Mars is extremely hostile to life, at least as we know it. The average temperature in our neighboring world is -63 ° C, although at night and in the polar regions it can reach 145 ° C below zero. The pressure on the red planet is between one hundred and one thousand times less than on Earth, and its surface is constantly being bathed in deadly ultraviolet and ionizing radiation.
Terrestrial plants and animals could not thrive in such an environment, but would any microorganism be capable of doing so? In the 80s, the first Extremophiles were discovered, microbes that manage to develop under conditions of salinity, temperature, pressure or dryness that, until then, were considered incompatible with life . This is the case, for example, of Pyrolobus fumarii , which lives near hydrothermal vents on the ocean floor and resists temperatures of up to 120 degrees, or of the cyanobacteria Chroococcidiopsis , which supports the extreme aridity of the Atacama desert, in Chile. Since then, different teams of astrobiologists have investigated whether some of them could survive on other planets and satellites in the solar system.
This information will be very useful when the next missions to explore these bodies are launched, among whose objectives will be the detection of life.
Now, a team of scientists from the Faculty of Soil Sciences of the MV Lomonosov State University, in Moscow, has studied the resistance of some microorganisms to gamma radiation at very low temperatures, conditions similar to those that prevail on the Martian surface. .
To determine this, they have observed how the microbial communities present in the sedimentary rocks of the permafrost, the characteristic frozen firm layer of Siberia and large areas of Alaska, Canada and Norway, where the pressure and temperature are very low, deal with radiation. which in some cases has been stable for two million years.
These rocks are considered a terrestrial analog of the Martian regolith, that is, the dust and deposits of materials that cover the ground. Those responsible for the trial believe that the possible Martian biosphere could survive in a kind of cryopreserved state , and that the main factor that prevents life from occurring on Mars is the damage that radiation causes to cells.
In this sense, the ideal would be to define the limit of its resistance to the aforementioned radiation, which would allow, in turn, to estimate the survival capacity of the hypothetical microbes that live in the subsoil of the red planet, at different depths.
Born survivors
The experts simulated this environment in a special chamber that kept the pressure and temperatures constant while bombarding it with radiation. In it they introduced communities of prokaryotes – unicellular organisms without a nucleus – similar to those that can be found in nature, not obtained in the laboratory.
These showed great endurance: after irradiation, the total count of prokaryotic cells and those that maintained metabolic activity remained at control levels. On the contrary, the number of other microorganisms, such as arcaea or bacteria, decreased notably, although, among the latter, those of the genus Arthrobacter were especially resistant. These can occur at very low temperatures, such as in glaciers or abyssal trenches, and withstand ultraviolet radiation.
“If we take into account the intensity of the radiation present in the Martian regolith, our data allow us to assume that a possible Martian ecosystem could be conserved in an anabiotic state – with no apparent life, but that it could revive if conditions improve – in a surface layer. of it, protected from ultraviolet rays, between 1.3 and 2 million years ; at two meters depth, it would make it no less than 3.3 million years; and at five meters underground, 20 million years or more. These same data could be applied to other bodies in the solar system, “says Vladimir S. Cheptsov, one of the authors of the work, in a statement.
Cheptsov and his colleagues have shown for the first time that prokaryotes can survive an exposure greater than 80 kilograys – a unit that measures the absorbed dose from ionizing radiation – indicating that the resistance to this phenomenon of some microorganisms may have been underestimated. .
Referencia: 100 kGy gamma-affected microbial communities within the ancient Arctic permafrost under simulated Martian conditions. Cheptsov, V.S., Vorobyova, E.A., Manucharova, N.A. et al. Extremophiles (2017) 21: 1057. https://doi.org/10.1007/s00792-017-0966-7
Image: NASA
