An international team of researchers has unearthed a large meteorite impact crater under more than a half-mile of ice in northwestern Greenland's Hiawatha Glacier.
Measuring roughly 1,000 feet deep and more than 19 miles in diameter, the crater -- the first of any size found under the Greenland ice sheet -- is one of the 25 largest impact craters on Earth, the researchers said.
According to the study, published in the journal Science Advances, the crater formed less than 3 million years ago when an iron meteorite more than half a mile wide smashed into northwest Greenland.
The resulting depression was subsequently covered by ice.
"The crater is exceptionally well-preserved and that is surprising because glacier ice is an incredibly efficient erosive agent that would have quickly removed traces of the impact," said lead author Kurt Kjaer, Professor at the Natural History Museum of Denmark.
The tectonic structures in the rock near the foot of the glacier as well as the samples of sediments washed out from the depression confirm that the glacier is a meteorite crater.
"Some of the quartz sand coming from the crater had planar deformation features indicative of a violent impact; this is conclusive evidence that the depression beneath the Hiawatha Glacier is a meteorite crater," explained Nicolaj Larsen, Associate Professor at Aarhus University in Denmark.
In July 2015, the scientists first noticed an enormous, previously unexamined circular depression under Hiawatha Glacier, sitting at the very edge of the ice sheet in northwestern Greenland.
Using NASA's Terra and Aqua satellites, they examined the surface of the ice in the Hiawatha Glacier region and quickly found evidence of a circular pattern on the ice surface that matched the one observed in the bed topography map.
In May 2016 they mapped the crater and the overlying ice over the Hiawatha Glacier.
"The survey imaged the depression in stunning detail: a distinctly circular rim, central uplift, disturbed and undisturbed ice layering, and basal debris - it's all there," said Joe MacGregor, a NASA glaciologist at Goddard Space Flight Center in Maryland.
Kjaer noted that the crater's condition indicates that the impact might even have occurred toward the end of the last ice age, which would place the resulting crater among the youngest on the planet.