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. ... 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. ...
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. ...
"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. ... On Mars, it [bio-viability -- EBB] 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." ...
"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. ...
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."
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. ... 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.
A little Andromeda strain action, anyone?
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.