Radiation Transport Through the Martian Atmosphere as a Function of the Zenith Angle

Abstract

The topographic influence of the radiation environment on the Martian surface radiation is crucial for future human exploration. Topographic maps help assess radiation flux variations, aiding in hazard evaluation. Creating a global radiation map requires accounting for seasonally varying atmospheric density, heliospheric modulation, and topography. Here, we use a radiation model to derive the flux of secondary downward particles generated by the interaction of primary protons with the Martian atmosphere. Our model examines two key factors: (a) the dependence of atmospheric column depth on the zenith angle, affecting radiation directionality as horizon-arriving particles traverse more atmosphere than vertical ones and (b) atmospheric conditions at surface heights in Gale Crater, crucial for developing radiation dose maps that incorporate topographic effects. Our model is validated against Radiation Assessment Detector measurements and benchmarked with existing models. We construct response matrices representing the ratio of secondary particles at the Martian surface to primary inputs across zenith angles, assessing atmospheric effects. We combine these matrices with the incident spectrum to compute secondary particle fluxes from all zenith angles for Galactic Cosmic Rays and Solar Energetic Particles. These fluxes will be integrated into a topographic map of Mars in a follow-up study, providing a detailed representation of surface radiation levels across different terrains. This approach aids mission planners in identifying safe landing sites for astronauts.