Structure and dynamics of the solar wind/ionosphere interface on Mars: MEX-ASPERA-3 and MEX-MARSIS observations

The measurements of the local plasma parameters of the ionospheric and solar wind plasmas and the magnetic field strength carried out by the ASPERA-3 and MARSIS experiments onboard Mars Express (MEX) in the subsolar region of the induced Martian magnetosphere provide us with a first test of the pressure balance across the solar wind/ionosphere interface. The structure of this transition is very dynamic and is controlled by the solar wind. For a broad range of the solar wind dynamic pressures, the magnetic field in the boundary layer raises to the values just sufficient to balance the solar wind pressure. The magnetic field frozen into the electrons is transported across the magnetospheric boundary (MB) where solar wind terminates and the planetary plasma begins to prevail. The dense ionospheric plasma has a sharp outer boundary the position of which is usually a little closer to the planet than the MB. Although the number density reaches on this boundary similar to 10(3) cm(-3) the contribution of the ionospheric thermal pressure is rather small and the ionosphere is magnetized. There are also cases when the magnetic field almost does not vary across both boundaries.