To find life on Mars, scientists may need to give up surface exploration and "go deep."

Typically, Mars missions searching for signs of life target the planet's surface, at sites where there are signs of ancient water (a reliable indicator of where life is found on Earth). But while no life has turned up yet on Mars' surface, there may be an abundance of microbial Martians congregating underground, according to research presented Dec. 11 here at the annual meeting of the American Geophysical Union (AGU).

In recent decades, explorations underground on Earth have revealed the so-called deep biosphere — a subsurface environment teeming with microorganisms. And scientists suspect that a similarly biologically-rich zone may be thriving under Mars' surface, too. [Mars-like Places on Earth]

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