Mars appears as a red-orange orb with darker spots and white ice caps visible at both poles.
There are many goals of the Mars mission, although one goal is to collect some samples and bring them back to Earth. But what if there really is life on Mars? What steps can be taken to protect our planet from extraterrestrial sources of microbial contamination?
Additionally, it is important not to confuse Earth life with indigenous life returned from Mars.
These considerations led to a consideration of how optimally to consider the effects of desiccation and freezing on the survivability of microbial ionizing radiation on Mars. Many types of bacteria and fungi possess various strategies that allow them to survive desiccation in the form of spores or when simply desiccated as germ cells.
With the research, the goal was to better understand the impact of the Martian surface on microbial dormancy and survivability. To do this, scientists reproduced the conditions on Mars. This involved testing the effect of drying and freezing on ionizing radiation survival using six model microorganisms.
The organisms were: Plant cells of two bacteria (Deinococcus radiodurans, Escherichia coli), a yeast strain (Saccharomyces cerevisiae), and plant cells and endospores of the three Bacillus species of bacteria (B. subtilis, B. megaterium, B. thuringiensis). The scientists found that drying and freezing increased the survival of plant microorganisms from radiation. Here there is a strong relationship between the processes of desiccation, freezing and survival from radiation.
For example, research has found that dried and frozen cells of the bacterium Deinococcus radiodurans can survive high levels of ionizing radiation (this organism has by far the highest levels of radioresistance). This is at a level equivalent to hundreds of millions of years of background radiation on Mars. This includes levels up to 140 kGy for organisms in the lyophilized state. A “gray” is defined as the absorption of one joule of radiant energy per kilogram of matter. Sterilization is typically achieved at 15-25 kGy.
From this it can be concluded that if there was ever life on Mars, then organisms such as D. radiodurans Cells could survive 280 million years in the icy subsurface of Mars. Furthermore, their macromolecules would survive much, much longer.
The implications of these findings are that if life ever did evolve on Mars, there is a good chance that it will be revealed in future missions.
On the other hand, since some microorganisms can survive on the spacecraft and in the spacecraft environment, there is a very real possibility that Earth microbes will contaminate specific landing sites on Mars.
It is also possible that some microorganisms introduced from Earth to Mars (Mars survivors) could also be carried back to Earth. This will present a complexity in deciphering whether these organisms were originally from Earth or were originally Martian.
The results of the study have been published in the journal Astrobiology. The research is titled “Effects of Desiccation and Freezing on Microbial Ionizing Radiation Survival: Considerations for Sample Return to Mars.”
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