The Effects of a Local Interstellar Magnetic Field on Voyager 1 and 2 Observations

We show that an interstellar magnetic field can produce a north-south asymmetry in the solar wind termination shock. Using Voyager 1 and 2 measurements, we suggest that the angle α between the interstellar wind velocity and the magnetic field is 30° < α < 60°. The distortion of the shock is such that termination shock particles could have streamed outward along the spiral interplanetary magnetic field connecting Voyager 1 to the shock when the spacecraft was within ~2 AU of the shock. The shock distortion is larger in the southern hemisphere, and Voyager 2 could be connected to the shock when it is within ~5 AU of the shock, but with particles from the shock streaming inward along the field. Tighter constraints on the interstellar magnetic field should be possible when Voyager 2 crosses the shock in the next several years.