Two years ago, NASA made the announcement that the surface of Mars featured running water systems. This observation was based on the appearance of seasonal flows, called “recurrent slope lineae,” or RSL.
A study appears to have disputed that claim.
The authors wrote: “Flowing liquid water in the current Martian climate has always been an extraordinary claim. The observations and interpretations presented here suggest that RSL are no longer extraordinary evidence,” according to the study published in Nature Geoscience (pdf).