Researchers at Brown University have shown that some Martian
valleys appear to have been caused by runoff from orographic precipitation —
moisture carried part of the way up a mountain and deposited on the slopes.
Valley networks branching across the Martian surface leave
little doubt that water once flowed on the Red Planet. But where that ancient
water came from — whether it bubbled up from underground or fell as rain or
snow — is still debated by scientists. A new study by researchers at Brown
University puts a new check mark in the precipitation column.