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How Life on Earth Could Destroy Life on Mars

Could a virus or microbe from Earth screw up another planet's biosphere before we even discover it? Or could a Martian microbe brought back for scientific study spread an Andromeda Strain type of illness on Earth and wipe out humanity?
Image par NASA / JPL-Caltech / MSSS / James Sorenson

If NASA confirms that they have found liquid water on the planet Mars, it seems reasonable that we could send over the Curiosity Rover to poke around that water to search for life, right? Unfortunately, no: there's a little problem—or possibly a lot of little problems: microbes. The question is whose microbes will create the bigger problem: Mars or Earth's? This is the central problem a practice called "planetary protection" attempts to solve.


Everyone knows you'll die in space without a space suit. However the deadliness of space might be slightly oversold. For instance, astronauts recently found bacteria or "space plankton" living on the outside of the International Space Station. That's a place with no air and a lot of hard radiation. Of course the station isn't the only place microbes could survive beyond Earth. There are some icy moons around Jupiter and Saturn with no atmosphere, lots of harsh chemicals in the rocks, and hard radiation roasting the surface, but plenty of liquid water. And then there's rusty, dusty Mars, with its marginal atmosphere and briny water lurking beneath the surface. The solar system beyond Earth is pretty harsh, so how can you "contaminate" it? If Earth biology has taught us anything, it's that if you have liquid water, you can have life. And there appears to be water in all kinds of places out there.

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Dr. David Coil, a microbiologist at the University of California-Davis, explains the reason for concern: "Microbes are incredibly adaptable and can be found in the most unlikely of places [nuclear waste, outside the space station, inside rocks deep in the earth, etc]…I'd say that forward contamination [humans contaminating Mars] is quite likely."

It's like when you read about someone "contaminating the crime scene" or about bad cops planting evidence. In the case of Curiosity, there might be microbes attached to the robot that survived the NASA clean room, the vacuum of space, and the Martian atmosphere. If Curiosity were to roll through some actual Mars water and Earth bacteria got into it, scientists' questions will multiply faster than, well…bacteria: "Is that a native bacteria? How did it get there? Is it exactly the same species as the ones found on Earth? If it's Earth bacteria, how quickly will it multiply when exposed to water? Oh my gosh, what the heck have we done?!"


But say Earth microbes do get loose on Mars. Why would that be a problem?

"The biggest downside is screwing up the ecology of what is already there," Coil said. "Philosophically if there were no life on Mars, then I suppose there's still an argument for not getting earth junk all over it. But the much bigger concern to me is if there is life, and we ruin it before we even get a chance to understand it."

Given how adaptable life is in the imperfect deadliness of space, interplanetary cross-contamination keeps a lot of scientists up at night. Could a virus or microbe from Earth screw up another planet's biosphere before we even discover it? Could a Martian microbe brought back for scientific study spread an Andromeda Strain type of illness on Earth?

Until we determine whether life exists on Mars and how it behaves, space agencies keep their robots as clean as possible. According to the international folks who pay attention to this issue, this means having less than 30 total microbes per square meter on the surface of an Earth vehicle landing in "special areas" of Mars—those places where water or life is suspected to exist. To compare that to a normally clean environment, a hospital surface cleaned only with soap and water can have as many as 34,000 bacteria.

If we worry about the microbes that might be lurking in public toilets, shopping carts, drinking water, or the food we eat in familiar places on Earth, it sort of makes sense that we pay attention to what we bring home from another planet.


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Today we find it quaint that the original Apollo astronauts were sequestered in special isolation trailers when they returned from the Moon. That might seem like a bit of overkill, but in 1969 we didn't know that the Moon was lifeless and had no good way to check. The best approach anyone could think of was to keep Apollo 11, 12, and 14 astronauts isolated for three weeks to see if they caught Moon Fever or died or anything untoward. Also, while the Apollo astronauts were playing guinea pig, various plants and animals were exposed to lunar material to see if they were going to keel over. No doubt similar things could be done when astronauts return from Mars.

Dr. Robert Zubrin, President of the Mars Society and author of The Case for Mars, is a vocal advocate of sending humans to Mars within a decade. He is not a fan of the planetary protection rules.

"The obsession with planetary protection is now becoming an impediment to Mars exploration," he said, by making super-clean landers too expensive. In fact, Zubrin thinks the cross-contamination issue has already been overcome by events.

"We get about 500 kilograms of Mars material delivered in the form of meteorites every year. Aside from a dog that was killed by a falling meteorite in Egypt in 1911, nobody's died from any of them."

There cannot be pathogens on Mars, Zubrin stated, because there are no megafauna [i.e., large animals] to live off of. Dr. Coil agreed: "The risk of reverse contamination of any kind is so low that I don't think it's even worth worrying about."


Still, it might be premature to completely dismiss cross-contamination between worlds. This week an astrobiologist presented a paper claiming that life on Earth arrived from elsewhere. The scientist's theory is that the early progenitors of life — RNA proteins — combined with fatty materials brought by a meteor impact to form the first cells. Another scientist thinks that meteorite could have come from Mars, so maybe we're all Martians! How would we determine if Earth life is really Martian? Robert Zubrin suggested one theory: "If you find something that had the same RNA or DNA as life here, but was simpler than bacteria, that would show that Earth life originated on Mars."

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So is planetary protection a big deal or not? Right now, we can't get the answers we need about possible Mars life because the tools we need aren't there yet. For example, even if Curiosity were able to motor over to one of the briny splashes seen from space, the rover lacks the instruments to detect life — native or imported.

In the end, planetary protection isn't a matter of preventing life from traveling world to world. We want to send people to Mars and return samples (and living astronauts) to Earth. The question is whether or not we get crazy about how we protect ourselves from the unknown. We hope to find a Goldilocks approach here: we don't want a dead Mars, but we don't want too many aggressive life forms migrating back to Earth, either — just the right amount for our life form to learn something important about life in the universe.

Follow Bart Leahy on Twitter: @SciCheerGopher

Photo via Wikimedia Commons