series of newly discovered depressions on the Martian surface could be the entrances to a cave system on the red planet.
Hints of subsurface tunnels have been found in images of Mars before, but the new evidence is more suggestive, said Glen Cushing, a physicist with the U.S. Geological Survey who discovered the possible caves.
Such a subsurface system could provide shelter to future Mars-visiting astronauts, as well as a protective habitat to any potential past or present Martian microbes, Cushing said.