Greenland crater renewed the debate over an ancient climate mystery
Scientists disagree on what the find means for a controversial comet-impact hypothesis
BIG REVEAL Ice-penetrating radar disclosed a possible crater under a Greenland glacier. This topographic map strips away the ice to show the 31-kilometer-wide crater.
Natural History Museum of Denmark, Cryospheric Sciences Lab/NASA Goddard Space Flight Center
For three years, a team of scientists kept a big secret: They had discovered a giant crater-shaped depression buried beneath about a kilometer of ice in northwestern Greenland.