Recent studies indicate that water may have flowed in such places within the past five years, bringing new bacterial cells from deep underground.
(Related news: "Mars Has Liquid Water, New Photos Suggest" [December 6, 2006].)
Of particular interest is the Elysium Basin, a region on Mars where ice may remain from a sea's worth of water disgorged onto the surface five million years ago.
There, Dartnell's team calculated, dormant bacteria might still survive 25 feet (7.5 meters) deep in the ice, waiting to be thawed out and coaxed back to life.
Being able to drill deep enough to find live bacteria would be the "holy grail for astrobiologists," Dartnell noted.
Gregory Delory, a physicist from the University of California, Berkley, has studied toxic chemicals in the Martian soil and their potential impact on finding life.
Finding live bacteria "is a subject that colleagues and I have discussed for quite some time," Delory said via email.
Just because Earth-based life would have a hard time withstanding radiation on the red planet, he noted, that doesn't mean life born on Mars might not have found a way to survive.
"In the end we're stuck with the same question, whether it is peroxides, radiation, ultraviolet [light], toxic dust, a thin atmosphere, freezing, large temperature swings, etc.," he said.
All of these things are bad for life, but only for life as we know it.
"So the question remains Does life adapt to its environment, or is there only a narrow range of environments where life can survive?" Delory said.
"The answer is the same—we need to explore Mars in much more detail to find out."
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