Space exploration comes with many risks, one of which is exposure to space radiation. Outside of the protective bubble that is Earth’s magnetic field, particles from the Sun and the rest of the galaxy are a serious danger to human health.
Reporting in Science Advances, researchers have just quantified what level of radiation astronauts on the Moon can expect to be exposed to – and it is a lot. The team estimates that the equivalent dose of radiation astronauts would experience daily is about 1.3 milliSievert (a unit measuring the radiation dose received from a radioactive source). That’s 2.6 times higher than astronauts and cosmonauts experience on the International Space Station (ISS).
“The radiation levels we measured on the Moon are about 200 times higher than on the surface of the Earth and 5 to 10 times higher than on a flight from New York to Frankfurt,” Robert Wimmer-Schweingruber, corresponding author of the study, said in a statement. “Because astronauts would be exposed to these radiation levels longer than passengers or pilots on transatlantic flights, this is a considerable exposure.”
This level of effective radiation in a day is difficult to picture (check out this excellent XKCD infographic for some more comparisons, ranging from eating a banana, to dental X-rays, to spending a couple of weeks at Fukushima), but it is higher than what the Environmental Protection Agency expects an average American to be exposed to in one year (1 milliSievert). Those specifically working with radiation are only allowed to be exposed to a maximum of 50 milliSievert in one year. An astronaut on the Moon would cross that threshold in 38 days and 12 hours.
The informative measurements come from the Lunar Lander Neutrons and Dosimetry experiment aboard China’s Chang’e 4 lander, which is stationed on the far side of the Moon. This experiment is not the first measurement of radiation on the Moon, but it is the first one to reach this level of precision.
This obviously brings up the question of safety for astronauts. Space radiation is a concern that is constantly being investigated, especially when it comes to planning long-duration missions in deep space such as a return to the Moon or the even longer journey to Mars. Having a habitat built into the lunar soil or covered by it will help with radiation shielding. However, based on some of the Apollo 17 measurements, radiation from neutrons may be higher in those settlements.
All in all, visiting the Moon shouldn’t be too risky but actually living permanently on it may in fact shorten life, so we're not there yet. However, the team stresses that the measurements were collected during a period of solar minimum, so these measurements should be considered an upper limit for galactic cosmic rays.