Influence of Mars Topography on Neutral Surface Radiation: Modeling and MSL/RAD Observations

Abstract Since landing in 2012, the Radiation Assessment Detector (RAD) onboard the Mars science laboratory (MSL) Curiosity rover has encountered different local landscapes, which have induced variations in the local surface environment. The aim of this study is to include realistic and site‐specific local topography for any position in a radiation transport model, and to validate this modeling strategy by comparison with MSL/RAD results. We present a method that integrates complex planetary surface models into neutron transport simulations to assess how surface heterogeneities influence secondary neutron environments—combining flexible terrain representation with radiation transport modeling. By modeling the topography of the main sites traversed by the rover, we show and quantify the dependence of downward neutron intensity on topography, in particular on the blocking zenith angle, across the different energy ranges: thermal, epithermal, fast neutrons. Using a method involving the visible surface from an observation point, we reconstruct the additional albedo neutron environment created by the terrain as seen by MSL/RAD, using the Atmospheric RAdiation Model for Ionizing spectra on martian Surface (ARAMIS). In particular, we show that the terrain‐generated thermal neutron spectrum increases with greater topographic relief, while the flux of high‐energy neutrons (>1 MeV) decreases.