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Ancient bacteria could be sleeping beneath the surface of Mars, where it has been protected from the harsh radiation of space for millions of years, according to new research.
Since no evidence of life has been found on the red planet, researchers simulated conditions on Mars in the lab to see how bacteria and fungi could survive. The scientists were surprised to discover that the bacteria could have likely existed for 280 million years if it had been buried and protected from ionizing radiation and solar particles that bombarded the surface of Mars.
The findings suggested that if life had ever existed on Mars, its dormant evidence could still be located in the planetary subsurface, a place that future missions could explore while drilling into the Martian soil.
While Mars was likely a hospitable environment for life billions of years ago, with an atmosphere and water on the surface, today the red planet is more like an icy desert. the average temperature of the arid midlatitudes of the planet is minus 80 degrees Fahrenheit (minus 62 degrees Celsius). And then there is the persistence of radiation because Mars has such an atmosphere.
“There is no water flow or significant water in the Martian atmosphere to dry out cells and spores,” said study co-author Brian Hoffman, the Charles E. and Emma H. Morrison Professor of Chemistry and professor of molecular biology at Northwestern University’s Weinberg College. on the constitution of Arts and Sciences. “It is also known that the surface temperature on Mars is almost like that of dry ice, so it is completely frozen.”
The research team established the survival limits of microbial life when exposed to ionizing radiation, as might be experienced on Mars. Then the team introduced six types of bacteria and fungi found on Earth to a simulated Martian surface environment — all while zapping them with protons or gamma rays to mimic space radiation.
A famous winner emerged, called Deinococcus radiodurans. The microbe, nicknamed the “Conan bacterium” because of its tough nature, seemed well-suited to life on Mars.
It is a polyextremophilic bacteria, meaning it can survive harsh conditions such as drought, acids and cold temperatures. The hard microbe is one of the most radio-resistant organisms known to science.
Previous research has found that bacteria have survived 1.2 million years under the surface of Mars amid harsh radiation and a dry, frozen environment — and that some microorganisms are known to have survived on Earth for millions of years.
A new study has determined that when the Conan bacterium is completely dried, frozen and buried under the Martian surface, it can survive 140,000 signals of radiation — 28,000 times greater than the level of radiation exposure that could kill a human.
The bacteria, which look like a pumpkin when viewed under a microscope, are likely to survive a few hours on the Martian surface after relentless exposure to ultraviolet light. Conan’s bacterium is expected to survive up to 1.5 million years only 4 inches (10 centimeters) below the surface, and about 280 million years if the bacteria went down 33 feet (10 meters).
The Journal of Astrobiology published the findings on Tuesday.
The researchers were able to measure how much manganese was readily accumulated in the cells of the microorganisms as they were exposed to radiation. The more manganese the team found, the more the microbe was able to resist radiation and survive.
Conan’s genomic structure links chromosomes and plasmids together, meaning cells can remain diverse and repair themselves after radiation exposure. And if microbes like Conan evolved on Mars billions of years ago, when water still existed on the Martian surface, the remnants of the bacteria could just be sleeping deep in the planet’s sediments.
“Although D. radiodurans buried in the Martian subsurface could not survive dormant for the estimated 2 to 2.5 billion years when water flowing on Mars disappeared, such environments are regularly altered and melted by Martian meteorite impacts,” said study author Michael Daly, professor. of pathology at the Uniformed Services University of the Health Sciences and member of the National Academies’ Committee on Planetary Protection, in a statement.
“We suggest that periodic melting could have allowed intermittent abrogation and dispersal. Even if Martian life has ever existed, even if viable life forms are no longer present on Mars, their macromolecules and viruses will survive much, much longer. This confirms that it is more likely that if life ever existed on Mars has been developed, this will be revealed in future missions.
The findings have implications for returning Mars samples to Earth, as well as for sending missions to Mars.
The Mars Sample Return program, an ambitious project jointly run by NASA and the European Space Agency, will send several missions to Mars to collect and return samples collected by the Perseverance rover.
The rover hopes that rock and soil samples, taken from the site of an ancient lake and river delta in the Martian Lake Crater, will be able to determine if life ever existed on the red planet. The samples could also contain microfossils of ancient microbial life.
In addition, astronauts have the potential to accidentally release hitchhiking bacteria from Earth when they land on Mars.
“We concluded that terrestrial contamination on Mars is essentially permanent — over periods of thousands of years,” Hoffman said. “This could complicate scientific efforts to search for life on Mars. Likewise, if microbes evolved on Mars, they may be capable of surviving to this day. That way returning Mars samples could contaminate Earth.”
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