A primitive equation, solar driven, thermospheric model is derived which has applications to the neutral gas components on Mars and Venus. The full effects of molecular viscosity and thermal conductivity are included, necessitating the development of a combined analytic and numerical solution technique. The model is applied to Venus in order to understand how thermospheric rotation, if present, would affect the dynamics. Results indicate that rotation periods of eight days or less should be observable. Application of the model to Mars indicates that the perturbation solar heating and the atmospheric response have primarily a diurnal component for which typical temperature and zonal wind maximum amplitudes are 20 K and 30 m/sec respectively. Because of uncertainty in the solar heating efficiency, calculations were made varying this parameter by an order of magnitude. The results imply that the response due to solar forcing alone is probably too small to account for observed concentrations of the minor constituents CO and O. An upper limit estimate is made of the upward propagation of wave energy from the lower atmosphere and the resulting response of the thermosphere.