Voyager observations in the outer heliosphere and interstellar medium

The Voyager spacecraft are making the first direct plasma measurements of the heliosheath and interstellar medium. This paper discusses the differences in the heliosheath observations of Voyager 1 (V1) and Voyager 2 (V2), the V1 heliopause crossing, and observations of transient structures in the local interstellar medium (LISM). The heliosheath velocities at V1 are smaller than expected throughout the heliosheath and are zero in the stagnation region, which persists for 8 AU before the heliopause crossing. The V2 flow profile is very different from that at V1; the average speed stays constant at 145 km/s but the flow has turned over 60° from radial. The heliopause crossing region has numerous structures in cosmic rays, termination shock particles, and magnetic field so that the exact heliopause crossing point is still controversial. Solar transients drive shocks which propagate through the LISM, generate anisotropies and intensity changes in the galactic cosmic rays (GCRs) and excite plasma and radio waves.