A series of aerial radar images, obtained this past Christmas by U.S. and Chinese researchers, has revealed a new addition to Antarctica’s sizable complement of subglacial lakes.

It’s quite large, about 12,000 sq/km (7,400 sq/mi). For comparison, New York state is 87,800 sq/km (54,500 square mi) . And the lake has likely been entombed within the unfathomably ancient Antarctic ice cap for millions of years. Scientists are uncertain whether the feature is actually a subglacial lake—akin to the more famous lakes Vostok and Ellsworth—or a semi-frozen slurry of sediment.

The feature, located in the remote Princess Elizabeth Land of East Antarctica, must await a future expedition during the coming southern summer to elucidate more of its hidden mysteries.

If the feature really is a sediment slurry, it will furnish climate scientists with a window onto the past climatic regimes that have shaped the present state of the Antarctic continent—and thus, by extension, provide more information about the Earth’s changing weather patterns.

If it’s a lake, then it means another pristine, uncontaminated environment that has been wholly free of external biological and evolutionary influences for uncounted millions of years. It means an important terrestrial analogue to those subsurface aqueous environments astronomers suspect may be lurking in the outer Solar System—beneath the surface of Europa and Enceladus, for instance.

But what’s actually down there? We’ll have to wait until next Christmas to find out.