THE MARTIAN THERMOSPHERE IONOSPHERE AT HIGH AND LOW SOLAR ACTIVITIES

We compare here models of the thermosphere/ionosphere of Mars at low and high solar activities, and we present heating rates and efficiencies due to the absorption of solar radiation in the 18 to 2000 Angstrom range. Using neutral model densities from the NCAR Mars Thermospheric General Circulation Model (MTGCM) of Bougher and co-workers, and solar fluxes from W. K. Tobiska, we have modeled the density profiles of 14 ions and 5 minor neutral species. We predict the variations in the ion densities with solar activity, and describe the sources and sinks of the ions. The major sources and sinks differ in some respects from those for the Venus ionosphere, and these differences are discussed as well. We find that the predicted total electron density profile computed using solar fluxes from Tobiska is somewhat different from that obtained using the fluxes of Hinteregger. One possible conclusion is that, at the time of Mariners 6 and 7, the soft x-ray fluxes were midway between those of the Tobiska and Hinteregger spectra.