A scar beneath the ice
Hidden beneath nearly a kilometer of ice at the margin of the Hiawatha Glacier lies a massive impact crater, first identified in 2015 from airborne radar surveys. Data from NASA's Operation IceBridge and Germany's Alfred Wegener Institute revealed a circular bedrock depression 31 kilometers (19 miles) wide and about 320 meters (1,050 feet) deep. It is one of the 25 largest impact craters found on Earth. The structure is remarkably well-preserved, with a distinct elevated rim and a subtle central uplift, features of large complex craters.
The discovery was confirmed by analyzing sediments washed out from under the glacier. Field teams from the Natural History Museum of Denmark collected samples from the river draining the crater, which contained proof of a violent impact. These samples included shocked quartz grains, whose crystal structures are deformed in a specific way that only occurs under the immense pressure of an asteroid strike. Geochemical analysis of the sediment also identified the projectile: a fractionated iron asteroid, estimated to have been at least 1.5 kilometers (nearly a mile) wide. The energy released by this impact would have been millions of times greater than an atomic bomb.