Classic approaches in modeling planetary atmospheres, which are based on kinetic transport coefficients, have an upper limitation in altitude due to the transition from collisional to noncollisional regions; consequently, models developed until now have been constrained under the exobase. Furthermore, such models require hypotheses for diffusion coefficients, thermal conductivity, and viscosity in the case where several major species coexist in the medium. In order to solve the whole atmosphere from the ground to the heart of the exosphere, we have developed a new one-dimensional model based on a collisional approach. This was applied to Mars, using a 13-moment approximation in order to obtain profiles of the concentrations, velocities, temperatures, heat fluxes, and stress tensors versus altitude for each of the main species (CO2, N2, O2, CO, O, and H). The aim was to validate our mathematical approach and study the dominant physical processes versus altitude. The relevance of the approximations used in classic models was evaluated, and new phenomena that appear above the exobase are presented, all of which have important consequences on concentration, velocity, and temperature profiles. Finally, some modifications are proposed to classic approaches in order to incorporate such mechanisms, and perspectives of the model are presented concerning the interactions between the upper atmosphere and the space environment.