A simulated mission in the Chilean desert shows how a rover could detect life on Mars


A NASA test mission in the Atacama Desert, similar to Mars.
Image: Stephen Pointing

Using the arid desert of Atacama in Chile as a Mars replacement, researchers have shown that it is possible to use a rover-mounted standalone drill to detect life beneath a desolate surface. Encouragingly, the test revealed a resistant microorganism – exactly the kind of creature that could hide under the Martian surface.

A new study published today in Frontiers in Microbiology describes a NASA test mission in the Atacama Desert in Chile, which could reflect a future mission on Mars. The experimental rover and drill, designed by the Carnegie Mellon Institute of Robotics and funded by NASA, has recovered microorganisms below the surface, particularly a salt-resistant bacterium. The test helped justify a hunting mission to life on Mars, but the experiment was not without challenges or limitations. As the new study shows, finding life on Mars – if it already exists – will require serious technological innovations, a lot of money and a bit of luck.

Billions of years ago, Mars had a temperate climate and liquid water on its surface, providing a potential environment for life. Today, life is unlikely to exist on the surface. Deadly radiation bathes the red planet and its tortured surface contains few traces of liquid water. During the Martian summer, daytime temperatures near the equator can reach 20 degrees Celsius (68 degrees Fahrenheit), but at night fall to -100 degrees C (14 degrees F).

The robotic drill of the rover used in the Atacama desert.
Image: Stephen Pointing

Sub-surface conditions are another story, according to Stephen Pointing, a researcher at Yale-NUS College in Singapore and lead author of the new study. Just below the surface, rocks and sediments provide shelter from extreme conditions, providing a potential habitat for life.

As Pointing explained to Gizmodo, there is no place on Earth comparable to the surface of Mars, but the ground beneath the Atacama desert in Chile offers a decent analogue.

"Some of the most Mars-like soils are found in the Atacama Desert," said Pointing. "There is very little water in the desert and soils have become very nutrient-poor and extremely salty over time, and they chemically resemble soils on Mars in many ways. In anticipation of future missions to Mars, we use sites such as the Atacama Desert to test theories of the distribution of life and new technologies to search for life. "

For the experiment, Pointing and his colleagues deployed a four-wheel autonomous robot equipped with a robotic drill, which allowed to recover sediment samples below the surface to a depth of 80 centimeters (31 inches) . The researchers compared the samples collected by the mobile to the samples taken by hand. Then, using DNA sequencing, Pointing and his colleagues showed that the bacterial life in the sediments recovered by the two methods was similar, which showed that the technique of the mobile was a success.

That said, the bacteria were not evenly distributed in the desert, but were rather in apparently random areas. This was due to "the limited availability of water, rare nutrients and soil geochemistry," said Pointing, adding that "in the search for life on Mars," we could be confronted with the biggest A problem of haystack.

Nevertheless, the new study is the first to show that microorganisms are distributed in specific living areas of the subsurface below the surface of the Atacama Desert.

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"The surface supports an ubiquitous and banal community dominated by photosynthesis Chloroflexi and these have been widely reported before, "Gizmodo told Pointing. "It's just beneath the surface that it's starting to get interesting. We have seen that with increasing depth, the bacterial community was dominated by bacteria able to thrive in extremely salty and alkaline soils. In turn, they were replaced up to 80 cm deep by a unique group of bacteria that survive by metabolizing methane as a food source. "

It is interesting to note that new research shows that Atacama's subsoil can support highly specialized microbes that could potentially survive on Martian saline soil. In addition, Mars is known to contain large amounts of methane on the surface, indicating the possible presence of methane-absorbing microorganisms beneath the Martian surface, according to the new document. An important step for Pointing and his team will be to understand how Atacama's underground microbes can survive. To this end, they are studying the possible strategies used by bacteria to survive for long periods without water and in extremely salty conditions. In addition, the team would like to return to the Atacama Desert with a vehicle capable of drilling up to 2 meters (6 feet) deep.

That said, it's time to do some checks in the facts.

The researchers have successfully used a probe to detect life on Earth, which is certainly not terribly difficult, even when the environment is a desert. Life has blossomed on the Earth for billions of years and is ubiquitous even in rocks thousands of feet below the surface. Yes, the new search was done at a place similar to Mars, but it's still not Mars. At best, the new study presents a scientific rationale for a future life-search mission on the Red Planet, but any speculation about life on Mars remains the same.

Another important limitation of the new research is that the sediment samples have been tested in the laboratory and not by material on the mobile itself. Pointing to itself, this would be a major obstacle for Mars mission planners.

"For a rover on Mars, it's hard to identify any unmistakable signs of life," said Pointing. "The DNA sequencing method we used is excellent here on Earth, but it is currently too complex to function reliably on Mars. This is why the indirect detection of other molecules known to be formed by living cells is probably the approach to which missions to Mars will go in the short term. "

In other words, it would be more logical for a mobile future to look for biosignatures – remnants of biological life, such as inexplicable traces of molecular oxygen associated with methane, piles of accumulated microbes (stromatolites), and traces fossilized waste, fat and steroids. If anything like this could be detected, "then we would need new experimental techniques to check if a Martian bacteria was actually alive and capable of an active metabolism," Pointing said.

Finally, and perhaps more discouragingly, there is the cost of sending such a mission to Mars. NASA and ESA plan to send robots to Mars in the coming years, but it is unclear whether either agency has the technological capability or the funds to organize a mission capable of restoring samples of rocks and Martian soils on Earth for analysis. As SpaceNews reported this week, it is unlikely that NASA will return samples of Mars in the 2020s, mainly because of expenses.

Pointing admitted that a return mission would be expensive, and would cost hundreds of millions of dollars.

"However, the research will help us answer one of the biggest questions we may ever ask," he said. "Is the Earth the only planet that supports life?"

[Frontiers in Microbiology]
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