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| Water on Mars came from within |
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9 March 2007, for Nature Network Boston How vast deposits of salt ended up on Mars’s surface is a long-standing mystery, but MIT researchers appear to have solved it. Their new computer model suggests that the salts came from water seeping up from stores of groundwater and then evaporating from the planet’s surface. A wide range of evidence suggests that Mars was a warm and wet planet more than three billion years ago. But some of that evidence, such as the salt deposits, raises further questions about what form the water took—oceans or streams or underground reservoirs. In particular, researchers have puzzled over the Meridiani Planum, a large, flat plain with salt deposits 200 to 800 meters thick. In order for an evaporating sea to leave behind that much salt, it would have to have been more than two kilometers deep—but the plain doesn’t lie in a basin where water could accumulate.
Instead, the new research suggests, the salts came from water percolating up from the ground. In Nature this week, Jeffrey Andrews-Hanna and Maria Zuber of MIT, along with Roger Phillips of Washington University in St. Louis, describe their new model, which shows how water could flow through porous rocks in Mars’s crust. That water could have accumulated high concentrations of salts as it traveled through thousands of miles of rock before leaking out onto the plain. Small amounts of water seeping up over many years could thus leave behind as much salt as the evaporation of a huge sea. |
Mars’s Meridiani Planum, as seen by