Colonizing Mars is a herculean human and logistical undertaking, which will require efforts from humanity that it has never before made. Our red neighbor, if we really wish to set foot there one day, will impose on us immense constraints, which are, for the most part, still unresolved. Vessels adapted for travel and landing, energy autonomy, dust storms, synchronization of communications, absence of magnetosphere… The list is as long as an arm and it would be pointless to draw it up here, as each theme deserves more attention.
The most important issue obviously being the safety of the first colonists (Google is working on this), they will have to be protected from radiation, which constantly bombards Mars. Today, no existing combination could provide sufficient protection, while annual exposure on Mars is estimated at 400 mSv, or 60 times the terrestrial threshold. Several solutions have already been imagined in the past (underground colonies, suits lined with high density polyethylene, protection by drinking water, etc.), but we had never thought of turning to a living organism to use as a biological shield.
This organism is a mold called Cladosporium sphaerospermumwhich developed on Earth in one of the most hostile environments in our fold: reactor no. 4 of the Chernobyl power plant. According to work shared in several journals such as Mycological Research et Current Opinion in Microbiologythis mushroom uses melanin (a natural pigment that gives color to our body) to convert ionizing radiation into energy, through a process called radiosynthesis. An ideal candidate which could therefore serve us to erect organic barriers which would block radioactive particles while multiplying autonomously.
A mushroom with “radiant” properties
Cladosporium sphaerospermum is not a mushroom like any other: where any other form of life would wither away, it thrives and feasts. Discovered at the end of the 1990s on the internal walls of Chernobyl reactor no. 4, it is in reality attracted to radiation and demonstrates very high resilience.
Like plants that harness chlorophyll to convert solar photons, this mold uses its high concentration of melanin to capture gamma radiation energy and transform it into chemical energy. This is called radiosynthesis: a diversion of extreme environmental stress into an evolutionary advantage, allowing it to exploit energy sources prohibited to the rest of the living kingdom.
Several studies have even shown that it can grow and flourish towards sources where radioactive radiation is the most intense. Once in contact with fragments of radioactive graphite (nuclear fuel residue), it encompasses them and uses its enzymes to dissolve and break down these particles.
The future ally of space conquest?
It has already been tested on board the International Space Station (ISS); During a 30-day experiment, researchers grew strains on a nutrient medium while measuring the flow of radiation through the colony. The results revealed that the mold exhibited growth “ faster than normal » compared to the control samples remaining on Earth. A real tough one, given that the ISS already bathes in a radiative environment much more intense than our planet.
This same study demonstrated that a layer of only 2 millimeters thick of this fungus already made it possible to block around 2% of incident cosmic radiation. By extrapolating this data, we estimate that a biological shield of around twenty centimeters (mixed with Martian regolith) could be sufficient to effectively protect a potential Martian base from radiation.
The so-called shields passive (like those with lead), which could also be used on habitats or in suits, have two big disadvantages: they have to be transported, and they erode over time. Conversely, if colonies of
Cladosporium sphaerospermum are carried there, they could reproduce and self-repair, since they exploit the same radiation that they intercept to densify and strengthen the protection of astronauts.
Who would have thought that the worst nuclear disaster in history would one day give us one of the keys to becoming a multiplanetary species ? However, let’s not get carried away: if this mold has potential, nothing is yet engraved in the regolith ; the researchers point out that all work concerning it is, for the moment, experimental. Several gray areas remain, in particular on its capacity to endure the extreme temperatures of Mars (which can drop to -125°C) or on the risks of biological contamination, which could pollute Mars forever. Last point: we still do not know what are the long-term effects of prolonged exposure to the spores of this funguswho travel by air. If the slightest respiratory danger is suspected (this is the case for many molds unfortunately), then Cladosporium sphaerospermum will be able to say goodbye to his status as a future star of Martian conquest.
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