By Tina Hesman Saey

Web edition: October 19, 2012
Print edition: November 3, 2012; Vol.182 #9 (p. 32)

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To make sure microbes from Earth don’t tag along on interplanetary trips, the Mars-bound Curiosity rover was assembled in a clean room.

Credit: NASA

Catharine “Cassie” Conley has the coolest job title at NASA: She’s the agency’s planetary protection officer. (The best title used to be “director of the universe,” but a reconfiguration a few years back eliminated that job description, she says.)

Since 2006, Conley (right) has been charged with preventing Earth from being overrun by extraterrestrial microbes or other contaminants brought back by NASA explorers. She also makes sure spacecraft don’t carry stowaways that could spread to other planets or later be mistaken for E.T. “I’m a policeman, basically,” she says.

Only one other person in the world — her counterpart at the European Space Agency — has full-time responsibility for guarding planets, moons and other celestial bodies from contamination. “It’s unfortunately a very small police force,” Conley says.

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Catharine “Cassie” Conley is NASA’s planetary protection officer.

Credit: NASA

But it’s a job she was practically born to do. Conley’s father was a mathematician who consulted with NASA to plot the trajectory of the Apollo missions to the moon. Her mother was a geneticist. “In kindergarten when they asked me what I wanted to be when I grew up, I said, ‘genetic engineer,’” she remembers.

Eventually she became a cell biologist, but one with more broad-ranging credentials than usual. In college, Conley realized that space exploration is an international endeavor and added a major in language translation (Russian and French) to her science courses. Her combined background has helped prepare her to deal with international bureaucracy and to understand both the engineering challenges of missions and the biology of organisms she’s trying to keep from colonizing other planets.

Before her current job, Conley worked at NASA’s Ames Research Center in California. She and her colleagues sent tiny, transparent nematode worms into orbit aboard the space shuttle Columbia on its last mission in 2003. Surprisingly, the worms survived when the shuttle disintegrated and burned up on reentry, teaching Conley and NASA just how resilient life can be and reinforcing the need for planetary protection.

Keeping spacecraft from contaminating other planets not only ensures that Earth organisms aren’t later mistaken for Martian life, it’s also necessary to make sure that Earthlings — big or microscopic — don’t become invasive or spread disease across the solar system, Conley says. She takes an object lesson from the European colonization of the New World, in which native populations were decimated by diseases carried by explorers. “That is exactly what we’d like to avoid,” she says.

Keeping Mars clean
A planetary protection officer’s job is to make sure that other planets don’t become contaminated with Earth life. Spacecraft sent to areas where life-supporting ice or water could be found must meet the strictest standards. Here are a few examples of how NASA has protected Mars.

• Viking landers The 1976 mission’s two craft were scrubbed and then baked. Even so, as many as 30 live organisms may have survived in the spacecraft, NASA estimates.
• Spirit and Opportunity Airbags used during landing were heat-treated to kill spores, and air filters and alcohol wipes helped make sure other parts didn’t carry too many bacterial spores to Mars. 
• Phoenix The spacecraft landed near Mars’ north pole in May 2008. Most of the lander was scrubbed clean, and the arm used to dig into ice caps was also baked.
• CuriosityThe new rover is the cleanest craft sent to Mars since Viking. It was scrubbed so that it had fewer microbes on its whole surface — an area roughly equal to a football field — than are typically found on a person’s hand.