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Universe teeming with elements of life

The Washington Post: Astrobiologists say the building blocks of life pervade the solar system, and probably the universe. But what about life itself?
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The building blocks of life pervade the solar system, and probably the universe, locked up in planetary polar ice caps, crouching in the interstices of ancient volcanic rocks, zooming around on comets and meteorites, drifting between galaxies in interstellar space, or wafting gently down in cosmic dust.

"The universe is hard-wired to form a lot of the compounds that make life," says astrophysicist Scott A. Sandford of NASA's Ames Research Center. "But that doesn't mean it's happening. There may be a lot of places where the process gets frustrated, and since we haven't seen it on any planet except our own, it's just a story."

But it is a story that scientists take ever more seriously. This year, especially, the study of possible life forms elsewhere in the universe has taken on a new shine, brightened by the spectacular success of the Mars rovers Spirit and Opportunity in discovering the first physical evidence that liquid water once rested on the surface of a celestial body other than Earth. Water, a fundamental requirement for life as scientists can imagine it, is known to be ubiquitous in the universe, but actually finding physical evidence of its past presence on Mars has nevertheless had a galvanizing effect.

Last week, 700 scientists and engineers showed up for the Astrobiology Science Conference 2004 at the Ames center, bringing together researchers whose interests ranged from building DNA in the lab to listening for radio signals from intelligent beings far, far away.

"People take different paths," said astrophysicist Mario Livio of NASA's Space Telescope Science Institute in Baltimore. "A lot of people look at Earth and draw analogies. Astronomers look at the solar system, meteorites and comets, or they look for extrasolar planets" orbiting distant stars.

The Mars rovers have offered scientists a chance to move from speculation to more practical questions: If there is life elsewhere, what form will it take? What should we look for?

"It will be microbial," said University of Colorado molecular biologist Norman Pace. "It will be a bunch of different microbes in a community-based environment. The rules of the game will be different, but there will be a suite of organisms designed to cope with their geophysical situation."

Depending on the scientist, however, there were varying views about even such basic questions as when something becomes "life." Livio described "a simple something able to replicate and pass on information." Sandford said he would look for "an accumulation of functionalities" — the organism would "know its inside from its outside" and be able to "drag electrons around" to form different compounds.

A no-brainer for researchers
But regardless of the definition, the rationale behind the search for microbes on Mars or elsewhere in the solar system appeared to be a no-brainer among the researchers: "More than 85 percent of the history of life on Earth is exclusively the history of single-celled organisms," said Ames research scientist David Des Marais, a member of the Mars rover team. "On Earth microbial life runs the place. It's going to be the easiest to find."

Also, noted Ames astrobiologist Jonathan Trent, microbes have demonstrated remarkable ability to endure in hostile environments. "We find them in near-boiling sulfuric acid, in ice, growing in high levels of radiation," he said. "If you find me a microbial life form somewhere else in the solar system, I think it will be very similar to what we have here. To look for anything else in our solar system is absurd. Beyond our solar system, of course, all bets are off."

To exist and prosper, microbes (the generic term for microscopic organisms) have a couple of chemical requirements, chief among them liquid water. "There might be another solvent," Sandford said. "But water is one of the most abundant substances in the universe," and it also has the priceless ability to act as a medium for the formation of the complex, yet stable, carbon-based organic molecules that make up living organisms. Scientists say there is little doubt that carbon, which on Earth is contained in more compounds than all other elements combined, will serve as the raw material for life forms on other worlds.

"Carbon can form multiple chemical bonds, and fold and bend in the presence of water," Sandford explained. "There's nothing like it."

And like water, carbon is everywhere. Mars's atmosphere is composed mostly of carbon dioxide, and its polar caps contain dry ice as well as water ice. Comets spew carbon compounds such as methane, methanol, ethane and formaldehyde from their tails, and planets like the "gas giants" Jupiter, Saturn, Uranus and Neptune are cloaked in gaseous hydrocarbons, too.

But did organisms arise?
Having conditions necessary for life does not, however, mean that life has to happen. Cornell University's Stephen W. Squyres, lead scientist for the Mars rovers team, acknowledged in a conference lecture that Opportunity's discovery of what may have been a salt sea on the Martian surface was evidence "of what was once a habitable environment," but he took care in subsequent remarks to note that "I have no idea" whether organisms ever lived there.

And besides the necessary chemicals, there are a host of other circumstances that may have to align perfectly before life can develop. Many of the extrasolar planets so far discovered have elliptical orbits, so they travel both too far from and too close to their stars. Venus, almost the same size as Earth, has a circular orbit, but is 26 million miles closer to the sun. Is it too hot for life to form?

Livio noted that the moon stabilizes the Earth's axis, preventing wobbling that could perhaps cause catastrophic climate change. And, he asked, what effect could the bombardment of other planets by asteroids or comets have in causing mass extinctions like those that occurred on Earth? Or how important is it for a planet like Earth to have a molten iron core to create a magnetic field that fends off potentially lethal radiation?

"You have to remember that we only have one case so far," Sandford said. "In a situation like that, anything we take as a starting point has the possibility of being fundamentally flawed."

Life on Mars? Stay tuned
As far as life on Mars, proof -- if it is there -- will probably have to wait for the next trip, scheduled for 2009. Spirit and Opportunity were designed to search for water, and in coming weeks and months they may gather new information to enable scientists to make better guesses about the extent of water on the Martian surface, and how long it was there. But the rovers are not equipped to identify the presence of organic compounds, and so will leave scientists tantalized but unsatisfied.

Of particular interest are the so-called blueberries, tiny spherical grains that contain significant amounts of iron oxide likely to have been formed as minerals that crystallized in water around a central core, then dropped out of the parent rock when it eroded. Opportunity has found blueberries everywhere as it explores Mars's Meridiani Planum.

"The blueberries are more than a third or even more than half hematite [an iron oxide], but there's also a component we haven't identified," said Ames's Des Marais. On Earth, such pebbles often conceal the fossil remains of microorganisms. Des Marais acknowledged that "that's on the list of possibilities," but it appeared certain that the origin of the blueberries will not be resolved during the current mission. But he agreed with Squyres that Meridiani Planum would be a great place to come back to.