Ancient bacteria may be “sleeping” on the surface of Mars


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Ancient bacteria could be lying dormant on the surface of Mars, shielded from the harsh radiation of space for millions of years, according to new research.

Although no evidence of life has been found on the red planet, researchers simulated Martian conditions in a laboratory to see how bacteria and fungi could survive. Scientists were surprised that the bacteria could have survived for 280 million years if buried and protected from the ionizing radiation and solar particles that bombard the Martian surface.

The findings suggested that if there is life on Mars, evidence of it may still lie dormant in the planet’s subsurface, a place that future missions could explore as they drill into the Martian soil.

Billions of years ago, Mars was probably a more hospitable environment for life, including its surface atmosphere and water, today the red planet is more like a frozen desert. The dry mid-latitudes of the planet have an average temperature of 80 degrees Fahrenheit (minus 62 degrees Celsius). And then there’s the constant threat of radiation because Mars has a thin atmosphere.

“There is no running water or significant water in the Martian atmosphere, so the cells and spores would dry out,” said Brian Hoffman, the Charles E. and Emma H. ​​Morrison Professor of Chemistry and professor of molecular biosciences at Northwestern University’s Weinberg College. Arts and Sciences, in a note. “It is also known that the surface temperature of Mars is similar to dry ice, so it is very icy.”

A research team determined the survival limits of microbial life when exposed to ionizing radiation like on Mars. The team then 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, nicknamed the “Conan bacterium” because of its hardy nature, seemed perfectly suited for life on Mars.

The bacterium is polyextremophilic, meaning it can survive harsh conditions such as dehydration, acid and cold temperatures. The hardy microbe is one of the most radiation-resistant known to science.

Previous studies have found that bacteria can survive for 1.2 million years on the surface of Mars amid the harsh radiation and dry, icy environment, longer than some microorganisms that survive for millions of years on Earth.

New research has determined that when Conan Bacteria is dried, frozen and buried on the surface of Mars, it can survive 140,000 units of radiation, 28,000 times the level of radiation exposure that can kill a human.

The bacteria, which look like a squash when viewed under a microscope, would likely survive only a few hours on the Martian surface after being exposed to ultraviolet light. The expected lifespan of the bacterium Conan 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) down.

The journal Astrobiology published a study detailing the findings on Tuesday.

The researchers were able to measure how much of the manganese antioxidant accumulated in the cells of the microorganisms exposed to radiation. The more manganese antioxidants the team found, the more likely the microbes would be able to withstand the radiation and survive.

The genomic structure of the Conan bacterium binds chromosomes and plasmids together, meaning cells stay aligned and can repair themselves after radiation exposure. And if a Conan-like microbe evolved on Mars billions of years ago, when water was still on the Martian surface, the remains of the bacteria may lie dormant in the planet’s subsurface.

“D. radiodurans buried in the Martian subsurface could not have survived between 2 and 2.5 billion years after the disappearance of water on Mars, as Martian environments regularly change and melt due to meteorite impacts,” said study author Michael Daly, Professor. of pathology at the Uniformed Services University of the Health Sciences and a member of the National Academies Committee on Planetary Protection, in a statement.

“We suggest that intermittent melting may allow for intermittent repopulation and dispersal. Also, if life on Mars ever existed, even if there are no viable life forms on Mars today, their macromolecules and viruses would last much longer. This strengthens the likelihood that, if life ever evolved on Mars, it will be revealed in future missions.’

The findings have implications for both the return of Martian samples to Earth and the landing of manned missions to Mars.

The Mars Sample Return program, an ambitious program led jointly by NASA and the European Space Agency, will launch multiple missions to Mars to receive and return samples collected by the Perseverance rover.

The rover team hopes that rock and soil samples taken from the site of an ancient lake and river delta in Mars’ Jezero Crater will determine whether life once existed on the red planet. Samples may also contain ancient microfossils.

Also, when astronauts land on Mars, they have the potential to unwittingly pick up bacteria that hitchhike from Earth.

“We concluded that ground-based contamination on Mars would be essentially persistent, 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 could survive to this day. This means that returning samples from Mars could contaminate Earth.’