NASA: Martians likely lived underground

If life ever existed on Mars, it's likely that its longest-lasting enclaves would be underground.

"If surface habitats were short-term, that doesn't mean we should be glum about prospects for life on Mars," says Bethany Ehlmann, the lead author of a new NASA report on the Red Planet, "but it says something about what type of environment we might want to look in."

The study, which examined different types of clays on the Martian surface, indicates that the most promising environments were likely subterranean – or, more probably, sub-Martian. "The most stable Mars habitats over long durations appear to have been in the subsurface," said Ehlmann in a statement announcing the findings.

"On Earth, underground geothermal environments have active ecosystems," she said, leaving open the possibility that such conditions may have existed – or may exist – on Mars.

The study was based on years of mapping Mars' surface minerals, conducted by both NASA and European satellites cruising around the planet, which examined more than 350 sites. From comparing the clays deposited at those sites by surface water, during a relatively brief period millions of years ago, with clays that were developed by subsurface waters, the researchers came to the conclusion that most of the action was underground.

"The types of clay minerals that formed in the shallow subsurface are all over Mars," said study co-author John Mustard. "The types that formed on the surface are found at very limited locations and are quite rare."