New research shows that many centuries ago, Mars probably had enough chemical energy for microbes to survive underground.
“We found, based on fundamental physical and chemical calculations, that the ancient Martian subsurface was likely to have enough dissolved hydrogen to power the global subsurface biosphere,” said Jesse Tarnas, a graduate student at Brown University who led the study. "The conditions in this zone could be similar to those areas on Earth in which underground life exists."
The earth is home to the so-called underground lithotrophic microbial ecosystems. Lacking energy from sunlight, these underground microbes often get it by separating electrons from molecules in their environment. Dissolved molecular hydrogen is a large electron donor.
New research shows that radiolysis, the process by which radiation breaks down water molecules into their constituent hydrogen and oxygen parts, would create large amounts of hydrogen in the ancient Martian subsurface zone.
The findings do not allow scientists to confidently assert that life on Mars existed, but they suggest that if life really originated, the Martian subsurface would have key components to maintain it for hundreds of millions of years. This research is also very important for the future exploration of Mars.
Going underground
Since the discovery of ancient river channels and lake beds on Mars a few decades ago, scientists have fired up the idea that the Planet of Fire could someday be made habitable. However, modern climate temperature models of ancient Mars show that temperatures were always extremely low. This suggests that the presence of moisture on the planet many centuries ago may have been a passing event. This is not the best scenario for sustaining surface life in the long term, and now some scientists believe that the subsurface may be the best environment for this.
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"The question arises: what was the nature of this underground life, if it existed, and where did it get its energy from?" - said Professor Jack Mustard, co-author of the study.
Through numerous calculations and a lot of analytical work, the researchers concluded that Mars probably had a global underground habitat several kilometers thick. In this zone, the production of hydrogen through radiolysis would generate more than enough chemical energy to support the life of microorganisms. According to scientists, this zone will remain for hundreds of millions of years.
“People have a well-established idea that the cold climate of Mars is harmful and even unsuitable for life, but the results of our research show that chemical energy does exist in this cold climate, making life underground more habitable than being on surface,”Tarnas reports. "We think this could change people's perception of the climate on Mars and the past of the planet as a whole."
Studied consequences
Tarnas and Mustard say the results of the study could be useful for thinking about where to send the spacecraft in search of signs of past life on Mars.
“One of the most interesting options for exploring is looking at blocks of megabreccia - chunks of stone that were thrown from beneath the surface after meteorite impacts,” Tarnas said. "Many of them were just in this habitable zone, and now they simply lie, almost unchanged, on the surface of the Fiery Planet."
Mustard, who was heavily involved in the selection of the landing site for the Mars 2020 spacecraft, says the blocks are located in at least two of the options NASA is considering on the planet: the northeastern and central parts.
“The mission of this rover will be to look for signs of a past life,” Mustard said. "Areas in which remnants of an underground habitable zone can be found, which may have been the largest such zone on Mars, are extremely interesting subjects to study."
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