The discovery is based on a detailed study of the dried-up river deltas and thousands of river valleys that scatter the Martian surface.
The MRO, for instance, will look for the trace signatures of minerals that form in the presence of water by scanning and mapping the Martian surface with advanced visible and infrared spectrometers.
Rover operators on Earth drove Opportunity cautiously and made several stops along the way to check out interesting Martian surface features.
