An ice survey in Greenland found evidence suggesting the impact of an iron asteroid one kilometer wide on that island, perhaps only 12,000 years ago.The 30-kilometer-wide crater resulting from the collision remained hidden for a while under a layer of 800-meter-thick ice.
It was recently exposed by an ultra-wideband radar system developed at the Remote Ice Shelf Detection Center (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 remote northwest of Greenland, are detailed in an article published in the journal Science Advances.
It was identified with data collected between 1997 and 2014 by the KU for the NASA Regional Arctic Climate Assessment Program and the IceBridge operation and was complemented with more data collected in May 2016 using coherent multi-channel probe radar. (MCoRDS) developed in KU.
"We collected a great deal of radar research data over the last two decades, and glaciologists gathered this information to produce maps of how Greenland is under ice," says co-author John Paden, associate professor of electrical engineering and science . Computing at KU and associate scientist at CReSIS.
"Danish researchers were looking at the map and saw this large, crater-like depression below the ice sheet and watched satellite images, As the crater is at 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, state-of-the-art 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-altitude flights in a grid pattern over the impact crater to detail its dimensions.
"You can see the rounded structure at the edge of the ice sheet, especially when you fly high enough," he says. For the most part, the crater can not be seen through the airplane window. Using satellite imagery taken at a low angle of sunshine that accentuates the hills and valleys on the ice sheet terrain, you can actually see the entire crater circle in these images. "
To confirm satellite and radar discoveries, the research team conducted additional studies of the glaciopluvial soil of the larger river that drained the crater. The work showed the presence of "impacted quartz and other impact-related grains", such as glass. The research team believes that these rocks and vitreous grains will probably be produced from the impact melting of the grains on the parent metal rock.
Determine impact date
The work continues to more accurately determine the momentum of the asteroid's impact on Greenland. The authors say that there is evidence suggesting that the Hiawatha impact crater was formed during the Pleistocene, since this age is more consistent with the inferences from the data currently available. However, even this wide time gap remains "uncertain". Southwest of the crater, the team found a region rich in potential debris ejected from the impact, which could help reduce the range of dates.
"This would have projected 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 freshwater in the Strait of Nares between Canada and Greenland that would have affected the ocean flow in that region, . all evidence, "Paden argues. Evidence indicates that the impact probably occurred after the formation of the Greenland 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 preserve 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 kind of material that asteroid impacts leave on different rock types," says the expert. .
"In the same way," he continues, "it is clear that the work corresponding to the acquisition of remote sensing data (satellite images, aerial photographs, geophysics) is of great help when one wants to study impact structures covered by some kind of material in this particular case, ice. "
Tovar points out that this work should be complemented with field visits in which scientists with knowledge in planetary geology must collect evidence on hand samples, "That is, rocks samples with typical structures produced by impacts, which will be later analyzed in the laboratory, with the final objective of amalgamation of key evidence at different scales: mega, macro and microscopic. A work that takes years and should not be done lightly. "