Mars Life May Be Too Deep to Find, Experts Conclude
Richard A. Lovett
for National Geographic News
|February 2, 2007|
If life exists on Mars, it won't be found close enough to the surface to be easily discovered by robotic probes, a team of European scientists has concluded.
That's because any bacteria that may once have lived on the surface have long since been exterminated by cosmic radiation sleeting through the thin Martian atmosphere.
Billions of years ago the red planet may have been remarkably Earthlike, said astrobiologist Lewis Dartnell, author of Life in the Universe: A Beginner's Guide and a graduate student at University College London.
Then the Martian climate collapsed, producing the cold, dry world we see today (images of Mars).
If Earthlike life survived the climate shift, it would most likely be bacteria that live close to the surface.
Such bacteria would spend most of their time dormant, waiting for rare geological events to bring water from deeper in the planet.
Unfortunately, Dartnell said, such a scenario would have left the bacteria vulnerable to years of radiation damage.
In a study published January 30 in the journal Geophysical Research Letters, Dartnell's team found that even the most radiation-tolerant Earthly bacteria would survive only 18,000 years at the surface.
Bacteria living at greater depths could survive longer.
But even at 6.5 feet (2 meters)—the greatest depth at which a Mars probe scheduled for launch in 2013 will be capable of reaching—survival time would be 90,000 to half a million years, depending on the type of rock.
The best places to look, the team concluded, are frozen crater lakes or gullies in the sides of craters.
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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