Scientists have put a number on how long they believe microorganisms can survive on Mars.

A team of researchers from Lomonosov Moscow State University, Faculty of Soil Science, has begun to piece together to what extent microorganisms can resist the extreme factors on Mars, which could help scientists assess the possibility of microorganisms and biomarkers surviving in various objects inside the Solar System.

The researchers studied the radiation resistance of microbial communities in permafrost sedimentary rocks under low temperature and low pressure. These sedimentary rocks are considered to be a terrestrial analog of regolith, the ground left after space weathering. The scientists assume that the potential Martian biosphere could survive in cryoconservated state, and that the main factor limiting its lifespan is the cells obtaining radiation damage. By defining the limit of their radiation resistance, one can estimate the length of microorganisms surviving in the regolith of various depths.

After conducting several tests simulating Mars conditions, the researchers believe that hypothetical Mars ecosystems could be conserved in an anabiotic state in the surface layer of regolith for at least 1.3 to 2 million years, at a depth of two meters for no less than 3.3 million years, and at a depth of five meters for at least 20 million years.

 “We have studied the joint impact of a number of physical factors [gamma radiation, low pressure, low temperature] on the microbial communities within ancient Arctic permafrost,” Vladimir Cheptsov, a post-graduate student at Lomonosov MSU, said in a statement. “We also studied a unique nature-made object—the ancient permafrost which has not melted for about two million years.

“In a nutshell, we have conducted a simulation experiment that well covered the conditions of cryoconservation in Martian regolith,” he added. “It is also important that in this paper we studied the effect of high doses [100 kGy] of gamma radiation on prokaryotes' vitality, while in previous studies no living prokaryotes were ever found after doses higher than 80 kGy.”

The researchers simulated the factors influencing microorganisms and used an original constant climate chamber that allows them to maintain low temperature and pressure during gamma-irradiation. They also used natural microbial communities as a model object but not pure cultures of microorganisms.

After irradiation, the total count of prokaryotic cells and the number of metabolically active bacterial cells remained at the control level, while the number of cultured bacteria decreased ten times and the number of metabolically active cells of archaea decreased threefold.

The researchers believe the decrease in the cultured bacteria numbers was likely caused by a change in their physiological state and not by death.

The scientists found a fairly high biodiversity of bacteria in the exposed sample of permafrost, but the microbial community structure underwent significant changes after irradiation where the actinobacteria populations of the genus Arthrobacter became predominant in the bacterial communities following the simulation.

Mars has an average temperature of -63 degrees Celsius but temperatures can reach as low as -145 degrees Celsius in polar areas. On Mars there is pressure lower 100-to-1000 times than on the Earth, strong ultraviolet and ionizing radiation.