Via Steve Spaleta at LiveScience:
Mawrth Vallis – The outflow channel is ~373 miles long (600 km) and about 1.2 miles deep 2 km). The indicators of liquid water in the past have made this area a landing site candidate for the ExoMars 2020 mission. More.
See also: Huge ice lake under surface of Mars?
Researchers: Life could only exist on Mars far beneath surface
and
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