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 can reach 145°C below zero. The pressure on the red planet is between a hundred and a thousand times less than on Earth, and its surface constantly receives a lethal bath of ultraviolet and ionizing radiation.
Terrestrial plants and animals could not thrive in this 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 the hydrothermal vents of the ocean floor and withstands temperatures of up to 120 degrees, or of the cyanobacteria Chroococcidiopsis, which supports the extreme dryness of the Atacama Desert in Chile. Since then, different teams of astrobiologists have been investigating 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, Moscow, has studied the resistance of some microorganisms to gamma radiation at very low temperatures, conditions similar to those prevailing on the Martian surface.
To determine this, they have observed how the microbial communities present in the sedimentary rocks of permafrost, the frozen firm layer characteristic 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 remained stable for two million years?
The aforementioned 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 the cells.
In this sense, the ideal would be to define the limit of their resistance to the aforementioned radiation, which would allow, in turn, estimating the survival capacity of the hypothetical microbes that lived in the subsoil of the red planet, at different depths.
The experts simulated that environment in a special chamber that allowed maintaining the pressure and constant temperatures while they bombarded it with radiation. In it they introduced communities of prokaryotes – unicellular organisms without a nucleus – similar to those found in nature, not obtained in the laboratory.
These showed a great resistance: after the irradiation, the total count of prokaryotic cells and those that maintained metabolic activity remained at the control levels. On the contrary, the number of other microorganisms, such as archaea or bacteria, decreased significantly, although, among the latter, those of the genus Arthrobacter were particularly resistant. These can occur at very low temperatures, such as in glaciers or abyssal pits, 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 anabotic state – without apparent life, but that could be revived if conditions improve – in a superficial layer of it, protected from ultraviolet rays, between 1.3 and 2 million years, two meters deep, it would be no less than 3.3 million years, and five meters underground, 20 million years or more. These same data could be applied to other bodies of the solar system, “Vladimir S. Cheptsov, one of the authors of the work, said in a statement.
Cheptsov and his colleagues have shown for the first time that prokaryotes can survive exposure greater than 80 kilograms – a unit that measures the absorbed dose from ionizing radiation – indicating that the resistance to this phenomenon of some microorganisms may have been underestimated…