Termination Shock Particle Streaming Upstream at New Horizons

A couple years before Voyager 1 and Voyager 2 (V2) crossed the termination shock (TS), instruments on board both spacecraft observed high intensities of accelerated termination shock particles (TSPs) beaming in opposite directions. This phenomenon was explained by magnetic field lines connecting the spacecraft to the TS prior to the crossings. The opposite streaming of TSPs is due to an east–west asymmetry of the TS caused by the interstellar magnetic field building up on the outside of the heliopause. Here, we examine the magnetic connectivity for New Horizons (NH) ahead of the TS with a global MHD model with steady solar wind conditions. Our model predicts that NH will observe particles streaming in the same direction as V2 (+T direction in the RTN coordinate system), 1.0 ± 0.7 au from the TS. We then estimate the average speed of the TS during the V2 TS crossing to be 2.5 au yr−1 outward, based on the timing and distance of the TS at the onset of the TSP observations and the crossing itself. Using this speed, we find that NH will have a 0.2 yr warning prior to crossing the TS if the TS is moving inward at the time of the crossing and a 2.4 yr warning if the TS is moving outward.