NASA recently unveiled the plan for its Artemis program, a series of missions that would return astronauts to the moon.
A new study found how much radiation astronauts are exposed to on the lunar surface: a daily dose about 200 times as great as on Earth.
NASA wants to build a base on the moon, but the new data suggests it'd be safest to bury such a base under 2.5 feet of moon dirt to protect astronauts from radiation.
NASA wants to build a permanent base on the moon by the 2030s — a place astronauts could stay for extended visits at the lunar south pole.
But a new study found that any astronauts who go there would face levels of radiation nearly three times as high as what the astronauts on the space station deal with. Long-term exposure to enough of this cosmic radiation poses significant health risks, including cataracts, cancer, and diseases of the central nervous system.
The new research, published last week in the journal Science, calculated for the first time what a moonwalker's daily dose of radiation would be.
"If you think about people staying on the moon for extended periods of time — say, on a scientific research station for a year or two — then these levels start getting problematic," Robert Wimmer-Schweingruber, an author of the new study, told Business Insider.
The solution, he said, would be to build any lunar base beneath the moon's surface.
"Covering your habitat with sufficient amounts of lunar dirt should do the trick," Wimmer-Schweingruber said.
The first study to calculate radiation on the moon
Apollo astronauts carried radiation-measuring instruments on their missions in the 1960s and '70s, but those dosimeters could tell scientists only the total amount of radiation the astronauts were exposed to throughout their time in space, from blasting off to landing, not just on the moon.
Wimmer-Schweingruber's team was able to document daily radiation levels on the moon's surface by analyzing data collected by China's Chang'e 4 spacecraft, which landed in January 2019.
A tool aboard Chang'e 4 measured the total amount of radiation it had absorbed, then relayed that radiation data back to Earth via satellites. Then it was simple arithmetic: The researchers divided that total radiation dose by the amount of time the tool had collected data to calculate the daily total.
"The radiation exposure we have measured is a good benchmark for the radiation within an astronaut suit," Thomas Berger, another author of the study, said in a press release.
200 times the radiation we experience on Earth
Radiation is a catch-all term — Wimmer-Schweingruber described it simply as "energy being deposited into places in your body that it shouldn't be, to sometimes ill effect."
On Earth, that energy can come in the form of light and heat, which we can feel, as well as from sources like X-rays, which we can't. The planet's strong magnetic field and a thick atmosphere shield the surface from most cosmic radiation, which comes from galactic cosmic rays, solar particles speeding away from the sun, neutrons, and gamma rays.
When people fly on planes, they soar above part of that atmospheric shield, so the dose of radiation they're exposed to increases. Astronauts on the moon, meanwhile, face a daily radiation level five to 10 times as high as transatlantic fliers, since the moon doesn't have the shield that Earth does.
So an astronaut on the lunar surface would be exposed to 1,369 microsieverts of radiation per day, about 200 times the daily level on Earth.
"This is a considerable exposure," Wimmer-Schweingruber said.
That's why his team suggests burying lunar bases.
"Ideally you'd like to be under as much material as is equivalent to Earth's atmosphere," Wimmer-Schweingruber said, adding that "an optimal depth is 30 inches of lunar soil."
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