Plasma measurements in the Venus near wake

A study of the plasma measurements conducted with the Mariner 5, Venera 9 and 10, and the Pioneer Venus spacecraft in the Venus ionosheath and near wake is presented. The data available indicate that in the inner ionosheath, downstream from the terminator, the density and the velocity of the plasma are significantly smaller than those measured further outside. The slower particle fluxes detected near the ionopause also exhibit higher plasma temperatures and show a tendency to move towards the nightside hemisphere. The observation of high plasma temperatures in the inner ionosheath indicates that the interaction of the solar wind with the Venus ionospheric/exospheric material is dominated by dissipative phenomena, and that its entry into the wake is due to local thermal expansion processes.