THE VECTOR DIRECTION OF THE INTERSTELLAR MAGNETIC FIELD OUTSIDE THE HELIOSPHERE

We propose that magnetic reconnection at the heliopause (HP) only occurs where the interstellar magnetic field points nearly anti-parallel to the heliospheric field. By using large-scale magnetohydrodynamic (MHD) simulations of the heliosphere to provide the initial conditions for kinetic simulations of HP reconnection, we show that the energetic pickup ions downstream from the solar wind termination shock induce large diamagnetic drifts in the reconnecting plasma and stabilize non-anti-parallel reconnection. With this constraint, the MHD simulations can show where HP reconnection most likely occurs. We also suggest that reconnection triggers the 2-3 kHz radio bursts that emanate from near the HP. Requiring the burst locations to coincide with the loci of anti-parallel reconnection allows us to determine, for the first time, the vector direction of the local interstellar magnetic field. We find it to be oriented toward the southern solar magnetic pole.