Deep beneath the surface of Greenland's ice sheet lies a chasm half a mile deep and longer than the Grand Canyon. According to a paper published in Science, radar data from NASA's IceBridge project — which measures changes in polar ice from aircraft — has revealed the existence of the hitherto-unknown canyon. Part of IceBridge's mission is to measure ice thickness, using frequencies that can bounce through ice to the bedrock beneath. When data from IceBridge and previous studies was put together, it revealed a canyon 460 miles long and 2,600 feet deep; by comparison, the Grand Canyon is 277 miles long, its deepest point 6,000 feet below the rim.

The newly discovered canyon is thought to have formed before ice covered Greenland, and it looks like a river channel, like the Grand Canyon. As much as four million years ago, the canyon could have held a major river system that flowed from the center of Greenland to the coast. Now, of course, it's not visible to the naked eye, buried under an ice sheet that can be miles thick. But the canyon could still be shifting water around the island. Lead author Jonathan Bamber and his team believe that the canyon funnels meltwater under the glacier out to the ocean, stopping it from lingering beneath the ice sheet and making it "slippery." And that, in turn, could actually make it harder for the ice sheet to slip into the sea, delaying in some small part the rising sea levels that come with climate change.