A mile-wide iron asteroid hit the Hiawatha glacier perhaps as recently as 12,000 years ago. The resulting impact crater 19.3 miles wide has remained hidden under a half-mile-thick ice sheet until now

A mile-wide iron asteroid hit the Hiawatha glacier perhaps as recently as 12,000 years ago. The resulting impact crater 19.3 miles wide has remained hidden under a half-mile-thick ice sheet until now