Portions of the Martian surface shot by NASA's Mars Reconnaissance Orbiter show many channels from 1 meter to 10 meters wide on a scarp in the Hellas impact basin, in this photograph taken January 14, 2011 and released by NASA March 9, 2011.[Photo/Agencies]

The discovery "confirms that water is playing a role in these features," said planetary scientist Alfred McEwen, with the University of Arizona. "We don't know that it's coming from the subsurface. It could come from the atmosphere."

Whatever the water's source, the prospect of liquid water, even seasonally, raises the intriguing prospect that Mars, which is presumed to be a cold and dead planet, could support life today.

However, McEwen said much more information about the water's chemistry would be needed before scientists could make that assessment.

"It's not necessarily habitable just because it's water - at least to terrestrial organisms," he said.

The evidence that there was water on the planet recently was the key finding in the study released on Monday. NASA's ongoing Mars rover Curiosity has already found evidence that Mars had all the ingredients and suitable habitats for microbial life to exist at some point in its past.

Scientists have been trying to figure out how it transformed from a warm, wet and likely Earth-like planet early in its history into the cold, dry desert that exists today.

Billions of years ago, Mars, which lacks a protective, global magnetic field, lost much of its atmosphere. Several initiatives are under way to determine how much of the planet's water was stripped away and how much remains locked in ice in underground reservoirs.