Radiation on Moon nearly 200 times higher than Earth, long-term exposure can cause health problems, says study
Human exploration of the Moon is associated with substantial risks to astronauts from space radiation. According to experts, while several nations have publicized plans for future crewed missions to the Moon, astronauts would have to contend with many potentially harmful radiation sources, including galactic cosmic rays, sporadic solar particle events (when particles emitted by the Sun become accelerated), and neutrons and gamma rays from interactions between space radiation and the lunar soil.
Scientists have now analyzed how much radiation an astronaut may be exposed to on the lunar surface and it suggests that the daily radiation exposure on the Moon is about 2.6 times higher than onboard the International Space Station (ISS). The measurements were taken by the Chinese lunar lander Chang'e-4, which landed on the far side of the moon on January 3, 2019.
According to researchers, the radiation levels measured on the Moon are about 200 times higher than on the surface of the Earth. The measurements show an equivalent dose rate of about 60 microsieverts per hour. In comparison, on a long-haul flight from Frankfurt to New York, it is about 5 to 10 times lower, and on the ground, it implies 200 times lower.
Since astronauts would be on the moon for much longer than passengers flying to New York and back, this represents considerable exposure for humans, they warn. The findings have been published in Science Advances.
"This is the first time that radiation was measured on the surface of the Moon. Radiation levels are approximate as expected, although we see a higher dose from neutral particles than expected. We are still investigating possible causes of this. The total dose rate is about 5-10 times higher than what one receives on a transatlantic flight. Astronauts would also be exposed to this radiation for much longer than the duration of a transatlantic flight," corresponding author Dr Robert F Wimmer-Schweingruber, Institute for Experimental and Applied Physics of the Christian-Albrechts-University, Kiel, Germany, tells MEA WorldWide (MEAWW).
He is also affiliated with the National Space Science Center, Chinese Academy of Sciences, Beijing.
Dr Wimmer-Schweingruber emphasizes that the implications of the study's findings for future missions to the Moon depend on the mission itself. "If it is a short mission of a few days, our measurements simply help to predict the radiation levels which astronauts will see during their mission. If one considers a habitat on the surface of the Moon which astronauts will live in for prolonged periods of time, then our measurements show that it should be covered by about 80 cm of lunar soil to absorb most of the surface radiation. So the main implication for future missions is that we now have measurements to pin down the predictions which are based on simulations. This means that we now have better predictions for the surface radiation on the moon," he explains.
The analysis
The team says that while the Moon is the next stepping stone for human space exploration, and many countries plan to send astronauts there again, long-term exposure to galactic cosmic rays is known to cause health problems, including cataracts, cancer and degenerative diseases of the central nervous system or other organ systems. Moreover, exposure to solar particle events may cause more immediate damage, they add.
Accordingly, the investigators used data from China's 2019 Chang'e 4 lander mission to determine the amount of radiation that humans would be exposed to on the lunar surface in future missions to the Moon. The Lunar Lander Neutrons and Dosimetry (LND) experiment aboard the lander made the measurements of the radiation exposure to both charged and neutral particles on the lunar surface. The LND was developed and built at Kiel University, on behalf of the Space Administration at the German Aerospace Center (DLR).
The measurements taken by the LND allowed the calculation of the so-called "equivalent dose", which is important to estimate the biological effects of space radiation on humans. "The radiation exposure we have measured is a good benchmark for the radiation within an astronaut suit," writes co-author Thomas Berger, German Aerospace Center.
The device and lander were scheduled to take measurements for at least a year, and have now already exceeded this goal, according to scientists. The data from the device and the lander is transmitted back to Earth via relay satellite Queqiao, which is located behind the Moon. Based on their analysis, the team reports an average daily radiation dose equivalent to 1,369 microsieverts per day – about 2.6 times higher than the International Space Station crew's daily dose.
"To determine daily radiation exposure on the Moon's surface, which was not reported during the Apollo missions, (the research team) performed calculations using data collected by a stack of 10 silicon solid-state detectors mounted in a compartment of the Chang'e 4 lander, dividing the absorbed dose by accumulated time to arrive at the daily dose rate. The researchers suggest that the contribution of galactic cosmic rays to this dose rate was likely at its peak since the Sun was (and still is, currently) at a solar minimum, in which its magnetic field provides the least protection from these rays at any time during the 11-year solar cycle," the findings state.
Wimmer-Schweingruber recommends that astronauts staying on the surface of the Moon for a prolonged period of time should make use of a radiation shelter constructed from lunar soils. "We humans are not really made to withstand space radiation. However, astronauts can and should shield themselves as far as possible during longer stays on the moon, for example, by covering their habitat with a thick layer of lunar soil," says Wimmer-Schweingruber. Co-author Christine Hellweg from the German Aerospace Center, adds: "During long-term stays on the moon, the astronauts' risk of getting cancer and other diseases could thus be reduced."