Ancient bacteria might be sleeping beneath the surface of Mars, where it has been shielded from the harsh radiation of space for millions of years, according to new research.
Researchers simulated conditions on Mars in a lab to see how bacteria and fungi could survive even though no evidence of life has been found on the red planet.
To their surprise, scientists discovered that bacteria could likely survive for 280 million years if it were buried and protected from the ionizing radiation and solar particles that bombard the Martian surface.
The findings suggested that if life ever existed on Mars, its dormant evidence might still be located in the planet’s subsurface—a place that future missions could explore as they drill into the Martian soil.
The surface of Mars is like a frozen desert
Today, the red planet is more like a frozen desert, though Mars was likely a more hospitable environment for life with an atmosphere and water on its surface billions of years ago.
The planet’s arid midlatitudes have an average temperature of negative eighty degrees Fahrenheit (negative 62 degrees Celsius). There’s also the constant threat of radiation because Mars has such a thin atmosphere.
“There is no flowing water or significant water in the Martian atmosphere, so cells and spores would dry out,” said study coauthor Brian Hoffman, a Charles E. and Emma H. Morrison professor of chemistry and professor of molecular biosciences at Northwestern University’s Weinberg College of Arts and Sciences, in a statement.
“It also is known that the surface temperature on Mars is roughly similar to dry ice, so it is indeed deeply frozen,” he said.
Study determined survival limits of ancient bacteria
A research team determined the survival limits of microbial life when exposed to ionizing radiation as it might experience on Mars.
The team then 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 microbe called Deinococcus radiodurans and nicknamed “Conan the Bacterium” seemed perfectly suited to life on Mars due to its tough nature.
The hardy microbe is one of the most radiation-resistant organisms known to science. This is because it is a polyextremophile, which means it can survive harsh conditions such as dehydration, acid, and cold temperatures.
Previous research discovered that the bacteria could survive up to approximately 1.2 million years just beneath the surface of Mars amid the harsh radiation and dry, frozen, environment. It could, therefore, outlast certain microorganisms on Earth.
Ancient bacteria can survive intense levels of radiation
The new study determined that when Conan the Bacterium is dried, frozen, and buried deep beneath the Martian surface, it could survive 140,000 units of radiation, which is 28,000 times greater than the level of radiation exposure that could kill a human.
The bacteria, which resembles a pumpkin when viewed under a microscope, would likely survive only a few hours on the Martian surface after relentless exposure to ultraviolet light.
Conan the Bacterium’s expected survival increased to 1.5 million years just four inches (ten centimeters) below the surface and about 280 million years when buried thirty-three feet (ten meters) beneath the surface.
Study from the journal Astrobiology details bacteria survival
Researchers were able to measure the number of manganese antioxidants that accumulated in the cells of the microorganisms as they were exposed to radiation.
The more manganese antioxidants the team found, the more likely the microbe was to be able to resist the radiation and survive.
Conan the Bacterium’s cells remained in alignment and could repair themselves after radiation exposure since its genomic structure links chromosomes and plasmids together.
The bacteria’s dormant remnants might just be slumbering deep within the planet’s subsurface if a microbe similar to Conan evolved on Mars billions of years ago when water still existed on the Martian surface.
Information about ancient bacteria on Mars
Study author Michael Daly, a professor of pathology at Uniformed Services University of the Health Sciences and member of the National Academies Committee on Planetary Protection, said in a statement:
Although D. radiodurans buried in the Martian subsurface could not survive dormant for the estimated 2 to 2.5 billion years since flowing water disappeared on Mars, such Martian environments are regularly altered and melted by meteorite impacts.
We suggest that periodic melting could allow intermittent repopulation and dispersal. Also, if Martian life ever existed, even if viable lifeforms are not now present on Mars, their macromolecules and viruses would survive much, much longer.
That strengthens the probability that, if life ever evolved on Mars, this will be revealed in future missions.
Samples of ancient bacteria taken from Mars
An ambitious program, called The Mars Sample Return Program, jointly steered by NASA and the European Space Agency will launch multiple missions to Mars to collect and return samples that were gathered by the Perseverance rover.
The rover team hopes that the rock and soil samples could determine if life ever existed on the red planet.
The samples, which will be taken from the site of an ancient lake and river delta in the Jezero Crater of Mars, might even contain microfossils of ancient microbial life.
Rovers—rather than astronauts—to take samples from Mars
Additionally, astronauts have the potential to accidentally deliver hitchhiking bacteria from Earth when they land on Mars.
“We concluded that terrestrial contamination on Mars would essentially be permanent— over timeframes of thousands of years,” Hoffman said.
“This could complicate scientific efforts to look for Martian life,” he said. “Likewise, if microbes evolved on Mars, they could be capable of surviving until present day. That means returning Mars samples could contaminate Earth.”
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