A Mushroom Shield Will Protect Astronauts From Radiation
American researchers have found that microscopic fungi Cladosporium sphaerospermum can be an anti-radiation shield. This property was confirmed during the experiment on the ISS: it turned out that a mushroom film less than two millimeters thick can reduce the radiation flow by almost two percent. According to calculations, to bring the Martian level of ionizing radiation to safe values, it will be enough to "shield" 21 centimeters thick. The results of the study are published in the bioRxiv Preprint service.
Once outside the Earth, a person is exposed to significant radiation exposure. For example, astronauts during their time on the ISS receive an average dose of 144 millisieverts, and for a member of the Martian expedition, this figure will be 400 millisieverts in just a year. On The earth's surface, radiation is much less intense: the average annual dose is 6.3 millisieverts.
Although the impact of cosmic radiation on health remains poorly understood, experts do not doubt that it is necessary to protect yourself from it. However, creating mechanical protective shields requires a lot of materials, while the amount of payload that can be taken with you to space is limited.
The original solution to this problem was proposed by Graham K. Shunk and Xavier R. Gomez. The first of them is now studying at a school in North Carolina, and the second went to a local University. They noticed that some living organisms successfully cope with the effects of radiation. Some species of fungi have even learned to absorb ionizing gamma radiation using the pigment melanin and use it to produce their biomass in the process of radiosynthesis. Among them — Cladosporium sphaerospermum, some strains of which survive even in the destroyed reactor of the Chernobyl nuclear power plant.
Schank and Gomez suggested that a layer of such mushrooms could be an excellent anti-radiation shield for space travelers and Martian colonists. One of its main advantages is that mushrooms can be grown locally from a sample weighing several grams, rather than carrying a lot of consumables such as aluminum or stainless steel.
This idea allowed researchers to win a space innovation competition, and in December 2018, a colony of C. sphaerospermum went to the ISS. For 30 days, Geiger counters recorded the flow of ionizing radiation through two halves of a Petri dish, one of which was populated with mushrooms, and the second was a control one (it was filled with agar).
The colony of C. sphaerospermum perfectly endured freezing during the flight to orbit and quickly began to grow on the ISS. As soon as the mushroom layer becomes thicker, the radiation flow through it has decreased. During the first 24 hours, the radiation level under the "mushroom" half of the Petri dish was 0.5 percent lower than under the control. However, by the end of the experiment, the difference had increased to about two percent. The mushrooms only blocked one side of the Geiger counter, so if they surrounded it completely, this figure could be doubled.
Although the decrease in radiation flux by several percents may seem insignificant, it should be noted that this result was achieved due to a thin mushroom film with a thickness of 1.7 mm. According to calculations, to reduce the radiation flow on Mars to earth levels, a mushroom shield 21 centimeters thick will be required. According to the authors, to create it, it is best to mix mushrooms with Martian soil and periodically pour meltwater from the polar caps. Another option is to create a composite material from local soil in combination with melanin extracted from fungi pigments. For protection from radiation, a nine-centimeter layer of such a composite will be enough.
Korean scientists have discovered a way to protect mice from radiation sickness. They demonstrated that cerium dioxide nanoparticles with a surface layer of mixed manganese oxide increase the catalytic activity against reactive oxygen particles — one of the indirect mechanisms of radiation exposure to living organisms. In an experiment, they increased the survival rate of mice after a high dose of radiation to 67 percent.