[meteorite-list] Digging for Life in the Deadest Desert

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu Aug 5 12:30:49 2004
Message-ID: <200408051630.JAA13246_at_zagami.jpl.nasa.gov>

http://www.cnn.com/2004/TECH/space/08/04/atacama.desert/
  
Digging for life in the deadest desert

Driest spot on Earth may hold clues to Mars

By Michael Coren
CNN
August 5, 2004

(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 Endurance, 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.

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."

"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 technology could be ready for the Mars
Science Laboratory rover set to launch for Mars around the end of this
decade.

CNN's Miles O'Brien contributed to this report.
Received on Thu 05 Aug 2004 12:30:42 PM PDT