Astronauts take many risks in space, but exposing themselves to dangerous radiation is one of the biggest. On the International Space Station, astronauts are exposed to up to 160 millisieverts of radiation during a six-month mission, according to NASA, that's about 1,600 chest x-rays, and 26 times more than the average US citizen receives. Mars is even worse; an astronaut making an 18-month round trip to the red planet would be exposed to 1,000 millisieverts of radiation, or 10,000 chest x-rays' worth.

For protection, astronauts generally rely on radiation shields made of plastics or metals like aluminum and stainless steel. But these can be heavy and vulnerable to damage.

So in 2018, some high school students from Durham County, North Carolina proposed an unusual solution to this problem: Make a shield out of mold.

Specifically, they suggested cladosporium sphaerospermum, an organism that appears to feed on nuclear radiation the same way most plants feed on sunlight. The mold has thrived in Chernobyl's exclusion zone, the site of the 1986 nuclear meltdown, which is still one of the most radioactive places on Earth.

The students, led by Graham Shunk, now an incoming second-year student at the North Carolina School of Science and Mathematics, obtained samples of the mold species from a company in Minnesota. With the help of the research company Space Tango, they blasted them into outer space in December 2018.

On the International Space Station, astronauts put the mold samples into Petri dishes, leaving one side of each dish empty. Geiger counters then measured radiation levels beneath the dishes every 110 seconds for 30 days. The results showed that radiation levels decreased at the height of the mold's growth: The counters measured a 2.4% decrease in average radiation levels beneath the mold-covered sides.

Researchers grew Cladosporium sphaerospermum mold on the left sides of petri dishes on the International Space Station. Space Tango, Inc.

The preliminary findings from that experiment were uploaded to the research archive bioRxiv on July 17, but have not yet been peer-reviewed. Still, they suggest that the mold could act as a shield against radiation in space.

That's because the mold appears to absorb radiation and convert it into chemical energy in a process called radiosynthesis. It's similar to photosynthesis, the process most plants use to convert sunlight into energy.

Shunk and the other researchers suggested that if the mold were about 21 centimeters thick, it could provide humans adequate protection from radiation levels on Mars. The protection would be stronger if the mold surrounded an object entirely, they think, instead of just shielding one side as it did in the study.

The International Space Station orbits Earth. NASA

The mold has a big advantage over other types of radiation shields, the researchers also noted, since it can grow and replenish itself in space. That means a microscopic amount of C. sphaerospermum could be all that's needed at the start of a launch so it wouldn't add extra weight to a rocket. That could be a game-changer, since NASA estimates that launching something into space costs about $10,000 per pound.

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