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Science & Space

Digging for life in the deadest desert

Driest spot on Earth may hold clues to Mars

By Michael Coren
CNN

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Long ago, this core region of the Atacama mysteriously dried and then died out (above). Scientists say something similar happened on Mars (below).
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(CNN) -- Life is hard. For some, it's almost impossible.

Specialized microorganisms called extremophiles thrive in nuclear waste, volcanic vents, boiling geothermal geysers and even deep inside rocks. Their unique biology allows them to feast on chemicals and radiation that would kill most organisms.

But there is a place on Earth so hostile to life that even extremophiles perish: Chile's Atacama Desert.

"Here is the only place where we've really crossed a threshold where we find no life," says Chris McKay a NASA geologist studying the Atacama.

"You go to the Antarctic, the Arctic, any other deserts we've been, scoop up dirt and you find bacteria. This is the only place that you would find nothing."

The rocky desert on a high plateau along South America's Andes mountain range appears lifeless.

Scientists have been unable to find plants or cells living in many parts of the desert. Even bacteria do not last long in the barren, acidic soil.

The reason, at least in part, is that the Atacama Desert lacks water. It is the driest place on Earth. Rainfall is measured in millimeters per decade, and some areas have not seen precipitation in hundreds of years, scientists say.

At its arid core, the Atacama -- about two-thirds the size of Italy -- is the closest thing to Mars on our planet.

That characteristic is attracting a horde of at least one unique life form: NASA scientists.

"This is a very good place to be testing exploration strategies for Mars," says Nathalie Cabrol, a planetary geologist with NASA and the SETI Institute which searches for extraterrestrial life.

The space agency is examining how moisture levels in the desert define where life exists and where it dies out.

By understanding the absolute limits of life on Earth, scientists hope their search for life on other planets such as Mars will be more likely to succeed.

"Where does life check out and say, 'This is too much for us,'" says McKay. "We can by driving across this desert take a trip in time on Mars. ... And we can chart where that transition occurred and then we can apply it to Mars."

A habitable Mars

When the solar system was younger, the conditions on Mars were more like those on Earth today.

"[Ancient Mars] is equivalent to what we find in the Andes at 20,000 feet," said Cabrol. "It's totally equivalent to life on Mars 3.5 billion years [ago]."

Discoveries made by the Mars rovers, Spirit and Opportunity, are confirming these theories. Their observations suggest Mars was once a much wetter planet with an atmosphere, salty seas and flowing streams.

New evidence across Mars is popping up from ancient deltas and gullies that crisscross the planet to fossilized ripples of waves frozen in stone.

But there is a crucial difference.

The evolution of life on Mars would have been totally different from that on Earth, where a "habitable" zone has existed for 4.5 billion years, says Cabrol.

On Mars, it lasted perhaps 1 billion years before reappearing only episodically. Also, the substance essential to life as we know it -- water -- is even less abundant on Mars than in the Atacama desert.

As a result, any life would probably have to hunker down away from the radiation and aridity.

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Scientists are probing the Atacama Desert trying to understand why there is nothing living in the dirt.

But scientists say if the three ingredients for life exist together on Mars -- energy, nutrients and water -- then life can exist too. But it won't be easy to find.

"It's probably hiding from surface conditions," says Cabrol. "We'll have to be even smarter on Mars than in the Atacama."

Researchers hope the Atacama will refine the techniques to detect extraterrestrial life. Assays to identify chemical signatures of life are becoming ever more sensitive to find the hardiest biological specimens.

"What we are looking for is the toughest form of life on Earth: spores," says Adrian Ponce, a scientist at the Jet Propulsion Laboratory in Pasadena, California.

Spores, the dormant form of some species of bacteria, exist to survive hard times. This type of hibernation shields microorganisms from the effects of dehydration, radiation and lack of nutrients.

It also makes them superb astronauts. Spores are so resilient, they have survived direct exposure to space with virtually no protection.

The Long Duration Exposure Facility, deployed in orbit in 1984, carried microorganisms among its array of experiments. It remained in orbit longer then expected until it was finally retrieved in 1990 about six years later.

NASA scientists found that the bacterial spores had lain dormant on the facility. Except for those directly exposed to solar radiation, the spores showed few problems reviving after their six-year voyage.

Scientists were "impressed," said Michael Meyers, NASA's senior scientist for astrobiology.

"Spores are pretty good at survival," he said. "It's a combination of drying out and reducing the number of mutations caused by radiation. They have fairly robust repair mechanisms."

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"It's sort of a crime scene investigation. There was life here. ... We've got to pull that out," says NASA geologist Chris McKay.

That evidence adds credence to a theory called panspermia, which suggests life could hitch a ride inside meteors and comets and move between planets relatively insulated from space.

"I think its reasonable that you can have panspermia in the solar system," said Meyers.

He added that interstellar travel -- between solar systems -- was far less likely.

"Getting hit by cosmic radiation pretty much wipes you out," he said.

NASA has taken the theory seriously enough to establish a Planetary Protection Office. The official in charge, our Planetary Protection Officer, ensures spacecraft are clean of biological organisms and protects the Earth from lifeforms retrieved in samples from space and other planets.

That's one reason scientists are trying to boost the sensitivity of their instruments. The last such experiment, the Mars Viking probe, failed to detect life on Mars. Yet if Viking had landed in the Atacama Desert on Earth, it would also have concluded that Earth was a dead and desiccated planet.

Ponce is committed to making sure that mistake is not made if life exists on Mars.

"If there is a single spore, we want to be able to detect it," he says.

At the moment, the instrument he has designed is a table-top device that must be miniaturized and refined before it is ready to fly. It won't arrive on Mars any time soon.

If the hardware passes a field test in the Atacama Desert this year and funding follows, Ponce says the technoloy could be ready to fly next decade after the Mars Science Laboratory arrives on the Red Planet in 2010.

CNN's Miles O'Brien contributed to this report.


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