The findings, published in Thursday's edition of the journal Science, are to be presented at the annual meeting of the American Association for the Advancement of Science in San Francisco.
 
Primitive life
 
Scientists have long debated whether water flowed on the red planet, with evidence increasing in recent years.
 
The presence of water would raise the possibility of at least primitive life forms existing there.
 
Okubo said minerals in the fluid strengthen and bleach the rock, making it more resistant to erosion than other areas.
 
Co-author Alfred S McEwen and Okubo said in the paper: "On Earth, bleaching of rock surrounding a fracture is a clear indication of chemical interactions between fluids circulating within the fracture and the host rock."
 
The researchers also said that layered outcrops can indicate cycles with materials deposited by regular episodes of water, wind or volcanic activity.
 
Craters revisited
 
Last December scientists reported evidence that water may be flowing through Mars' surface.
 
Images from the Mars global surveyor showed changes in craters that provided the strongest evidence yet that water moved through them recently and is perhaps doing so even now.
 
The surveyor had previously spotted tens of thousands of gullies that scientists believed were geologically young and carved by fast-moving water coursing down cliffs and steep crater walls.
 
Scientists decided to retake photos in a search for evidence of recent activity.
 
Two craters in the southern hemisphere that were originally photographed in 1999 and 2001 were examined again in 2004 and 2005.
 
The images showed changes which scientists say are consistent with water flowing down the crater walls.