At 8:25 p.m. Moscow time on Sunday, drillers hit lake water at a depth of 12,355 feet (3,766 meters)—making them the first ever to probe a subglacial lake, according to a statement provided by Russia's Arctic and Antarctic Research Institute.

That's because the Russian scientists recorded an increase in pressure at the bottom of the borehole—an "obvious clue" that they broke through the ice.

"There's no other reason you would run into a pressure kick like that unless you'd broken into a seal, which would be the surface of the lake," said Kennicutt, who is also the president of the nonprofit Scientific Committee on Antarctic Research.

This "should be celebrated," Kennicutt emphasized. "Fifteen years ago we couldn't imagine