A NASA spacecraft orbiting Mars has discovered evidence of liquid water flowing through its soil, increasing the prospects for finding Martian life. Mars Reconnaissance Orbiter probe spotted seasonal changes in the landscape in warmer regions of the red planet at mid latitudes. 

Orbital imagery combined with 3-D modelling shows seasonal flows (NASA)

Dark, finger-like patterns recorded by its HiRISE camera on martian slopes are most likely to be caused by salty water, or brine, running within it. Expert geologists reckon that is the best explanation to fit the evidence they have collected, though they warn it is not conclusive proof.

The discovery, published in the leading journal Science, was heralded by a special press conference called by NASA tonight. One of the four scientists on the panel was Professor Lisa Pratt, of Indiana University, a leading expert in finding life deep underground on Earth and on Mars.

Her special interests are life in desert-like conditions, salty lakes, and evaluating how life might evolve on a planet like Mars with very limited water. Saltiness lowers the temperature at which water freezes. Sites with liquid brines could therefore be important to future studies of whether life exists on Mars.

As rumours of what NASA’s announcement might be, Professor Brian Cox, presenter of hit BBC shows Wonders of the Solar System and Wonders of the Universe, tweeted: “The context of a discovery of liquid water on Mars (if that’s what NASA have found) is that it greatly increases the prob. of finding life.”

The latest discovery comes two and a half years after NASA revealed they had observed plumes of methane on Mars, possibly produced by living martian organisms, though there are geological mechanisms too.

The new features are only about 18 inches to 5 yards wide but run for hundreds of yards along slopes. They are only seen on warmer slopes and are much narrower than gullies which are abundant on warmer or cold pole-facing slopes.

The MRO spacecraft detected hundreds of the streaks in some regions observed. They fade in winter but return in the next martian spring.

NASA scientist Alfred McEwen, who is in charge of the probe’s high-resolution HiRISE camera, said: “The best explanation we have for these observations so far is flow of briny water, although this study does not prove that.”

His Arizona University student Lujendra Ojha, who developed software that identified the markings, said: “I was baffled when I first saw those features in the images.

“We soon realized they were different from slope streaks that had been observed before. These are highly seasonal, and we observed some of them had grown by more than 200 meters in a matter of just two Earth months.”

Richard Zurek of NASA’s Jet Propulsion Laboratory, in California, said: “It’s hard to imagine they are formed by anything other than fluid seeping down slopes.”

NASA’s press conference tonight reported that flows had been identified at seven sites, with more candidates still to be identified. Around 1,000 flows had been spotted in Newton Crater alone.

The probe’s pictures showed the flows start to form in late spring and grow through the martian summer before they disappear. Sites where they are found are rare but they wee observed over three martian summers.

Life-on-Mars expert Professor Lisa Pratt said: “This is an eye-opening discovery that will really help us begin planning missions to look for signs of life on present-day Mars.

“I really think this is a very exciting discovery because it is our first chance to see an environment on Mars that might allow for the expression of an active biological process if there is present-day life on Mars.”

Head of NASA’s Mars program Mike Meyer said: “What we’ve found on Earth is that if there’s water there’s life. We have found repeated and predictable evidence suggesting water flowing on Mars.”

Leader of the discovery team Alfred McEwen said: “Where these dark flows terminate there are bright areas. This appears to be some deposit or residue left behind by these flows. The flows definitely repeat each year. These slopes are far too warm for carbon dioxide frost. We have circumstantial evidence for water.”

Geophysicist Philip Christensen of Arizona University said: “The mid-latitudes are turning out to be the place where a lot of the action is. They are turning out to be places where liquid water can actually exist.”

It is already known that vast quantities of water exists as ice on Mars. Droplets of water were thought to have been spotted on struts of NASA’s last Mars lander, Phoenix, before evaorating into space in the thin atmosphere.

Keen Mars-watchers will remember that NASA previously made claims for signs of running water on Mars but backtracked soon afterwards when it was shown that they were probably just landslides of debris. This time the evidence seems a lot more compelling!