Sea ice surrounding the continent expands outward, effectively doubling Antarctica's size. But during the winters of 2016 and 2017, a rare hole called a polynya opened in the middle of the sea ice — one about the size of Switzerland. And scientists have just now figured out how it came to be.

Scientists first discovered the mysterious hole in the 1970s, but questions have remained about how it formed.

The Maud Rise polynya has been sporadically opening up in Antarctica's ice since at least the 1970s. Now climatologists finally know why.

Every now and then for the last 50 years, an enormous hole opens up in the Antarctic sea ice. And by enormous, we mean truly enormous — the feature in question was twice the size of Wales last time it appeared in 2016 and 2017.