The discovery, based on research in Alaska, opens a window on processes at play early in Mars' history, when it hosted an environment that could have harbored microbial life.
Shifting dunes on Mars, especially those near the planet's north pole, may harbor layers of liquid water not far beneath their ice-encrusted surfaces.
That is the implication of studies of sand dunes in Alaska's Kobuk Valley National Park, some 380 miles northwest of Fairbanks. There, above the Arctic Circle, researchers using the dunes as stand-ins for dunes on Mars have found evidence for liquid water trapped between the dunes' icy winter coat and subsurface layers of ice or freeze-dried silt that form a temporary, cement-like barrier that prevents the water from percolating deeper into the dune.
The water remains liquid because it exists in an environment of temperature and pressure that allows liquid water, ice, and water vapor to exist side by side.
The discovery of this seasonal mechanism for storing liquid water on Mars-like features at Mars-like temperatures opens a window on processes that could have been at play early in Mars' history, when it hosted an environment that could have harbored microbial life.
And it could help explain debris flows scientists have spotted on sunlit sections of crater and canyon walls in various locations around the planet.
"Mars has likely had active sand dunes during every geologic era, and some of these eras were warmer and wetter than Mars is today," notes Cynthia Dinwiddie, a researcher with the Southwest Research Institute in Boulder, Colo.
"There is some possibility that equivalent processes are currently occurring on Mars," primarily in dune fields in Mars' equivalent of the Arctic, she writes in an email. Still, "the likelihood is even greater that equivalent processes occurred on ancient Mars."