Microbes may have survived for millions of years under the surface of Mars

Ancient bacteria may lie dormant under the surface of Mars, where they have been shielded from the harsh radiation of space for millions of years, according to new research.

While no evidence of life has been found on the red planet, the researchers simulated conditions on Mars in a lab to see how bacteria and fungi might survive.

Scientists were surprised to find that it was possible that bacteria could survive for 280 million years if they were buried and protected from the ionizing radiation and solar particles that bombard the Martian surface.

The findings suggest that if life once existed on Mars, dormant evidence of it could still be located deep underground — a place that future missions could explore as they drill into the Martian soil.

While Mars was probably a more hospitable environment for life billions of years ago, with an atmosphere and water on its surface, today the red planet is more like a frozen wasteland. The planet’s arid mid-latitudes have an average temperature of -62 degrees Celsius. And there’s still the constant threat of radiation because Mars has a very thin atmosphere.

“There is no flowing water or significant water in the Martian atmosphere, so cells and spores would dry out,” said study co-authors Brian Hoffman, Charles E. and Emma H. ​​Morrison, Professor of Chemistry and professors of molecular bioscience at the Weinberg College of Arts and Sciences, from Northwestern University, in note.

“It is also known that the surface temperature of Mars is almost similar to dry ice, so it is in fact deeply frozen.”

A research team has determined the limits of survival of microbial life when exposed to ionizing radiation, as can occur on Mars. Next, the team introduced six types of bacteria and fungi found on Earth to a simulated Martian surface environment — all while testing them with protons or gamma rays to mimic space radiation.

A clear winner emerged. Called Deinococcus radioduransthe microbe, nicknamed “Conan the bacterium” because of its tough nature, seemed perfectly suited to life on Mars.

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

Previous research has found that bacteria can survive 1.2 million years just below the surface of Mars amid harsh radiation and a dry, frozen environment — and outlive some microorganisms known to survive on Earth for millions of years as well.

The new study determined that when the Conan bacterium is dry, frozen and buried deep beneath the Martian surface, it can survive 140,000 units of radiation — 28,000 times the level of radiation exposure that could kill a human. .

The bacterium, which resembles a pumpkin when viewed under a microscope, would likely survive just a few hours on the Martian surface after relentless exposure to ultraviolet light.

The expected survival of the Conan bacteria increased to 1.5 million years just 10 centimeters below the Martian surface and about 280 million years if the bacteria were 10 meters deep.

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

The researchers were able to measure how many manganese antioxidants 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 resist radiation and survive.

The genomic structure of the Conan bacteria joins chromosomes and plasmids together, which means that the cells remain aligned and can repair themselves after exposure to radiation. And if a Conan-like microbe evolved on Mars billions of years ago, when water still existed on the Martian surface, the dormant remnants of the bacteria could be sleeping deep beneath the planet’s subsurface.

“Although D. radiodurans buried in the Martian subsurface may not have survived dormant for the estimated 2 to 2.5 billion years since flowing water disappeared on Mars, these Martian environments are regularly altered and melted by meteorite impacts,” said study author Michael Daly, professor of pathology at the Uniformed Services University of the Health Sciences and member of the Planetary Protection Committee of the National Academies.

“We suggest that periodic melting could allow for intermittent repopulation and dispersal. Furthermore, if Martian life existed, even if viable life forms were not present on Mars, its macromolecules and viruses would survive much, much longer. This reinforces the likelihood that if life 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 on Mars.

The Mars Sample Return program, an ambitious program jointly run by NASA and the European Space Agency, will launch several missions to Mars to collect and return samples that were 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, can determine whether life once existed on the red planet. Samples may even contain microfossils of ancient microbial life.

Furthermore, astronauts have the potential to accidentally deliver bacteria that hitchhike from Earth when they land on Mars.

“We concluded that terrestrial contamination on Mars would be essentially permanent – over thousands of years,” said Hoffman. “This could complicate scientific efforts to look for Martian life. Likewise, if microbes evolved on Mars, they might be able to survive to the present day. This means returning samples from Mars could contaminate Earth.”