Mars' Architect-in-Chief? Water, Says Study
Discovery News
August 25, 2008
Scientists are moving closer to a unilateral opinion that water, even in relatively modern times, exists on Mars. The latest finding offers a detailed scenario of how small channels appear on the planet's face despite what appears to be a complete lack of surface water.
Eight years ago, a satellite made a second pass over a patch of Mars and set scientists abuzz with pictures showing small channels where none were seen before.
That got people thinking about how water could exist on the dry, frozen surface of Mars long enough to etch its face. Other researchers credited the gully-like features to bursts of carbon dioxide seeping out of the ground.
"We think that these are really exciting results because they establish a link between recent gullies and major recent (last few millions of years) large accumulations of ice," Brown University's James Head wrote in an e-mail to Discovery News.
Armed with new pictures from a next-generation spacecraft and a painstaking reconstruction of climate change on Mars, a team of scientists this week painted a time-lapse view of gully formation that again fingers water as architect-in-chief.
Head and his colleagues studied a 6.6-mile diameter crater, located at about 40 degrees south latitude, the most common location for gullies on Mars.
The story they pieced together, detailed in today's issue of the Proceedings of the National Academy of Sciences, describes how accumulations of snow and ice on the crater's north wall produced glaciers that slowly slipped to the crater's floor, transporting bits of rock and debris. As temperatures warmed, due to seasonal changes, the ice sublimated into a gas, leaving behind the depressions.
"It's like taking an ice cube and covering it with a layer of sand. The sand is going to keep the underlying ice cold a bit longer," said Boston University Earth Sciences researcher David Marchant, a co-author of the paper who became interested in Mars after studying climate change and ice formations in the cold, dry deserts of Antarctica.
More recently, the depressions caught wind-blown bits of snow and ice, which melted, carving out the gullies, the scientists suggest.
"There is still a lot of snow and ice accumulating, and therefore a very high likelihood of melting and water flow to form gullies," Head said.
The authors discount prior hypotheses that dry avalanches or surges of groundwater formed the gullies.
"We think that dry avalanches are unlikely to be the major factor because we see such obvious evidence of the presence of ice and snow, even today," Head said.
"The groundwater release seems unlikely, because groundwater would be at greater depths, and if you had enough melting to get down to such depths, you would have to start with the near-surface snow and ice," he added.
Jonathan Lunine, a University of Arizona planetary science researcher, said that the discovery of different types of gullies and the fact that they were widespread on Mars lessens the probability that underground bursts of carbon dioxide had carved the gullies.
"It doesn't mean it's liquid water," he told Discovery News. "It could be other things."
Additional imagery from the Mars Reconnaissance Orbiter, which can reveal details of objects as small as a boulder, combined with chemical data should help scientists unravel more of the mystery.
"When you've got this flood of data, it's going to take a while to sift through," Lunine said.
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