The Pivot Energy of Solar Energetic Particles Affecting the Martian Surface Radiation Environment

Space radiation is a major risk for humans, especially on long-duration missions to outer space, e.g., a manned mission to Mars. Galactic cosmic rays contribute a predictable radiation background; the main risk is due to the highly variable and currently unpredictable flux of solar energetic particles (SEPs). Such sporadic SEP events may induce acute health effects and are thus considered a critical mission risk for future human exploration of Mars. Therefore, it is of the utmost importance to study, model, and predict the surface radiation environment during such events. It is well known that the deep-space SEP differential energy spectrum at high energies is often given by a power law. We use a measurement-validated particle transport code to show that, for large SEP events with proton energy extending above ∼500 MeV with a power-law distribution, it is sufficient to measure the SEP flux at a pivot energy of ∼300 MeV above the Martian atmosphere to predict the dose rate on the Martian surface. In conjunction with a validation by in situ measurements from the Martian surface, this remarkable simplification and elegant quantification could enable instant predictions of the radiation environment on the surface of Mars upon the onset of large SEP events.