Bi-ion discontinuities at weak solar wind massloading

The interaction of the solar wind (SW) with a small-scale heavy ion source is studied in the framework of the bi-ion fluid theory, where light and heavy ions are treated as separate, electromagnetically coupled fluids. For small scales (of the order of the inertial length) both ion species behave almost as unmagnetized allowing thus large relative velocities between them. The phase velocity of magneto-acoustic waves propagating transverse to the magnetic field was determined as a function of the relative velocity for different heavy ion abundances. Besides the up- and down-shifted proton mode a slow mode with low phase velocities (near to the heavy ion Alfven velocity) exists. It is shown, that for weak solar wind massloading bi-ion magneto-acoustic oscillations of all plasma parameters occur in spatial regions, where the heavy ion flow velocity meets the slow mode phase velocity. This is related to the periodic formation of bi-ion discontinuities. Comparison with 1D hybrid code results indicates that kinetic effects are of minor importance for the underlying processes. 2D fluid simulations are in good agreement with effects observed in space, as the quasi-periodic oscillations at the AMPTE releases. Predictions are made also for the solar wind interaction with weak comets (related to the ROSETTA mission), Deimos and Pluto.