Could subterranean microbes be found on Mars?

A robotic rover deployed in the most Mars-like environment on Earth, the Atacama Desert in Chile, has successfully recovered subsurface soil samples during a trial mission to find signs of life. The study’s findings, published in the journal Frontiers in Microbiology, will aid the search for evidence of signs of life during future planned missions to Mars.

In 2020, both NASA and the European Space Agency will embark on missions to deploy rovers on the surface of Mars. They will search for evidence of past or present life and, for the first time, drill below the surface where refuges for simple microbial life may still exist. To help ensure that these space missions succeed, technology is rigorously tested on Earth first.

“The core of the Atacama Desert in Chile is extremely dry, experiencing decades without rainfall,” said Professor Stephen Pointing, from Yale-NUS College, who led the microbial research. “It has high surface UV radiation exposure and is comprised of very salty soil. It’s the closest match we have on Earth to Mars, which makes it good for testing simulated missions to this planet.”

An autonomous rover-mounted robotic drill and sampling device, funded by NASA and designed by the Robotics Institute at Carnegie Mellon University, was deployed in the Atacama Desert to test if it could successfully recover sediment samples down to a depth of 80 cm. Prof Pointing and his colleagues compared samples recovered by the rover to soil samples carefully taken by hand. Using DNA sequencing, the researchers found that the unusual and highly specialised microbes in the sediments recovered by both methods were similar, indicating a successful deployment.

“We have shown that a robotic rover can recover subsurface soil in the most Mars-like desert on Earth,” Prof Pointing said. “This is important because most scientists agree that any life on Mars would have to occur below the surface to escape the harsh surface conditions where high radiation, low temperature and lack of water make life unlikely.

“We found microbes adapted to high salt levels, similar to what may be expected in the Martian subsurface. These microbes are very different from those previously known to occur on the surface of deserts.”

The results also revealed that microbial life was very patchy and related to the limited water availability, scarce nutrients and geochemistry of the soil. According to study co-authors Nathalie Cabrol and Kim Warren-Rhodes, from the SETI Institute, “These results confirm a basic ecological rule that microbial life is patchy in Earth’s most extreme habitats, which hints that past or present life on other planets may also exhibit patchiness.

“While this will make detection more challenging, our findings provide possible signposts to guide the exploration for life on Mars, demonstrating that it is possible to detect life with smart robotic search and sampling strategies.”

According to Prof Pointing, future research will include drilling deeper to understand just how far down recoverable microbes occur. He noted, “Mars missions hope to drill to approximately 2 m and so having an Earth-based comparison will help identify potential problems and the interpretation of results once rovers are deployed there.

“Ecological studies that help us predict the habitable areas for microbial communities in Earth’s most extreme environments will also be critical to finding life on other planets.”

Image caption: A trial NASA rover mission in the Mars-like Atacama Desert. Image credit: Professor Stephen B Pointing.

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