Hydrodynamic Instability of the Heliopause Driven by Plasma -

Results from time-dependent two-dimensional hydrodynamic simulations of the global heliosphere show that drag between the plasma ions and the interstellar neutrals, caused by charge-exchange collisions, causes the heliopause to be hydrodynamically unstable. Both ions and neutrals are treated as uids coupled by charge-exchange collisions. The neutral-ion drag proportional to the plasma density introduces an eeective gravity in the direction of the neutral ow, and because the interstellar plasma is much denser than the heliosheath plasma, a Rayleigh-Taylor like instability develops. The heliopause is unstable only near the stagnation point at the \nose" of the heliosphere. In the simulations, the heliopause is seen to oscillate nonlinearly about its equilibrium position with a time scale on the order of a hundred years and amplitudes of tens of AUs. Growth rates from the simulations are in reasonable agreement with theoretical estimates. Implications of this instability on the interpretation of the Voyager 2-3 kHz emissions are discussed. 2