NASA has compelling evidence of seasonal salty water flows on Mars, an important finding that substantially raises the prospect that life, in some form, exists today beneath the planet's desiccated red surface.

The discovery, announced early on Tuesday morning, Australian time, by the US space agency, is based on a series of unusual surface streaks that seem to change with the vagaries of the Martian seasons.

The streaks, which appear on slopes during warm seasons, lengthen and then fade during cooler seasons, were recorded by NASA's Mars Reconnaissance Orbiter.

"This is a very important finding, which really increases the likelihood of habitable micro-environments existing on Mars," says Mars Society president Dr Jon Clarke.

On Earth water is an essential ingredient for biological organisms and, if life does exist on Mars, it is most likely to be found in association with liquid water.

Confirmed evidence of even seasonal running water on the surface would demonstrate there are local aquifers or some other kind of water table source where life could shelter, protected from the harsh radiation and low temperatures of the fourth planet from the sun.

Scientists previously thought that there was no direct evidence for liquid water near the surface to flow out and that, if it did ever breach the surface, it was too cold and the atmosphere too thin for it to persist long enough to flow: the water would rapidly either instantly freeze or sublimate.

"The key finding by NASA is that any observed running water probably contains dissolved salts, which lower its freezing temperature, thus allowing it to remain liquid on the surface long enough to flow," says Mars Society director Guy Murphy.

As hardy microbes on Earth, called halophiles, thrive in conditions of extreme salinity, scientists are not ruling out the idea that unusual microbes survive under the harsh Martian conditions.

"This is the first time we've confirmed flowing water outside of Earth," says Swinburne University astrophysicist Alan Duffy. "The find supports our search for life on Mars as, to put it simply, where there's water there's life."

Mars watchers believe that, during the summer months, ice beneath the planet's surface dust is melted and rises as a brine that then flows down slopes.

"The entire flow might only be a few centimetres deep – but this would darken the soil enough for instruments to observe this from space," Dr Duffy says.

Unfortunately, there's no craft nearby that can test the soils. "So, proving that life is there is going to take longer," Dr Duffy notes. "But if NASA really has found flowing water, then at least we know where to search for life – whatever shape it might take."

Note: The Ridley Scott movie, The Martian, starring Matt Damon as the astronaut left behind on the red planet after a fierce dust storm, screens in Australia on Thursday. One of the most scientifically accurate movies ever made about Mars, it was produced in consultation with NASA scientists.

Please send bright ideas for new topics to Fairfax science columnist Peter Spinks at pspinks@fairfaxmedia.com.au