Rovers and probes have provided some info on Martian soil and climate, but scientists want to bring a chunk of the Red Planet down to Earth on what's called a sample-return mission. Uh, remember The Andromeda Strain? What happens if some freaky virus comes back on NASA's planned 2018 sample return? WHY, GOD, WHY? Martian probes can't carry the full spectrum of scientific gear and monitors to the dirt, but they can bring the dirt back to instruments on Earth, buying time and flexibility for testing. And when it comes to Mars rocks, scientists love time and flexibility. Researchers spent more than a decade studying the Martian rock known as the Allen Hills meteorite (and found possible fossil evidence of life). If and when we bring back a coffee-cup-size sample from Mars in 2018, it will also need Earth-bound scrutiny. FEAR FACTOR NASA's Planetary Protection division ("Our mission is to prevent biological cross-contamination") plans to house everything in a special receiving facility on Earth similar to a level-4 biohazard-containment lab, the most secure kind. "The only thing that would be of concern is something that can replicate," says Margaret Race, a principal investigator with the Search for Extraterrestrial Intelligence (SETI) Institute who focuses on contaminants and planetary protection. "If it's radiation or toxins, we can deal with that." She believes the Mars sample could be just as vulnerable to Earthly microbes as people might be to any Martian germs. "We've gotten very good at biocontainment," Race says. "If something goes wrong, we could just autoclave"—sterilize—"everything." WORRY METER Low

Jon Proctor