While flying over the eastern Beaufort Sea as part of NASA’s Operation IceBridge, mission scientist John Sonntag made photos of something he had never seen before on April 14: odd crater-like holes in the ice.

While experts agree the sea ice in the photograph is thin and likely young, since it is a grey color (indicating there is little snow), what made the holes is a mystery. “I have never seen anything like that before,” said IceBridge project scientist Nathan Kurtz. (See what the world would look like if all the ice melted.)

Now in its tenth year in the Arctic, Operation IceBridge is an airborne mission flown annually over both polar regions using various instruments to measure the