PARIS — Scientists have announced "the strongest evidence yet" of liquid water on Mars, raising the distant prospect of microscopic life on our neighbouring planet.
Curious lines running down steep slopes on the surface of the Red Planet may be streaks of super-salty brine, a team said on Monday.
Evidence of "hydrated" salt minerals in the streaks "strongly support the hypothesis" of liquid water on Mars – though not H2O as we know it, concluded a research paper in the journal Nature Geoscience.
If anything, it was likely "wet soil, not free water sitting on the surface," said study co-author Alfred McEwen from the University of Arizona.
NASA said the findings, made with its Mars Reconnaissance Orbiter, "provide the strongest evidence yet that liquid water flows intermittently on present-day Mars."
"Mars is not the dry, arid planet we thought of in the past," Jim Green, the American agency's planetary science director told journalists in Washington.
The presence of hydrated salt minerals in the lines, indicates that "water plays a vital role in the formation of these streaks," according to Lujendra Ojha of the Georgia Institute of Technology in Atlanta, who co-authored the study.
The minerals, called perchlorates, contain water molecules in their make-up.
It is widely accepted that the Red Planet once hosted plentiful water in liquid form, and still has water today, albeit frozen in ice underground.
Earlier this year, NASA said almost half of Mars' northern hemisphere had once been an ocean, reaching depths greater than 1.6 kilometres.
Anybody out there?
Astrobiologist Lewis Dartnell of the University of Leicester Space Research Centre said the study, which he did not take part in, presented "very strong evidence that what we believe to be signs of liquid water trickling down the Martian surface is in fact that."
This, in turn, raised the intriguing prospect of life, he said.
"If there is liquid water trickling beneath the surface, maybe that's an environment where bacteria and microbial life can survive... The results we've had this afternoon are very exciting because they increase the possibility that there is life alive on Mars today."
Others said it was early days yet.
"It's a smoking gun: Liquid water hasn't been seen directly in these 'dark stains'," said Mark McCaughrean, senior science advisor at the European Space Agency.
"Rather, they've spotted the kind of hydrated minerals that could make water briny enough to enable it to flow as a liquid at the extremely low, sub-zero temperatures on Mars. That makes the hypothesis that liquid water is involved in making those stains quite plausible, but isn't really a direct detection."
And even if briny water does exist: "whether or not that substantially improves the chances of us finding life on Mars... the jury is definitely still out on that," McCaughrean added. — AFP