Geoscience Reference
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Baikal. Lakes that were fed by valley networks are found in the southern highlands.
There are places that are closed depressions with river valleys leading into them.
These areas are thought to have once contained lakes; one is in Terra Sirenum which
had its overflow move through Ma'adim Vallis into Gusev Crater, explored by the
Mars Exploration Rover Spirit. Another is near Parana Vallis and Loire Vallis. Some
lakes are thought to have formed by precipitation, while others were formed from
groundwater. Lakes are estimated to have existed in the Argyre basin, the Hellas
basin, and maybe in Valles Marineris. It is likely that at times in the Noachian, very
many craters hosted lakes. These lakes are consistent with a cold, dry (by Earth
standards) hydrological environment somewhat like that of the Great Basin of the
western USA during the Last Glacial Maximum.
Research from 2010 suggests that Mars also had lakes along parts of the equator.
Although earlier research had showed that Mars had a warm and wet early history
that has long since dried up, these lakes existed in the Hesperian Epoch, a much
later period.
Using detailed images from NASA's Mars Reconnaissance Orbiter, the
researchers speculate that there may have been increased volcanic activity, meteorite
impacts, or shifts in Mars' orbit during this period to warm Mars' atmosphere
enough to melt the abundant ice present in the ground.
Volcanoes would have released gases that thickened the atmosphere for a
temporary period, trapping more sunlight and making it warm enough for liquid
water to exist. In this study, channels were discovered that connected lake basins
near Ares Vallis. When one lake filled up, its waters overflowed the banks and carved
the channels to a lower area where another lake would form. These dry lakes would
be targets to look for evidence (biosignatures) of past life.
On September 27, 2012, NASA scientists announced that the Curiosity rover
found direct evidence for an ancient streambed in Gale Crater, suggesting an ancient
“vigorous flow” of water on Mars. In particular, analysis of the now dry streambed
indicated that the water ran at 3.3 km/h (0.92 m/s), possibly at hip depth. Proof of
running water came in the form of rounded pebbles and gravel fragments that could
have only been weathered by strong liquid currents. Their shape and orientation
suggests long-distance transport from above the rim of the crater, where a channel
named Peace Vallis feeds into the alluvial fan.
8.3.3.2
Lake Deltas
Researchers have found a number of examples of deltas that formed in Martian
lakes. Finding deltas is a major sign that Mars once had a lot of liquid water. Deltas
usually require deep water over a long period of time to form. Also, the water level
needs to be stable to keep sediment from washing away. Deltas have been found
over a wide geographical range, though there is some indication that deltas may
be concentrated around the edges of the putative former northern ocean of Mars
(Fig.
8.5
).
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