The Martian surface is harsh, a dry, cold, irradiated environment. But ancient Mars may have been habitable for microbial life because it supported water. The rovers going to Mars in the coming years will be searching for biosignatures in Martian soil, drilling and sampling below the surface to find evidence of this potential ancient life.
A NASA-funded study deployed a robotic rover in the Atacama Desert in 2013 for a trial mission to find signs of life in another inhospitable environment. The Atacama Desert is the driest desert region on Earth, with incredibly little moisture or precipitation. Animals and plants are hard to come by, but bacteria could be below the surface.
The study results were published Thursday in the journal Frontiers in Microbiology.
"The core of the Atacama Desert in Chile is extremely dry, experiencing decades without rainfall," Stephen Pointing, study author and director of the science division at Yale-NUS College in Singapore, said in a statement. "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,"
The autonomous solar-powered rover traveled 50 kilometers over two types of terrain similar to what it might encounter on Mars. One was stony desert pavement, and the other was sandy and typical of the desert environment. The rover also used a drill to collect 32 samples 80 centimeters below the surface.
"We have shown that a robotic rover can recover subsurface soil in the most Mars-like desert on Earth," 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."
In addition to the drill, the rover can map and analyze the landscape, the visible habitat and even geochemical features thanks to its mounted cameras and spectrometer.
The rover found patches of unusual microbes that were highly specialized. The researchers believe that the patchy distribution is because of the soil's chemistry and the lack of nutrients and water.
They compared the rover's samples with those that they took from the desert manually. The microbial life was similar in both types of samples.
"We found microbes adapted to high salt levels, similar to what may be expected in the Martian subsurface," Pointing said. "These microbes are very different from those previously known to occur on the surface of deserts."
Understanding the distribution of life in the Atacama Desert could help with the strategy of the rovers deployed on Mars.
"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," study co-authors Nathalie Cabrol and Kim Warren-Rhodes of the SETI Institute said in a statement. "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."
In the future, rovers will need to be able to drill deeper. Future studies will need to explore those capabilities.
"Mars missions hope to drill to approximately [2 meters] and so having an Earth-based comparison will help identify potential problems and the interpretation of results once rovers are deployed there," the researchers said. "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."
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