Catching a free ride to Mars takes more than sticking out a thumb, but some hardy Earth bacteria could survive as hitchhikers clinging to the outside of spacecraft, studies have shown.

Now a set of experiments going up with space shuttle Atlantis to the International Space Station will test how exposure to the harshness of space might change bacteria during a simulated Mars mission.

"We are interested in understanding what types of damage are induced in cells and their DNA by exposure to space, what types of mutations may be induced, and how these mutations might drive evolutionary adaptation to the extreme selective environment of Mars," said Wayne Nicholson, a University of Florida Institute of Food and Agricultural Sciences astrobiologist working from NASA's Space Life Sciences Laboratory at the Kennedy Space Center.

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Although previous tests exposed different microbes to the space environment for up to six years, Nicholson noted that the experiments mostly "tested whether the bugs could survive long-term exposure to space" as opposed to seeing how the bacteria changed in response to space radiation.

Bacteria that can survive extreme environments interest researchers for several reasons.

Any Earth bacteria that escaped NASA's "clean rooms" and took a trip to Mars might contaminate efforts to find evidence of Martian life.

Looking beyond that, bacteria that can survive long space journeys on comets or interplanetary shards also provide evidence supporting the panspermia theory that the seeds of life are everywhere and can survive hopscotch trips from one space object to the next.

The current shuttle experiment — a collaborative effort between the University of Florida, NASA, the European Space Agency and the German Aerospace Center (DLR) in Cologne — will take place for more than a year on an external space station platform called EXPOSE.

That platform will be installed outside of ESA's Columbus laboratory module upon delivery by space shuttle Atlantis flight STS-122.

"Our immediate goals right now are to hope for a safe launch and deployment, and to work on our simulations and ground control experiments so that we will be completely prepared for processing the samples when they return from Earth orbit," Nicholson said.

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