Mars sand dunes may hint at water beneath
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.
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NASA's small squadron of Mars orbiters revealed dunes in the planet's north polar regions, and they took enough images over a sufficient period of time to reveal that the dunes moved. But the pace was glacial, especially when compared with the movement of dunes in locations such as the Sahara Desert or the US Southwest.Skip to next paragraph
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Dinwiddie and colleagues looked to the Great Kobuk Sand Dune field for possible answers as to why Mars' polar dunes were such geophysical sloths – first exploring the Alaskan analogues via satellite remote-sensing, then in 2010, with a field trip in March, while temperatures still averaged about 5.5 degrees Fahrenheit and the dunes' top, mobile layer was still frozen solid.
During the field trip, the researchers noticed water coming up through the bore holes they had drilled but that had not yet reached deep into the dunes to tap the region's aquifer. Ground-penetrating radar and measurements of the ground's electrical resistance revealed evidence for a layer of liquid water just below the frozen mobile layer.
As if to ice the cake, the team found water seeping out of mini bluffs where erosion or slumping exposed this layer to the increasing warmth of a March sun. They also found debris flows, which appeared to signaled brief bouts of melting from this layer.
Intriguingly, climate conditions for the Great Kobuk Sand Dune field in March are similar to the conditions NASA's Mars Rover Curiosity is experiencing at Gale Crater – which also has dunes. They migrate at a lethargic pace comparable to Alaska's dunes. But they don't get the seasonal frost cover that Alaska's or Mars' polar dunes do.
At the least, the mechanism generating the debris flows on Alaska's dunes could help explain seasonal debris flows researchers have detected on Mars, notes Dr. Hooper.
Since the first evidence for these flows was reported 13 years ago, researchers have debated the triggers. Some argue that they merely represent an avalanche of sediment that the slopes no longer could support. Others have suggested they are triggered by sudden outbursts from buried CO2 ice that rapidly turns to gas and punches through the soil and rock on slopes when sunlight warms them. Or they could result from the sudden release of water as the sunlit warmth of surrounding soils melts enough ice to trigger a large flow before the water quickly evaporates.
Flows that researchers have seen on the walls of Martian craters appear and disappear with the warm season, Dr. Hooper notes, just as "flow features commonly form under seasonally warming conditions" at the Great Kobuk Sand Dunes.
"By studying cold-climate dune fields on Earth, we will achieve a greater understanding of the full spectrum of possible origins for Martian gully systems," he writes in an email.
"Martian debris flows and their associated gullies are believed to be youthful geologic features," he adds. They serve as "a reminder that Mars is not a dead planet but still has active surface processes."
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