Quantifying radiation risks to the human brain in space

Space radiation is ubiquitous outside the protective bubble of Earth’s magnetic field. Whether the radiation is emitted from solar energetic particles or cosmic rays streaming through the galaxy, it can damage human cells enough to cause health problems, including acute radiation syndrome, cardiovascular disease, and even a higher incidence of various cancers. NASA’s Artemis mission aims to bring astronauts to the Moon and eventually have them stay for possibly months, far longer than the 80 hours combined that Apollo astronauts spent on the lunar surface.

To better understand the radiation that human explorers may face , Jingnan Guo, from the University of Science and Technology of China in Hefei, and her colleagues have now analyzed historical data of solar energetic particles and galactic cosmic rays. They find that the radiation doses that future astronauts would be exposed to on Mars may be relatively safe for their brains but that the doses they would be exposed to on the Moon may sometimes exceed NASA’s recommended safe level, particularly during extreme space-weather events.

For the analysis, Guo and her team first compiled the flux of galactic cosmic rays and solar energetic particles that reached the Moon and Mars roughly from the mid 20th century to around 2012. The flux data were then used as inputs in a series of models to track the high-energy particles through space, simulate their interactions with the lunar and Martian environments, and evaluate the radiation doses reaching an astronaut.

Although the Moon and Mars had similar radiation dose rates on a per-day basis, some 20% of the Moon’s 65 extreme space-weather events over the past half century were above NASA’s recommended safe radiation limit of 500 milligrays, which is equivalent to about 33 000 dental x-ray scans. Mars, in contrast, had no such events exceeding that safe level, partially because of its radiation-blocking atmosphere.

The good news is that just a little bit of aluminum shielding is effective, according to model results. With a thickness of 2 cm, it lowered the brains’ radiation exposure to below the recommended safe level. (Y. Li et al., Space Weather 21, e2023SW003470, 2023 .)