A US space agency rover roaming the dry surface of Mars has for the first time uncovered direct evidence of what used to be a freshwater lake.
Drill tests and chemical analysis of fine-grained rocks by the Curiosity robot’s science tools suggest conditions were right for the lake to have once supported microbial life, perhaps 3.6 billion years ago.
The rocks contained signs of carbon, hydrogen, oxygen, nitrogen and sulphur, and “would provide perfect conditions for simple microbial life”, said the report in the journal Science.
Bacterial life forms known as chemolithoautotrophs are known to thrive under similar conditions on Earth, and are typically found in caves and under the sea in hydrothermal vents.
The findings were described at a meeting of the American Geophysical Union in San Francisco, California.
“This is the first time that we have actually found rocks on Mars that provide evidence of the existence of lakes,” co-author Sanjeev Gupta of Imperial College London told AFP.
“This is great because lakes are a perfect environment for simple microbial life to develop and be preserved,” he said.
Gupta said the mobile Mars Science Laboratory has drilled into the mudstone and sandstone rocks and found clay minerals, suggesting an interaction with water.
The sandstone also resembles that found in Earth rivers, leading scientists to hypothesise that a river once flowed into the lake.
The US space agency chose the Gale Crater as the landing site for the six-wheeled Curiosity rover – which landed in August 2012 – specifically because it was believed to contain many geological layers and likely held water.
The latest findings provide “the strongest evidence yet that Mars could have been habitable enough for life to take hold”, the study said.
The $2.5 billion car-sized rover is operated by NASA engineers at the Jet Propulsion Laboratory in Pasadena, California.
Its mission is to search for geologic conditions that might have supported life, but it does not contain tools that can detect life.