"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. Related Links: |
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