Scientists have—totally by accident—come across a hidden canyon that dwarfs the Grand one, the BBC reports. The researchers were using radar to map out Greenland's bedrock when they stumbled upon the 2,625-foot deep feature, which, at 500 miles, is longer than the Grand Canyon's 277 miles, Design & Trend notes. It's full of ice now—the stuff is up to two miles thick—but a river forged the canyon some four million years ago, predating the ice.
Now, a little meltwater drains out of the northern end of the unseen canyon, which runs from central Greenland to its north coast. "With satellite images instantly available on a mobile phone we could assume that the Earth has been fully mapped, but there's clearly a lot left to discover," says a scientist. The canyon could also be bad news: Water moving under Greenland's ice could contribute to faster melting, the Christian Science Monitor notes. So are there more of these in the world? The lead researcher tells National Geographic he's now wondering what lies under the Antarctic Ice Sheet—which is 10 times the size of Greenland's.