Claim: Candor Chasma is a  large canyon in the terrestrial planet Mars that contains branched channels that probably carried water, as Mars is said to have running water on its surface.
Evidence: The climate of Mars may have been such in the past that water ran on its surface. 
Liquid water on the surface of Mars cannot exist due to low atmospheric pressure, which is less than 1% of the atmospheric pressure on Earth, except at the lowest elevations for short periods. 
Liquid water cannot exist on the surface of Mars due to low atmospheric pressure, which is less than 1% that of Earth's, except at the lowest elevations for short periods.