Photo: NASA discovers a crater beneath the Greenland Ice Sheet

This image from NASA shows how an aerial survey of northwestern Greenland uncovered evidence that a kilometre-wide iron asteroid slammed into the island, perhaps as recently as 12,000 years ago. The resulting 30-kilometre-wide crater has remained hidden under the thick ice sheet until now. It was exposed by an ultra-wideband chirp radar system developed at the Center for the Remote Sensing of Ice Sheets. This illustration shows the aircraft sending radar waves through the ice. (IMAGE COURTESY OF NASA)