We Now Know Exactly How Much Radiation Astronauts Will Face on the Moon

 In Environment

We final­ly know what kind of radi­a­tion envi­ron­ment future moon­walk­ers will be step­ping into.

Astronauts hopping about on the lunar surface will soak up about 60 microsiev­erts of radi­a­tion per hour, a new study reports. That’s 5 to 10 times higher than the rate expe­ri­enced on a trans-Atlantic pas­sen­ger flight and about 200 times what we get on Earth’s sur­face, study team mem­bers said.

“In other words, a long-term stay on the moon will expose astro­nauts’ bodies to high doses of radi­a­tion,” co-author Thomas Berger, a radi­a­tion physi­cist at the German Aerospace Center’s Institute of Aerospace Medicine in Cologne, said in a statement

Those num­bers are indeed high — but likely not high enough to impede crewed lunar explo­ration, as we shall see. 

Related: The space radiation threat to astronauts explained (infographic)

A pioneering result from a pioneering lander

Scientists have long known that radi­a­tion levels are rel­a­tive­ly high on the moon, which does not have a thick atmos­phere or a mag­net­ic field to pro­tect it. (Our Earth, for­tu­nate­ly, pos­sess­es both types of shield­ing.) But pre­cise num­bers have proven elu­sive. 

For exam­ple, the dosime­ters that NASA’s Apollo astronauts took to the moon from 1969 through 1972 record­ed the cumu­la­tive, total-mis­sion expo­sure, not a detailed break­down of radi­a­tion levels on the lunar sur­face. The new study gives us that detailed break­down.

The num­bers come cour­tesy of the Lunar Lander Neutron and Dosimetry instru­ment (LND), a German-built exper­i­ment that rides on China’s Chang'e 4 moon mission. Chang’e 4 made his­to­ry in January 2019 by per­form­ing the first-ever soft touch­down on the moon’s large­ly unex­plored far side. 

Chang’e 4 con­sists of a rover named Yutu-2 (“Jade Rabbit 2”) and a lander, both of which are still going strong. LND is part of the lan­der’s sci­en­tif­ic pay­load, and its par­tial­ly shield­ed posi­tion pro­vides “a good indi­ca­tion of the radi­a­tion inside a space­suit,” Berger said.

Charged par­ti­cles such as galactic cosmic rays (GCRs), which are accel­er­at­ed to tremen­dous speeds by far­away super­no­va explo­sions, con­tribute about 75% to the total lunar-sur­face dose rate of 60 microsiev­erts per hour, the LND data indi­cate. 

The GCR expo­sure rate on the moon is there­fore about 2.6 times higher than that expe­ri­enced by astro­nauts aboard the International Space Station, accord­ing to the new study, which was pub­lished online Friday (Sept. 25) in the jour­nal Science Advances. (The space sta­tion, while cir­cling above the vast major­i­ty of Earth’s atmos­phere, gains pro­tec­tion from our plan­et’s mag­net­ic field.)

Related: China releases huge batch of Chang'e 4 images from moon's far side

No roadblock for Artemis

NASA is work­ing to land astronauts on the moon in 2024 and estab­lish a sus­tain­able human pres­ence on and around Earth’s near­est neigh­bor by the end of the decade, via a program called Artemis. The lessons learned during Artemis will also help pave the way for the crewed leap to Mars, which NASA aims to achieve in the 2030s, agency offi­cials have said.

The newly report­ed num­bers won’t derail any grand Artemis plans, a read­ing of NASA's radiation-exposure rules sug­gests. Those rules stip­u­late that no astro­naut receive a career radi­a­tion dose that boosts the risk of life­time cancer mor­tal­i­ty by more than 3%. The total equiv­a­lent dose that poses this risk depends on the astro­naut’s gender and age at the start of radi­a­tion expo­sure, among other fac­tors.

Women and space­fly­ers who start young are at greater risk. For exam­ple, a female astro­naut who begins her space­flight career at the tender age of 25 has a career expo­sure limit of 1 mil­lion microsiev­erts, where­as the cap is four times that for a man who starts flying at age 55.

But at 60 microsiev­erts per hour, that 25-year-old female astro­naut could spend a total of nearly 700 Earth days explor­ing the lunar sur­face before vio­lat­ing her life­time expo­sure limit (though this cal­cu­la­tion does­n’t take into account her time in tran­sit to and from the moon). 

And the GCR num­bers mea­sured by LND are likely on the high side for any expo­sure that moon­walk­ers would expe­ri­ence, the study authors said. That’s because the data were gath­ered during an inac­tive stretch of the sun's 11-year activity cycle, when rel­a­tive­ly more GCRs were able to zoom through the helios­phere, the bubble of charged par­ti­cles and mag­net­ic fields that the sun blows around itself. 

All of this does­n’t mean that Artemis astro­nauts will ship off to the moon for two-year stints, how­ev­er; NASA will doubt­less want to stretch space­fly­ers’ radi­a­tion expo­sure out over time for safe­ty’s sake. Agency astro­nauts who fly aboard the space sta­tion, for exam­ple, cannot exceed 50,000 microsiev­erts of expo­sure per year.

And NASA will likely still take pains to min­i­mize the radi­a­tion risk expe­ri­enced by Artemis astro­nauts, espe­cial­ly those who spend a large chunk of time on and around the moon.

“On longer mis­sions to the moon, astro­nauts will have to pro­tect them­selves from it [radi­a­tion expo­sure] — by cov­er­ing their habi­tat with a thick layer of lunar rock, for exam­ple,” study co-author Robert Wimmer-Schweingruber, of the Christian-Albrecht University in Kiel, Germany, said in the same state­ment.

“This could reduce the risk of cancer and other ill­ness­es caused by long peri­ods of time spent on the moon,” said Wimmer-Schweingruber, whose team built LND.

Such mea­sures would also help guard against spo­radic but poten­tial­ly dan­ger­ous sun out­bursts known as solar particle events (SPEs). LND didn’t pick up any SPEs during the stretch cov­ered by the new study, but future lunar explor­ers could well get hit by one.

Mike Wall is the author of “Out There” (Grand Central Publishing, 2018; illus­trat­ed by Karl Tate), a book about the search for alien life. Follow him on Twitter @michaeldwall. Follow us on Twitter @Spacedotcom or Facebook. 

Space.com source|articles

Recommended Posts

Start typing and press Enter to search