Could the planet Mars be easily contaminated by microorganisms from Earth?
To answer this question, a scientific team focused on tardigrades, tiny animals with exceptional resistance. Their incredible robustness makes them perfect candidates to assess the possibility of life on other planets and to measure the risks of potential contamination.
To reproduce Martian regolith, researchers used substitutes developed from data collected by robots like Curiosity. Two simulants were thus employed: the first representing the average soil of Mars, and the second a particular area of Gale Crater. These reproductions allow for the study of soil characteristics in the absence of real samples, based on chemical analyses performed on site.
Exposure to the two simulants led to a striking result: the tardigrades entered stasis, which is synonymous with extreme stress for these organisms, in only forty-eight hours on the first. The second simulant was barely better. This phenomenon highlighted the presence of an element in this artificial soil capable of actively slowing biological processes, indicating the existence of harmful compounds acting quickly on organisms.
After rinsing, the scientists noted a notable increase in the activity of the tardigrades. This improvement shows that the inhibiting agent is water-soluble, probably in the form of salts or other compounds, which could thus be easily eliminated.
Microscope images of active tardigrades in terrestrial sand (top row) and in a Martian regolith simulant (bottom row).
Credit: Corien Bakermans/Penn State This discovery has immediate consequences for planetary protection, whose goal is to prevent the contamination of extraterrestrial environments by terrestrial microbes. If Mars has natural defenses, the risks for future missions could be reduced. A more flexible exploration would then become conceivable, without threatening the integrity of hypothetical local ecosystems.
Moreover, learning to make Martian soil more accommodating is interesting in the longer term for potential human settlement projects. The cultivation of plants on Mars gains plausibility, with possible benefits for oxygen and food production, while maintaining a barrier against organisms from Earth.