An enormous crater believed to have been caused by an asteroid that slammed into Earth 12,000 years ago has been found beneath the ice in Greenland.
The 19-mile-wide impact had remained hidden under a half-mile-thick sheet of ice until it was exposed by a state-of-the-art radar system at the University of Kansas.
Located under the Hiawatha Glacier in remote northwest Greenland, the crater is thought to be the result of an iron asteroid about one kilometre in size that struck the island at the end of the Pleistocene.
The Pleistocene period – beginning about 2.6 million years ago and lasting until about 11,700 years ago – included the final ice age, during which huge glaciers covered the surface of the planet.
It took almost two decades to identify the crater, with most of the data needed collected between 1997 and 2014, and the findings have now been detailed in a new paper for the latest edition of Science Advance.
Co-author John Paden, a professor of electrical engineering and computer science at the University of Kansas, said: "We've collected lots of radar-sounding data over the last couple of decades, and glaciologists put these radar-sounding data sets together to produce maps of what Greenland is like underneath the ice.
"Danish researchers were looking at the map and saw this big, crater-like depression under the ice sheet and looked at satellite imagery and – because the crater is on edge of the ice sheet – you can see a circular pattern there as well.
"The two combined made a really strong case for this being an impact-crater site."
Based on the discovery, the catchily-named Multichannel Coherent Radar Depth Sounder (MCORDS) – built for the university by the Alfred Wegener Institute in Germany – began its survey in May 2016.
Once the radar system had done its bit, a research team carried out its own surveys on the ground.
Work still needs to be done to determine the precise timing of the asteroid impact, and the discovery of possible debris southwest of the site could help to narrow the date range.
Professor Paden explained: "There would have been debris projected into the atmosphere that would affect the climate and the potential for melting a lot of ice.
"So there could have been a sudden freshwater influx into the Nares Strait between Canada and Greenland that would have affected the ocean flow in that whole region.
"The evidence indicates that the impact probably happened after the Greenland ice sheet formed, but the research team is still working on the precise dating."
Professor Paden was just one of a large but exclusive team of researchers who worked to reveal the impact crater, with colleagues from the University of Copenhagen among those to assist the project.
He admitted that he was excited to finally publish the findings.
More from Science & Tech
"It was really cool – it was the kind of thing where I went home and told my kids about it," Professor Paden said.
"It's one of those fun moments. They were impressed. A lot of times, my research isn't that interesting to them, but this impact crater was something they could connect to."