The Impact of Space Radiation on Brains of Future Martian and Lunar Explorers

Astronauts will be facing many risks when they are away from Earth's environment, among which radiation is one of the most vital and troublesome issues. Space radiation exposure from energetic particles of Solar Energetic Particles (SEPs) and Galactic Cosmic Rays (GCRs) can adversely impact the Central Nervous System (CNS) by inducing acute (i.e., mission critical) and chronic (i.e., post-mission) effects, respectively. Recently, Brain Response Functions (BRFs) based on a realistic brain structure have been developed to model cosmic-ray induced dose in the brain (Khaksarighiri et al., 2020, ). In this study, to quantify the radiation induced dose and evaluate the radiation risk to the CNS of the astronauts on the surface of Mars and Moon and in deep space, we use GCR/SEP spectral models together with Mars/Moon radiation transport codes to obtain the radiation field to which astronauts are exposed, and derive the absorbed dose in the brain with BRFs. Our calculations show that GCR induced absorbed dose per month in the brain does not reach the 30-day limit for CNS (500 mGy) as defined by NASA on either Martian or lunar surface. Based on the spectra and frequency of historical extreme SEP events recorded at Earth as ground-level enhancement events over past five solar cycles, our results suggest that the CNS of astronauts will be generally "safe" on the Martian surface, but those on the lunar surface or in deep space may face radiation risks in their CNS if not well shielded during such extreme events. Among various concerns for the health of future astronauts exploring the Moon and Mars, space radiation-induced health risks cause one of the most urgent and vital problems for future missions. The astronauts will be exposed to the Galactic Cosmic Rays (GCRs) as background radiation and sporadic while potentially more hazardous Solar Energetic Particles (SEPs), which would leave energy and deposit dose in the human body of astronauts who may consequently suffer from a series of acute or post-mission health issues. Here we study the dose deposited in the brain when exposed in deep space or the lunar/Martian radiation environment induced by the above GCR and SEP radiation sources. In particular, the surface radiation environment of the Moon or Mars could be different from that in deep space due to particle interactions with the planetary atmosphere and/or regolith, which can be derived from the Monte-Carlo simulations. Finally, we calculate the resulting dose in a model with a realistic head structure. Our calculations suggest that during extreme SEP events, astronauts' CNS may face radiation risks in deep space or on the lunar surface if not well shielded, but it is generally "safe" for their brains on the Martian surface. We model the dose in the head exposed to the Martian and lunar surface radiation environmentWe analyze the "brain" dose correlation between the Martian and lunar resultsWe evaluate the space radiation risks for "brains" of future Martian and lunar explorers