LIQUID WATER
ON MARS
26. Valley Network (42°S,92°W)
Unlike the features shown in slides #23–#25,
many valley systems on Mars do not show evidence for catastrophic flooding.
Instead, they show a greater resemblance to drainage systems on Earth,
where water acts at slow rates over long periods of time. The valleys
in this image are much smaller than the channels shown in slides
#23–#25. 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 groundwater flow rather than by runoff of rain. Although
liquid water is currently unstable on the surface on 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 on
Mars, their presence may indicate that Mars once possessed a warmer
and wetter climate in its early history. The area shown is about 200
kilometers across.
From
Mars Digital Image Map, image processing by Brian Fessler, Lunar and
Planetary Institute
Right
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