Valley networks suggest ancient snowfall on Mars

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. The findings help to answer the question of whether water flowing on ancient Mars bubbled up from the ground or fell down from the atmosphere.

Fuente : http://www.eurekalert.org/pub_releases/2013-07/bu-…