Effects of Magnetic Turbulence on the Dynamics of Pickup Ions in the Ionosheath of Mars

Abstract

We study some of the effects that magnetic turbulent fluctuations have on the dynamics of pickup O⁺ ions in the magnetic polar regions of the Mars ionosheath. In particular we study their effect on the bulk velocity profiles of ions as a function of altitude over the magnetic poles, in order to compare them with recent Mars Express data; that indicate that their average velocity is very low and essentially in the anti-sunward direction. We find that, while magnetic field fluctuations do give rise to deviations from simple E × B-drift gyromotion, even fluctuation amplitudes much greater than those of in situ measurements are not able to reproduce the vertical velocity profile of O⁺ ions. We conclude that other physical mechanisms, different from a pure charged particle dynamics, are acting on pickup ions at the Martian terminator. A possibility is a viscous-like interaction between the Solar Wind and the Martian ionosphere at low altitudes.