Greenland is hiding an explosive secret under its thick ice sheet.
In 2015, researchers created a new map of the continent's bedrock, which is normally obscured by thousands of feet of ice. When an international team of scientists studied that map, they found a 16-mile-wide, bowl-like depression - it looked like a giant asteroid impact crater.
The scientists wanted to be sure, though, since this would be the one of the 25 largest impact craters on Earth. So they shored up evidence for the claim over the next three years.
In a study published Wednesday in the journal Science Advances, the team reports that there is indeed a crater, which was made by a half-mile-wide iron asteroid slamming into Greenland between 12,000 and 3 million years ago.
Here's how the group made this remarkable discovery - and why it should worry us today.