Ion Acceleration and Outflow from Mars and Venus: An Overview

Abstract

Solar wind forcing of Mars and Venus results in outflow and escape of ionospheric ions. Observations show that the replenishment of ionospheric ions starts in the dayside at low altitudes (≈300-800 km), ions moving at a low velocity (5-10 km/s) in the direction of the external/ magnetosheath flow. At high altitudes, in the inner magnetosheath and in the central tail, ions may be accelerated up to keV energies. However, the dominating energization and outflow process, applicable for the inner magnetosphere of Mars and Venus, leads to outflow at energies ≈5-20 eV. The aim of this overview is to analyze ion acceleration processes associated with the outflow and escape of ionospheric ions from Mars and Venus. Qualitatively, ion acceleration may be divided in two categories: (a) Modest ion acceleration, leading to bulk outflow and/or return flow (circulation).