A Valley Network of Drainage

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    Many systems on Mars show a resemblance to drainage systems on Earth, where
water acts at slow rates over long periods of time. As on Earth, the channels shown
here merge together to form larger channels. However, these valley networks are less
developed than typical terrestrial drainage systems, with the Martian examples lacking
small-scale streams feeding into the larger valleys. Because of the absence of small-scale
streams in the Martian valley networks, it is thought that the valleys were carved
primarily by  ground water flow rather than by runoff of rain. Although liquid water is
currently unstable on the surface of Mars, theoretical studies indicate that flowing
groundwater might be able to form valley networks if the water flowed beneath a
protective cover of ice. Alternatively, because the valley networks are confined to
relatively old regions of Mars, their presence may indicate that Mars once possessed a

warmer and wetter climate in its early history. (Image Credit: Calvin J. Hamilton;
Caption: LPI)

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