Radiation risk models for Mars exploration

In space, astronauts are exposed to two sources of radiation: the primary cosmic radiation made up of galactic cosmic rays (GCR) characterized by high-energy protons and heavy energy (HZE) ions, which have a high charge (Z) and energy (E), and solar particle events (SPEs) comprised largely of low to medium energy protons. When the primary cosmic radiation interacts with the atmosphere, the astronauts are exposed to secondary cosmic radiation, which includes neutrons and the recoil nuclei produced.The majority of missions involve astronauts aboard the International Space Station (ISS). However, the interest of space agencies around the world is shifting towards more distant destinations, with the main goals being a return to the Moon and the first human landing on Mars. Each of these imply the full assessment of a unique environment and require a deep understanding of the health risks to astronauts and the development of effective countermeasures to ensure the success and safety of these endeavours.The focus of this review is on the methodologies adopted by space agencies for risk estimation, and on simulations of possible exposure scenarios during missions to Mars.