  A new GEANT4 particle transport model -- the Atmospheric Radiation
Interaction Simulator (AtRIS, Banjac et al. 2018a. J. Geophys. Res.) -- has
been recently developed in order to model the interaction of radiation with
planets. The upcoming instrumentational advancements in the exoplanetary
science, in particular transit spectroscopy capabilities of missions like JWST
and E-ELT, have motivated the development of a particle transport code with a
focus on providing the necessary flexibility in planet specification
(atmosphere and soil geometry and composition, tidal locking, oceans, clouds,
etc.) for the modeling of radiation environment for exoplanets. Since there are
no factors limiting the applicability of AtRIS to Mars and Venus, AtRIS' unique
flexibility opens possibilities for new studies. Following the successful
validation against Earth measurements Banjac et al. 2018, J. Geophys. Res.,
this work applies AtRIS with a specific implementation of the Martian
atmospheric and regolith structure to model the radiation environment at Mars.
We benchmark these first modeling results based on different GEANT4 physics
lists with the energetic particle spectra recently measured by the Radiation
Assessment Detector (RAD) on the surface of Mars. The good agreement between
AtRIS and the actual measurement provides one of the first and sound
validations of AtRIS and the preferred physics list which could be recommended
for predicting the radiation field of other conceivable (exo)planets with an
atmospheric environment similar to Mars.
