A vast, previously unrecognised canyon system could be hidden under the Antarctic ice sheet.
Hints of its presence are seen in the shape of the white continent's surface, in a largely unexplored region called Princess Elizabeth Land.
If confirmed by a proper geophysical survey - now under way - the winding canyon network would be over 1,000km long and in places as much as 1km deep.
These dimensions would make it bigger than the famous Grand Canyon in the US.
"We know from other areas of Antarctica that the shape of the ice surface is obviously dependent on the shape of the landscape underneath - because the ice is flowing over that landscape," explained Dr Stewart Jamieson, from Durham University, UK.
"When we look in Princess Elizabeth Land with satellite data, there seem to be some linear features in the surface ice that to us look very reminiscent of a canyon.
"We have traced these faint lineations from the centre of Princess Elizabeth Land all the way to the coast, off to the north. It's a pretty substantial system," he told BBC News.
There are suggestions also that the canyon network is connected to a previously undiscovered subglacial lake.
If confirmed, this lake would likely cover up to 1,250 square km, which is about 80 times as big as Windermere, England's largest lake.
The initial interpretation of a canyon system is supported by radar data that has been gathered in a couple of locations.
Radar sees through the ice layers to the hard rockbed below.
The story is consistent, says team-member Prof Martin Siegert, from Imperial College London, UK, said.
"Discovering a gigantic new chasm that dwarfs the Grand Canyon is a tantalising prospect.
"Geoscientists on 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."
Most of Antarctica has now been covered by full geophysical surveys that have imaged the continent's underlying topography.
But there remain two "Poles of Ignorance" that need to be filled in. One of these is Princess Elizabeth Land; the other is the Recovery Basin.
Both are in East Antarctica, and both are now the targets of intense study.
International teams - comprising scientists from the US, the UK, Australia, China and other nations - are flying sensors back and forth across thousands of square kilometres of ice surface.
When complete, Antarctic researchers will have a comprehensive view of what the landscape really looks like beneath all its accumulated ice. This is fundamental knowledge in trying to understand how the continent might react in a warming world.
"If we don't know the shape of the rockbed, we cannot confidently build models that will produce sensible behaviours in the ice," asserted Dr Jamieson.