It may be dry, but it once contained water. That’s the general consensus with the recent discovery. In a “striking upper part of the Reull Vallis region of Mars,” which reveal a 932-mile-long (1500 kilometer) river running from the Promethei Terra Highlands to the vast Hellas basin, once existed a riverbed that was 4.3 miles (7 kilometers) wide and 984 feet (300 meters) deep. It turns out that Mars very much was like our planet Earth (in this regard).
ESA Mars Express team says that the river was flowing with abundant water about 3.5 to 1.8 billion years ago, during the Hesperian period. After the Amazonian Era, the Reull Vallis was invaded by a glacier, which carved out the path. Some time after that, craters impacted the surface.
What can we take from this? There’s a lot more we have to examine about Mars. That is certain.