Scientists following the NASA Mars rover believe they have found evidence of gravel once carried by a fast-moving ancient stream.
The roving laboratory, Curiosity, is on a two-year mission to determine whether Mars was ever able to support microbial life.
Proof of water once having been on the Red Planet has been found in the past, but this is the first time stream bed gravel has been documented.
Analysis of a slab of rock located between the crater's north rim and the base of Mount Sharp indicate a fast-moving stream of water once flowed there.
Images released on Thursday show rounded stones cemented into rock.
The rocky outcrop, called "Hottah," looks "like someone jack-hammered up a slab of city sidewalk, but it's really a tilted block of an ancient stream bed," project scientist John Grotzinger said.
The stones inside the rock are too big to have been moved by wind, Curiosity scientist Rebecca Williams, with the Planetary Science Institute in Tucson, Arizona, said.
"The consensus of the science team is that these are water-transported gravel in a vigorous stream," Williams said.
Life on Mars?
The finding, however, does not necessarily point to life on Mars. While water could support life, it isn't proof of former life on Mars.
"The question about habitability goes beyond the simple observation of water on Mars," said lead scientist John Grotzinger at the California Institute of Technology.
"Certainly flowing water is a place where microorganisms could have lived. This particular kind of rock may or may not be a good place to preserve those components that we associate with a habitable environment," he said.
Scientists have not yet decided whether to chemically analyze the slab of rock or wait and look for better targets in which to look for evidence of life.
The $2.5 billion Mars Science Laboratory Curiosity mission is NASA's first astrobiology mission since the 1970s-era Viking probes.
tm/av (AFP, dpa, Reuters)