On the final frontier, pollution from Earth?

When NASA's current pair of Mars rovers, Opportunity and Spirit, open their airbags and bounce onto the surface of Mars next January, chances are they will be carrying more than just equipment.

As they prowl the dusty surface, scratching rocks and searching for evidence of life on the red planet, the twin rovers may themselves be carrying life from our green and blue planet. Nooks and crannies on space equipment can harbor Earth microbes and some may be capable of surviving a trip in space.

Scientists don't know if exotic Earth microbes can take root in the Martian environment. Compared to Earth, Mars is frigid and bathed in ultraviolet radiation strong enough to kill most known life-forms. Yet some worry Earth's microbes could survive there, perhaps sheltering under the soil or getting into underground Martian water. If we were to contaminate a pristine planetary ecosystem, they say, the implications would be huge.

"We know if you move organisms from one place to another on Earth you can cause ecological disruption," says Margaret Race, a consultant ecologist who specializes in the field of space contamination. "So when we go to Mars we have to do our science responsibly."

The concerns are heightened, Dr. Race says, because the rovers are going to Mars specifically to look for signs of Martian life. Scientists don't know if it's there or it's alive, she says. It could be merely remnants mixed with the Martian soil. "In order to look for those," she adds, "you don't want to add on a lot of other materials like contaminants from Earth."

But preventing biological contamination of space equipment is difficult. Every surface of every object on Earth is crawling with a microbial film. Scientists have found microbes living miles down in the Earth's crust. They are in hot volcanic vents in the ocean, in sea ice, and in the radioactive cores of nuclear-power plants. And recent research shows they can survive in a patch of the Canadian Arctic that resembles the Martian landscape.

The Sisyphean task of keeping those bugs off NASA spacecraft destined for Mars takes place at the Jet Propulsion Laboratory in Pasadena. Since sensitive space equipment can be easily damaged by heat, technicians can't boil or steam clean. In clean rooms, with hairnets and robes, they swab spacecraft parts with hydrogen peroxide and use ultrasound to shake microbes loose, employing the same technology used in the ultrasonic toothbrush.

NASA says it's not taking any chances. "The number of microbes you'll find attached to a spacecraft is fewer than you'd find in half a bottle of spring water," says John Rummel, NASA's planetary protection officer. That sounds reassuring, except that it means there could be as many as 300,000 microbial spores per spacecraft. NASA hasn't yet sent up a completely sterile spacecraft and Dr. Rummel says the agency doesn't plan to absolutely sterilize its equipment until there is a strong chance of a mission encountering actual water or ice.

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