There is no water left in it, but drill tests and a chemical analysis of its fine-grained rocks by the Curiosity robot's science instruments suggest microbial life could have thrived there billions of years ago.
The rocks contain signs of carbon, hydrogen, oxygen, nitrogen and sulphur, and "would provide perfect conditions for simple microbial life," said the report in the journal Science.
Small bacterial life forms known achemolithoautotrophs are known to thrive under similar conditions on Earth, and are typically found in caves and under the sea in hydrothermal vents.
"This is really similar to an Earth environment," said
While no life forms have been detected in the rocks, the mobile
"These are relatively young rocks in Martian history," Grotzinger told reporters, saying that among the "surprising results" of the latest findings was the rocks' age of 3.5 to 3.6 billion years old.
"That just happens to exactly coincide with the oldest records on Earth for which we have a microfossil record," he told a meeting of the
Water on the Mars
Researchers have already found evidence of water elsewhere on Mars' surface, and the work of past orbiters has strongly suggested Mars had lakes at some point.
The U.S. space agency chose the Gale Crater as the landing site for the unmanned, six-wheeled Curiosity rover -- which touched down in
The latest findings provide the "strongest evidence yet that Mars could have been habitable enough for life to take hold," said the study.
"This is the first time that we have actually found rocks on Mars that provide evidence of the existence of lakes," co-author
"This is great because lakes are a perfect environment for simple microbial life to develop and be preserved," he said.
The next step is to analyze specimens from a thick pile of rocks scattered on the crater's surface for further evidence of habitable environments, Gupta said.
Its mission is to search for geologic conditions that might have been right for life to exist, but it does not contain tools that can actually detect life.
Gupta said the latest findings are a "huge technical achievement," and that scientists have been surprised at the diversity of ancient environments they have found so far, from acidic and salty to gentler freshwater.
More unmanned rovers are scheduled to land on Mars in the coming years, including a European space agency robotic explorer called ExoMars in 2018 and another
"It gives us great confidence for the future and for this mission that we should carry on exploring," Gupta said.
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