NASA's steady reconnaissance of Mars with the Curiosity rover has produced another major discovery: evidence of an ancient lake with water so low in salinity and so neutral in acidity that it could plausibly be described as drinkable.
Scientists have known that the young Mars was warmer and wetter, but this is the best evidence yet that the planet had what people would call swimming holes (though scientists say you'd have wanted to wear a wet suit).
The "fresh water" lake could have harbored life, in theory. The chemistry of the lake would have been congenial to organisms known as chemolithoautotrophs — mineral-eaters. Whether such organisms, which thrive on Earth in exotic environments such as caves and deep-sea hydrothermal vents, existed on the young Mars is a question Curiosity lacks the tools to answer.
The findings were published online by the journal Science and will be discussed in San Francisco at the annual meeting of the American Geophysical Union. Scientists had announced this year that they'd found signs of an ancient lake within Gale Crater, but the new reports provide a much more detailed analysis. The lake existed 3.6 billion years ago and stuck around for thousands of years, at least, the new reports conclude. Previous discoveries suggested that Mars once had surface and groundwater with the quality of battery acid, but the water in this lake looks much more benign.
"If we put microbes from Earth and put them in this lake on Mars, would they survive? Would they survive and thrive? And the answer is yes," said John Grotzinger, a Caltech planetary geologist who is the chief scientist of the Curiosity rover mission. He is the lead author of a paper titled "A Habitable Fluvio-Lacustrine Environment at Yellowknife Bay, Gale Crater, Mars."
"In March, we did know that we had a lake, but what we weren't sure of was how big it was and how long it lasted, and also we were not sure about the broader geological context that supports the presence of lakes coming and going for a very long time," Grotzinger said.
"I'm most excited about the nature of the water," said Jim Bell, an Arizona State University scientist who has worked with the cameras on Curiosity as well as two precursors, Spirit and Opportunity. "What we're seeing in Gale Crater is evidence of fresh water. Very neutral. Drinkable."
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