MICROPHYSICS OF THE VENUSIAN AND MARTIAN MANTLES

The planetary ionospheres around the nonmagnetic planets Mars and Venu s are directly exposed to the shocked solar wind. An interaction betwe en the solar wind protons and the ionospheric oxygen takes place in a narrow turbulent region referred to as the plasma mantle. In this lett er the microphysics of the dayside mantle is investigated numerically using a one-dimensional hybrid code that retains the inertia of the el ectron species. It is shown that lower hybrid waves propagating perpen dicular to the magnetic field are destabilized. Wave saturation is cau sed by electrostatic trapping of the proton species, and the saturated amplitudes are shown to be in reasonable agreement with Pioneer-Venus observations. Oxygen pick-up and acceleration is found to be dominate d by wave effects, resulting in significant ion heating, consistent wi th Phobos observations.