collected a large amount of radar survey data over the past two decades, and glaciologists are gathering this information to produce a map of what Greenland is under ice," said co-author John Paden, professor of electrical and science engineering. Computing in KU and associate scientists at CReSIS.
"Danish researchers looked at the map and saw this great depression, similar to a crater, under the ice sheet and observing satellite imagery, 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 study was carried out using a new state-of-the-art radar designed and built by KU for the Alfred Wegener Institute in Germany, "he added.
Paden, who helped develop MCoRDS radar signal processing software, participated in low altitude flights in grid patterns above the impact crater for detailed dimensions.
"You can see the round structure on the edge of the ice sheet, especially when you fly high enough," he said. For the most part, the crater cannot be seen through the aircraft window. By using satellite imagery taken with a low sun angle that accentuates hills and valleys on the plains of the ice sheet, you can really see the entire circle of craters in these images. "
To confirm satellite and radar findings, the research team conducted further research on glaciofluvial deposits from a larger river that dried the crater. The work shows the existence of "impacted quartz and other items related to impact", such as glass. The research team believes that these stones and vitreous grains are likely to result from fusion of grain impacts in metasedimentary host rocks.
Determine the date of impact
Work continues to determine more precisely the moment of impact of asteroids in Greenland. The writers say that there is evidence to suggest that the impact craters of Hiawatha were formed during the Pleistocene, because this age is more consistent with the conclusions of the data currently available. However, even this wide range of time remains "uncertain". In the southwest of the crater, the team has found an area that is rich in potential debris that is ejected from collisions, which can help reduce the date range.
"It will project debris into the atmosphere that will affect the climate and the potential to melt a lot of ice, so there may be a sudden flow of fresh water in the Nares Strait, between Canada and Greenland, which will affect the sea flow in the region. "Paden argued. Evidence shows that the impact may occur after the Greenland ice sheet is formed, but the research team is still working on the exact date. "
According to planetary geologist David Tovar, the discovery of a crater in Greenland shows that there are several regions on this planet that can still maintain evidence of the existence of craters. "Many times, this structure is not taken into account by geologists because of a lack of knowledge about their training process and the types of materials that carry asteroid impacts on various types of rocks," said the expert. .
"Likewise," he continued, "it is clear that work in accordance with the acquisition of remote sensing data (satellite imagery, aerial photography, geophysics) is very helpful when you want to study the impact structures included in some types of material; in this particular case, ice."
Tovar shows that this work must be supplemented by a field visit where scientists with knowledge in planetary geology must gather evidence in hand samples, "That is, rock samples with distinctive structures produced by impacts, which will be analyzed in the laboratory, with the ultimate goal of combining key evidence at different scales: mega, macro and microscopic. Work that takes years and cannot be done easily. "