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Dead stowaways landed on Mars in August 2012. That’s for certain. However, due to their diminutive size -- they were microbes -- it was easy to miss them as NASA’s Curiosity Mars rover touched down. Less certain, but much more consequential, is whether any Earth-based bacteria survived the trip with them. On Monday, scientists in Boston presented research strongly suggesting that they might have. Though long suspected, these results hold profound and costly consequences for upcoming NASA missions and, in the longer term, for how humans research, explore and perhaps even visit the Red Planet.

Since the dawn of the Space Age, scientists have worried about the potential for life forms from Earth to contaminate other worlds, thus skewing research into extraterrestrial life. That concern found its way into the 1967 Outer Space Treaty, which required spacefaring nations to avoid “harmful contamination” of the moon and other celestial bodies. In turn, NASA established an Office of Planetary Protection to preserve the ability to study planets in their natural states (and, importantly, to protect Earth from space-based contamination).

Since then, all U.S. spacecraft bound for other planets have been thoroughly sterilized prior to launch, often at great expense. During the Viking missions to Mars in the 1970s, for example, nearly 10 percent of the overall mission budget was spent on decontamination, according to one researcher. Nonetheless, nothing -- especially a large space probe -- can be sterilized completely. Thus, Mars Curiosity launched with 22 microbial spores per square meter -- well within NASA’s specifications.

The presumption was that none of those spores could survive the trip through interstellar space and the Martian atmosphere. Yet in advance of Curiosity’s launch, researchers swabbed the craft and identified 377 organisms representing 65 species of bacteria, which they subsequently attempted to culture under conditions approximating what might be experienced during a trip to Mars, including extreme temperatures and extensive exposure to ultraviolet radiation. Of the cultured strains, the study released this week concluded, “11 percent of isolates could survive under multiple extreme conditions.”

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