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Ancient bacteria may be sleeping beneath the surface of Mars, where it has been shielded from harsh space radiation for millions of years, new research suggests.
Although no evidence of life was found on the Red Planet, researchers simulated conditions on Mars in a lab to see how bacteria and fungi could survive. Scientists were surprised to discover that the bacteria could probably survive for 280 million years if they were buried and protected from the ionizing radiation and solar particles that bombard the Martian surface.
The results suggest that if life ever existed on Mars, latent evidence of it could still be located in the planet’s subsurface – a place that future missions could explore by drilling into Martian soil.
While Mars was probably a more hospitable environment for life billions of years ago, including an atmosphere and water on its surface, today the Red Planet looks more like a frozen wasteland. The planet’s arid mid-latitudes have an average temperature of minus 80 degrees Fahrenheit (minus 62 degrees Celsius). And then there’s the constant threat of radiation because Mars has such a thin atmosphere.
“There is no running water or significant water in the Martian atmosphere, so the cells and spores dry out,” said study co-author Brian Hoffman, professor of chemistry. Charles E. and Emma H. Morrison and Professor of Molecular Biosciences at Weinberg College at Northwestern University. of Arts and Sciences, in a press release. “The surface temperature on Mars is also known to be roughly similar to dry ice, so it is indeed deeply frozen.”
A research team has determined the survival limits of microbial life when exposed to ionizing radiation as it might experience on Mars. Next, the team introduced six types of bacteria and fungi found on Earth into a simulated Martian surface environment, while zapping them with protons or gamma rays to mimic space radiation.
A clear winner emerged called Deinococcus radiodurans. The microbe, dubbed “Conan the Bacteria” because of its tough nature, seemed perfectly adapted to life on Mars.
The bacterium is polyextremophilic, which means it can survive harsh conditions such as dehydration, acidic and cold temperatures. The hardy microbe is one of the most radiation resistant organisms known to science.
Previous research has shown that the bacterium could survive 1.2 million years just below the surface of Mars amid harsh radiation and the dry, frozen environment – and survive some microorganisms known to survive on Earth for millions of years.
The new study determined that when Conan bacteria is dried, frozen and buried deep below the Martian surface, it can survive 140,000 units of radiation, 28,000 times more than the level of radiation exposure that could kill a human. .
The bacterium, which looks like a pumpkin seen under a microscope, would likely only survive a few hours on the Martian surface after relentless exposure to ultraviolet light. The predicted survival of Conan the bacterium increased to 1.5 million years just 4 inches (10 centimeters) below the surface, and about 280 million years if the bacterium was 33 feet (10 meters) deep. .
The journal Astrobiology published a study on Tuesday detailing the findings.
The researchers were able to measure the number of manganese antioxidants accumulated in the cells of the microorganisms when they were exposed to radiation. The more manganese-based antioxidants the team found, the better the microbe was able to withstand radiation and survive.
The genomic structure of Conan the bacterium connects chromosomes and plasmids, which means cells stay aligned and can repair themselves after exposure to radiation. And if a microbe similar to Conan evolved on Mars billions of years ago, when water still existed on the surface of Mars, the dormant remnants of the bacterium might just be sleeping deep in the planet’s subsoil. .
“Although the D. radiodurans buried in the Martian subsoil could not survive in dormancy for the estimated 2 to 2.5 billion years since the disappearance of running water on Mars, these Martian environments are regularly weathered and melted by meteor impacts,” said study author Michael Daly, Professor. of Pathology at Uniformed Services University of the Health Sciences and a member of the National Academies Committee on Planetary Protection, in a statement.
“We suggest that periodic melting could allow intermittent restocking and dispersal. Moreover, if Martian life existed, even if viable life forms are not present on Mars, their macromolecules and viruses would survive much, much longer. This reinforces the likelihood that, if life ever evolved on Mars, it would reveal itself in future missions.
The findings have implications for both returning Martian samples to Earth and landing crewed missions on Mars.
The Mars Sample Return program, an ambitious program piloted jointly by NASA and the European Space Agency, will launch multiple missions to Mars to collect and return samples that were collected by the Perseverance rover.
The rover team hopes rock and soil samples, taken from the site of an ancient lake and river delta in Mars’ Jezero Crater, could determine whether life ever existed on the Red Planet. The samples could even contain microfossils of ancient microbial life.
Additionally, astronauts have the potential to accidentally deliver bacteria hitchhiking from Earth when they land on Mars.
“We concluded that terrestrial contamination on Mars would be essentially permanent — over periods of thousands of years,” Hoffman said. “This could complicate scientific efforts to search for Martian life. Likewise, if microbes evolved on Mars, they might be able to survive to the present day. This means that returning samples from Mars could contaminate Earth.
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