And you thought that gazing over the edge of the Grand Canyon was spectacular. An analysis of satellite data has revealed what scientists believe may be an even bigger chasm–the world’s largest canyon, in fact–hidden beneath the Antarctic ice sheet.

The startling finding is revealed in an article being published this month in the journal Geology, by a team that includes researchers from the UK’s Dunham and Newcastle universities and Imperial College London.

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The previously unknown canyon winds through Princess Elizabeth Land in east Antarctica, a largely unexplored area, and is buried under a layer of ice that’s more than a mile deep. The canyon is believed to be more than 621 miles long and in places as much as 3,280 feet deep. That would make it more than twice as long as the Grand Canyon, which stretches for 277 miles. The American landmark’s average depth of one mile still is more than the Antarctic canyon.

In a press release, Martin Siegert, a professor at the Grantham Institute at Imperial College London,called the discovery “tantalizing,” but cautioned that further research will be needed to validate the discovery.

“Geoscientists in Antarctica are carrying out experiments to confirm what we think we are seeing from the initial data, and we hope to announce our findings at a meeting of the ICECAP2 collaboration, at Imperial, later in 2016,” he said.

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The researchers believe that the landscape beneath the ice sheet has probably been carved out by water. They say it is either so ancient that it existed before the Antarctic ice sheet covered the area, or it was created by water flowing and eroding the rocks beneath the ice.

The findings suggest that the canyon may be connected to a previously undiscovered sub-glacial lake, which could be nearly 780 square miles in area.