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    Snowmelt May Have Caused Martian Valleys

    Water-carved valleys on Mars appear to have been caused by runoff from precipitation, likely meltwater from snow. Early Martian precipitation would have fallen on mountainsides and crater rims.
    Water-carved valleys on Mars appear to have been caused by runoff from precipitation, likely meltwater from snow. Early Martian precipitation would have fallen on mountainsides and crater rims.

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    Ancient runoff from melting snow may have been the cause for many of the valleys branching across Mars.

    Researchers at Brown University believe many of the valleys were created runoff of what they call “orographic precipitation” -- when warm, humid air is pushed up a mountain and deposits rain or snow.

    The source of Martian water has long been debated among scientists, with some thinking the water may have bubbled up from underground. The new study makes the case for precipitation. 

    Researchers looked at four areas along tall Martian mountain ridges or raised crater rims.

    They then had to make a theoretical model to assess the direction of the prevailing winds in the ancient Martian atmosphere. The model simulated air movement based on the gas composition of Martian air. Once that was established the research team created a model to predict the where precipitation was likely to have fallen.

    According to the models, the precipitation would have been heaviest at the heads of the most dense valley networks.

    “Their drainage density varies in the way you would expect from the complex response of precipitation to topography,” said Kat Scanlon, a geological sciences graduate student at Brown who led the research. “We were able to confirm that in a pretty solid way.”

    The models indicated a climate cold enough to cause the precipitation to be snow, but the researchers said periodic warming conditions could have caused episodic rain.

    “The next step is to do some snowmelt modeling,” said Scanlon. “The question is how fast can you melt a giant snow bank. Do you need rain? Is it even possible to get enough discharge [to carve the valleys] with just the snowmelt?”

    The research was published in the Geophysical Research Letters.

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