Finally, we know what kind of radiation environment future moonwalkers will step into.
Astronauts jumps around on the surface of the moon will absorb about 60 microsieverts of radiation per hour, a new study reports. That’s 5 to 10 times higher than the speed experienced on a transatlantic passenger flight, and about 200 times what we get on the earth’s surface, study members said.
“In other words, a long stay the moon will expose astronauts’ bodies to high doses of radiation, “co-author Thomas Berger, a radiation physicist at the German Space Center̵
These numbers are actually high – but probably not high enough to hinder manned lunar research, as we shall see.
Related: Space radiation threat to astronauts explained (infographic)
A groundbreaking result from a groundbreaking 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. (Fortunately, our earth has both types of shielding.) But accurate numbers have evaded.
For example, the dosimeters that NASA has Apollo astronauts trains to the moon from 1969 to 1972 recorded the cumulative exposure in total mission, not a detailed breakdown of radiation levels on the moon’s surface. The new study gives us the detailed breakdown.
The figures come with permission for the Lunar Lander Neutron and Dosimetry instrument (LND), a German-built experiment running in China Chang’e 4 moon mission. Chang’e 4 made history in January 2019 by performing the first soft touchdown ever on the moon’s largely unexplored distant 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 enormous speeds by distant supernova explosions, contribute approx. 75% to the total dose on the lunar surface of 60 microsieverts per hour, LND data show.
The GCR exposure rate on the moon is therefore approx. 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, as it orbits the vast majority of the Earth’s atmosphere, is protected from the magnetic field of our planet.)
Related: China releases a large number of Chang’e 4 images from the far side of the moon
No roadblock for Artemis
NASA is working on that land astronauts on the moon in 2024 and establish a sustainable human presence on and around the Earth’s nearest neighbor by the end of the decade via a program called Artemis. The learning from Artemis will also help pave the way for the occupied leap to Mars, which NASA aims to achieve in the 2030s, agency officials have said.
The recently reported figures will not track any major Artemis plans, a reading of NASA’s rules for radiation exposure suggests. These rules stipulate that no astronaut receives a career radiation dose that increases the risk of lifetime cancer mortality by more than 3%. The total equivalent dose that poses this risk depends, among other things, on the astronaut’s gender and age at the start of radiation exposure.
Women and space pilots starting young are at greater risk. For example, a female astronaut beginning her career in space at the age of 25 has a career exposure limit of 1 million microsievers, while the cap is four times as high for a man beginning to fly at the age of 55.
But at 60 microsieverts per hour, the 25-year-old female astronaut could spend a total of nearly 700 Earth days exploring the moon’s surface before exceeding her lifetime exposure limit (although this calculation does not 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 of any exposure that moonwalkers would experience, the study authors said. This is because the data was collected during an inactive stretch of the sun’s 11-year activity cycle, when relatively more GCRs could zoom through the heliosphere, the bubble of charged particles and magnetic fields that the sun blows around itself.
All this does not mean, however, that the Artemis astronauts send out to the moon for two years. NASA will no doubt want to extend the spacecraft’s radiation exposure beyond time for safety’s sake. For example, the agency’s astronauts flying aboard the space station cannot exceed the exposure of 50,000 microsievers per year.
And NASA will likely still hurt to minimize the radiation risk Artemis astronauts experience, especially those who spend much of their time on and around the moon.
“On longer missions to the moon, astronauts will have to protect themselves from it [radiation exposure] – by e.g. To cover their habitat with a thick layer of moonstone, “said co-author Robert Wimmer-Schweingruber of Christian-Albrecht University in Kiel, Germany, in the same statement.
“This can reduce the risk of cancer and other diseases caused by long periods of time on the moon,” said Wimmer-Schweingruber, whose team built the LND.
Such measures will also help protect against sporadic but potentially dangerous solar flares, known as events of solar particles (SPEs). LND did not pick up any SPEs during the stretch covered by the new study, but future lunar scientists could well be affected 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.