How NASA Prevents Alien Life from Contaminating Earth—and Vice Versa

People love a good alien visitation story, whether it's a heart-warming depiction of friendship like E.T. or a frightening tale of hostile invasion like Independence Day.

But for Cassie Conley, NASA's planetary protection officer, keeping Earth safe from alien contamination isn't just fodder for science fiction; it's part of her job description.

As head of the agency's Office of Planetary Protection, Conley is tasked with ensuring that sample return trips to extraterrestrial environments—for instance, the recently launched OSIRIS-REx mission to asteroid Bennu—have a low risk of bringing alien life back to Earth.

Likewise, she ensures that Earth life does not hitchhike to potentially hospitable environments, like Jupiter's moon Europa or the watery regions of Mars, where it might thrive and create false positives of alien life.

As Conley succinctly put it in the New York Times: "If we're going to look for life on Mars, it would be really kind of lame to bring Earth life and find that instead."

READ MORE: NASA Is Scouring Mars to Find a Site for Its First Manned Base

So lame. But given how endurant and adaptable some of Earth's creatures have proven themselves to be (looking at you, tardigrades), there is a real possibility that they could tag along with interplanetary landers and set up shop on a brand new world.

"We have discovered that there are many more Earth organisms that have capabilities we didn't expect," Conley said in this new NASA video about planetary protection, released Sunday morning.

"If you had pizza last night, or if you put cheese on your salad last night or put cheese on your pasta, you probably have organisms in your mouth right now that could grow on Mars as long as they were protected from ultraviolet (UV) radiation, and they have some level of water and nutrients."

Indeed, we know that despite sterilization measures, the Curiosity rover had all kinds of microbial passengers onboard when it landed on the Martian surface, which is why the vehicle is not permitted to mosey over to nearby areas thought to be rich in water or nutrients. While these regions are the most tantalizing to study from an exobiological perspective, they are also the places most likely to give opportunistic Earth life a chance to take hold, a process known as forward contamination.

Backward contamination, meanwhile, describes the possibility of alien life from extraterrestrial worlds hitchhiking back to Earth on one of our sample return missions, or even taking up residence in the bodies of the first Mars-bound astronauts.

"There is a lot of interest in trying to get samples back from Mars, not just for the really cool science you would get, but also for this backward contamination issue," Richard Davis, the assistant director of science and exploration at NASA headquarters, told me last year. "It is low probability, but you can't dismiss it and you need to do due diligence on it so ensure that you are not putting your crew members, or even Earth, at risk."

To be sure, the notion of astronauts returning from Mars all doped up with weird alien beasties is not a particularly appealing one, though it might make a good horror flick. In real life, however, it's good to know that NASA is taking due precautions in preventing the spread of Earthlings to untouched environments, as well as the return of potential hazardous alien life to our own front doorstep.

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