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.