A new study of photographs taken from orbit suggest water flowed on Mars as recently as a few years ago, raising the possibility the planet could support life.

The images, taken from aboard a satellite, don't show water, however. Instead, they show recent changes in surface features that might have been made from the flow of liquid water.

This satellite file photo shows gullies on the walls of a meteor crater in the Newton Basin on Mars. Photos of other gullies on the planet suggest water may have flowed through them in the past decade.
(NASA, Jet Propulsion Laboratories/Associated Press)

What distinguishes the latest findings is the suggestion that liquid water moved through the Red Planet not eons ago, but in the last 10 years.

If the evidence proves accurate, it would be a major find for researchers of the dry and cold planet. Water is known to exist as ice on the planet's north pole, but liquid water has only been theorized to have existed.

NASA will be holding a press conference on Wednesday to discuss the new findings, which will also be published in the journal Science.

"This underscores the importance of searching for life on Mars, either present or past," said Bruce Jakosky, an astrobiologist at the University of Colorado at Boulder, who had no role in the study. "It's one more reason to think that life could be there."

The photos were taken in 1999 by the Mars Global Surveyor, the orbiting satellite NASA abruptly lost contact with last month and have failed to locate.

Bright, light-coloured deposits discovered

The surveyor took photos of gullies and trenches scientists believed were geologically young and carved by fast-moving water. Scientists at Malin Space Science Systems who operated a camera aboard the spacecraft decided to re-take the photos to see if any recent changes had occured on the surface. The photos were then re-imaged in 2004 and 2005.

The scientists found bright, light-coloured deposits in the gullies not present in the original photos. They concluded the deposits — possibly mud, salt or frost — were left behind when water recently travelled through the channels.

Oded Harrison, an assistant professor of planetary science at the California Institute of Technology, said although the interpretation of recent water activity on Mars was "compelling," the deposits could also have been moved by the flow of dust.

The subzero surface temperatures and low atmospheric pressure of Mars preclude water from remaining a liquid for long. Once it reaches the surface, it would either freeze into ice or disperse in the atmosphere as gas.

But some studies have suggested the possibility that liquid water could be briefly appearing on the surface from an underground water source. If there was such a source, it would suggest both water and a stable heat source, two key conditions for supporting an environment favourable to life.

The Mars Reconnaissance Orbiter, launched in 2005, is also testing the Martian atmosphere and surface and will search for evidence of water, past and present, just below the surface. Its observations will be complete in December 2008.

With files from the Associated Press