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We finally know what kind of radiation environment future moonwalkers will enter.
Astronauts jumping on the lunar surface It will absorb about 60 microsieverts of radiation per hour, a new study reports. That’s 5 to 10 times higher than the rate experienced on a transatlantic passenger flight and roughly 200 times what we get on Earth’s surface, the study team members said.
“In other words, an extended stay in Moon it will expose the bodies of astronauts to high doses of radiation, “said co-author Thomas Berger, a radiation physicist at the Institute for Aerospace Medicine at the German Aerospace Center in Cologne, said in a statement.
Those numbers are really high, but probably not high enough to prevent manned lunar exploration, as we will see.
Related: Space Radiation Threat Explained to Astronauts (Infographic)
A pioneering result of 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, has both types of armor.) But the precise numbers have proven elusive.
For example, NASA dosimeters Apollo astronauts flew to the moon from 1969 to 1972 recorded the total cumulative exposure of the mission, not a detailed breakdown of radiation levels on the lunar surface. The new study gives us that detailed breakdown.
The numbers are courtesy of the Lunar Lander (LND) neutron and dosimetry instrument, a German-built experiment set up in China. Mission to the Moon Chang’e 4. Chang’e 4 made history in January 2019 by making the first soft landing on the far, largely unexplored side of the moon.
Chang’e 4 consists of a rover named Yutu-2 (“Jade Rabbit 2”) and a lander, both of which are still working hard. The LND is part of the lander’s scientific payload and its partially shielded position provides “a good indication of radiation inside a spacesuit,” Berger said.
Particles charged as galactic cosmic rays (GCR), which are accelerated to tremendous speeds by distant supernova explosions, contribute about 75% of the lunar surface’s total dose rate of 60 microsieverts per hour, the LND data indicates.
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 (September 25) in the journal Science Advances. (The space station, while circling over the vast majority of Earth’s atmosphere, gains protection from our planet’s magnetic field.)
Related: China publishes a large batch of images of Chang’e 4 from the other side of the moon
There are no obstacles for Artemis
NASA is working to landing astronauts on the moon in 2024 and establish a sustainable human presence in and around the Earth’s closest neighbor by the end of the decade, through a program called Artemis. The lessons learned during Artemis will also help pave the way for the crewed jump to Mars, which NASA aims to accomplish in the 2030s, agency officials said.
The newly reported numbers won’t derail any great Artemis plan, a reading of NASA Radiation Exposure Rules suggests. Those rules stipulate that no astronaut will receive a professional radiation dose that increases lifetime cancer mortality risk by more than 3%. The total equivalent dose posed by this risk depends on the sex and age of the astronaut at the onset of radiation exposure, among other factors.
Women and space travelers who start young are at higher risk. For example, an astronaut who begins her spaceflight career at the tender age of 25 has an occupational exposure limit of 1 million microsieverts, while the limit is four times higher than that of a man who begins flying at 55 years.
But at 60 microsieverts per hour, that 25-year-old astronaut could spend a total of nearly 700 Earth days exploring the lunar surface before violating her lifetime exposure limit (although this calculation does not account for her time in transit to and from 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. This is because the data was collected during an idle period 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 it.
However, all this does not mean that the Artemis astronauts will embark on the moon for periods of two years; NASA will certainly want to lengthen the radiation exposure of space flyers over time for safety reasons. The agency’s astronauts flying aboard the space station, for example, cannot exceed 50,000 microsieverts of exposure per year.
And NASA will likely still strive to minimize the radiation risk experienced by Artemis astronauts, especially those who spend a great deal of time on and around the moon.
“On longer missions to the moon, astronauts will need to protect themselves from it [radiation exposure] – covering their habitat with a thick layer of lunar rock, for example, “study co-author Robert Wimmer-Schweingruber of Christian-Albrecht University in Kiel, Germany, said in the same statement.
“This could reduce the risk of cancer and other diseases caused by long periods of time on the moon,” said Wimmer-Schweingruber, whose team built LND.
Such measures would also help protect against sporadic but potentially dangerous sunbursts known as solar particle events (SPEs). LND did not detect any SPE during the stretch covered by the new study, but future lunar explorers could be 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 extraterrestrial life. Follow him on Twitter @michaeldwall. Follow us on Twitter @Spacedotcom or Facebook.
