If There Are Microbes on Mars, We Might Have Put Them There

Microbes stick to spacecraft, but are they hardy enough to survive the journey?

May 20 2014, 7:20pm
Image: NASA/JPL-Caltech

If we find evidence of life on Mars, it could be because we put it there. That’s one implication of a study conducted by researchers who looked at microorganisms collected from the Curiosity rover currently trundling across the Martian landscape.

NASA’s Jet Propulsion Library invited researchers from the University of Idaho to look at their full archive of microbes collected from swabs taken off Curiosity before it launched into space, to learn more about potential microorganism stowaways on spacecraft. They presented their findings at the 2014 American Society for Microbiology meeting.

“From a research perspective, what we were interested in knowing was where exactly they had been cultured off of the spacecraft, what type of organisms are on the spacecraft, and do they actually pose a threat to planetary protection or not? Is there any way these organisms could even survive a trip to Mars or would they all die on the way there?” Stephanie Smith, who led the work, told me. Nature reports that they identified 377 strains in total, and more than half of those belonged to the Bacillus genus.

What was most striking was how hardy some of the microbes were; they persisted through thorough cleanings. “In some cases the spacecraft has been cleaned as many as 50 times, yet they're still getting microorganisms off the spacecraft,” said Smith. Notably, around a third weren’t spore-forming, which meant they had to have some other form of protection. 

To test quite how tough the bugs were, her team subjected some of the microbes to harsh environmental conditions like increased salt or pH levels, cold temperatures, and UV-C radiation (which is often used to sterilise bacteria). Many even survived after being desiccated for two weeks and then rehydrated. The researchers reported that 11 percent withstood multiple extremes.

The question then, of course, is: Could they survive on other planets? Smith said more work will have to be done to answer that one, but explained that many of the microbes studied were capable of surviving off substrates found on Mars like sulfate, perchlorate, and iron. 

If we are taking microbes to Mars, that could pose obvious problems when it comes to the search for extraterrestrial life. How could we tell if a microbe picked up by a mission originated on Mars, or if it had traveled all the way from Earth and back?

“If we’re looking for life on other planets, there’s a possibility for the microbes on the spacecraft to hinder that search,” Smith confirmed. “If we were for instance to find signs of life, it could be difficult to distinguish whether it was from organisms from earth on the spacecraft or if it was actually Martian life.”

There’s also the issue that the Outer Space Treaty prohibits the contamination of other planets by Earth life, so we need to keep a check on microbial hitchhikers. Smith said that we need to develop better cleaner methods, and her team are now looking at the kind of reagents that do and don’t work in that respect. Motherboard’s Ben Richmond wrote earlier this month about NASA’s need to find a new way to kill bacteria, based on other studies that also found they could survive surprisingly tough conditions.

They’ve also proposed sending some of the microbes they investigated up to the International Space Station to see how they behave there.They were separately involved with the recent MERCURRI mission that saw SpaceX’s Falcon 9 launch a cohort of microbes up to the ISS last month.

On a broader level, they’re trying to explore how these microbes are so resistant to extreme environments, as the one firm conclusion they can draw from their work so far is that these microbes are very hardy. “We need to take precautions until we know more about these organisms,” said Smith.