Solar particle events and radiation exposure risks in Mars missions

Radiation hazard in near-Earth space, and in the inner solar system, is caused by a number of factors among which, besides the time of exposure to the radiation environment, the most significant are the orbital parameters of satellites, as well as the levels of solar and geomagnetic activities leading to radiation flux enhancement. The main components of the radiation environment, surrounding the Earth are: galactic cosmic rays, solar energetic particles and the radiation belts. Solar energetic radiation is subject to studies from the point of view of biological radiation impact. As case studies, effects of solar particle events recently measured on Mars and the Moon are assessed. Solar particle events have been observed by RAD (Radiation Assessment Detector) on the surface of Mars: recent peaks in the solar-activity cycle have caused relevant peaks in the radiation dose measurements, both on Mars and on the Selenic surfaces. After the RAD measurements during Curiosity's flight to Mars and on the surface of Mars, solar particle events are the big unknown in predicting the radiation exposure for a human mission to Mars. They are contributing an unknown but certainly significantly higher amount to the overall dose.