Two NASA rovers are about 5,200 miles apart on the surface of Mars and will likely never meet.

But though they roam alone, Curiosity and Opportunity continue to reveal details about the Red Planet's former habitable conditions. New studies in the journal Science describe insights from each of those rovers about ancient environments where microorganisms could have once lived.

"These results demonstrate that early Mars was habitable, but this does not mean that Mars was inhabited," writes John Grotzinger, lead scientist on the Curiosity mission, in an introduction to the studies in the journal Science.

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