An artist's rendering of the conceptual design for a robotic probe on the surface Europa. 

Michael Carroll for Jet Propulsion Laboratory/NASA

How to protect Europa from earthlings

BOSTON—In less than a decade, NASA will send a spacecraft to Jupiter’s moon Europa. Once there, a lander will navigate the world’s icy surface for about 20 days and attempt to probe its hypothesized vast subsurface ocean. But whether Europa contains life, how can we avoid contaminating it with our own? That was the focus of a session here yesterday at the annual meeting of AAAS, which publishes Science
Part of the problem, said session speaker Norine Noonan, a biologist at the University of South Florida in Tampa who previous served as chair of NASA’s Planetary Protection Advisory Committee, is that humans are “autonomous microbial growth distribution systems.” Our bodies “spew fountains of bacteria,” she told attendees, and these microbes hitch rides on sensitive space equipment despite efforts to sterilize it. “If you take a $2 billion rover to Mars to study the organic microbes you brought with you, it’s not cost effective.”
Such organic pollution isn’t just bad science. It also violates Article IX of the Outer Space Treaty of 1967, which mandates the exploration of “the moon and other celestial bodies so as to avoid their harmful contamination and also adverse changes in the environment of the earth resulting from that introduction of extraterrestrial matter.” 
“Planetary protection doesn’t affect most of the proposals NASA’s going to get,” John Rummel, a biologist at the Search for Extraterrestrial Intelligence Institute in Mountain View, California, who organized the session, tells Science. “Just missions that want to bring back samples and flagship missions to Europa and Mars.”
So how can we avoid bringing little green microbes to Europa’s little green men? Kevin Hand, an astrobiologist at NASA’s Jet Propulsion Laboratory in Pasadena, California, writes in an email that his team plans to build the Europa lander in a clean facility, then “bake out” any remaining microbes by bombarding it with high heat. The spacecraft is then wrapped in a biobarrier, an aluminum foil–like sheath that keeps out any errant contaminants until it reaches Jupiter's moon. These strategies have been “implemented before, so there is good heritage for our approach,” he says.
According to Rummel, this is the first time since the Viking missions to Mars in 1975 that a full-system sterilization—meaning every component of the spacecraft—is planned for a planetary lander. “It probably costs about 10% more to design it [the spacecraft] like this,” he says. But the cost is worth it.
“Whatever lands on the surface of Europa will have less than a one in 10,000 chance of contaminating its surface,” Hand told attendees. “We have to protect Europa for Europans.” 
Check out our full coverage of AAAS 2017.