Could there be life on Mars? It is the “big question” that we have been asking ourselves for a long time. Mars has an incredibly thin atmosphere, about 0.6 percent of Earth’s, which means it’s constantly bombarded by intense solar and galactic cosmic radiation. Now, a team of scientists claims that a bacterium called Deinococcus radiodurans (also known as Conan, the bacterium) could survive 280 million years on Mars, nearly 300 times longer than previously assumed, if it were buried some 10 meters below. from the surface of the Red Planet, shielded from radiation.
The most resistant bacteria in the world
Conan the bacterium is even listed in the Guinness Book of Records as the world’s hardiest known bacterium . Something like a super hero from the world of microorganisms.
The researchers exposed six types of terrestrial bacteria and fungi (including Conan the bacterium) to a dry, frozen, simulated Martian surface , and applied gamma rays or protons to mimic radiation in space. They also exposed the samples to much smaller doses than would occur if a microorganism were deeply buried . They found that Conan the bacterium survived astronomical amounts of radiation in the arid, icy environment, far outperforming Bacillus spores, which can survive on Earth for millions of years. Apparently their chromosomes are locked together , keeping them in perfect alignment and ready to repair themselves after intense radiation.
A bacterium like Conan the bacterium could withstand 140,000 grays (Gy) of radiation, 28,000 times more than would kill a human. Buried 10 cm below the Martian surface, the survival period would be 1.5 million years, but at 10 meters deep, it could survive a whopping 280 million years, the researchers say. That means a similar bacterium that evolved when running water still existed on the surface of Mars could still be dormant below the surface of the Red Planet.
The results of the current study published in the journal Astrobiology prove that certain strains of bacteria can survive even in the harsh environment of Mars , raising the possibility that future manned missions could contaminate the Red Planet and bring Martian bacteria back to Earth. . But it also means that future missions (such as ExoMars or the Mars Life Explorer) are more likely than we previously thought to find bacterial life.
“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,” explained Michael Daly . , a professor of pathology at the Uniformed Services Health Sciences University (USU) and a member of the Planetary Protection Committee of the National Academies, who led the study. “We suggest that periodic melting could allow intermittent repopulation and dispersal. Furthermore, if Martian life ever existed, even if there are no viable life forms on Mars now, its macromolecules and viruses would survive much, much longer. That strengthens the likelihood that if life ever evolved on Mars , this will be revealed in future missions.”
the negative side
“Our model organisms serve as proxies for both the forward contamination of Mars and the backward contamination of Earth, both of which must be avoided,” says Daly.
“We concluded that terrestrial contamination on Mars would be essentially permanent, over time periods of thousands of years,” says Brian Hoffman, co-author of the paper. “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. That means that returning samples from Mars could contaminate the Earth”, clarifies the expert.
Why is this study important?
NASA and the European Space Agency (ESA) aim to bring samples from Mars to Earth sometime in the 2030s thanks to their ambitious Mars Sample Return mission. When they do, they will be looking for these possible sleeping bacteria. Will we find microbial life in samples from Mars?
Referencia: “Effects of desiccation and freezing on microbial ionizing radiation survivability: Considerations for Mars sample-return” 25 October 2022, Astrobiology.
The study was supported by the Defense Threat Reduction Agency (grant number HDTRA1620354) and the National Institutes of Health (grant number GM111097).