The Spirit & Opportunity rovers found evidence that water once flowed on this planet
[DOC] [TLE] Martian gully theory doesn't hold water, study finds - LA Times [PAR] Jul 29, 2016 ... Gullies on Mars were not carved by water, but were probably ... gullies on the 
Red Planet may not have been formed by liquid water, ... For example, NASA's 
2004 rovers Spirit and Opportunity, as well as ...