Pickup Ion Pressure in the Outer Heliosphere Built from the Local Cloud Neutral Densities

Most of the pressure that pushes back against the interstellar medium at the edge of the solar system is not carried by the solar wind protons that left the Sun, but by pickup ions: interstellar neutrals that drifted in from the local cloud, were ionised, and were swept up to solar wind speed. Building their pressure from the cloud neutral density, the filtration factor and the wind speed gives a pickup ion pressure near the termination shock of P/k = 5,169 K per cubic centimetre, about 0.43 of the wind ram pressure there, consistent with the Voyager finding that the shocked wind's thermal pressure fell short of expectations because a large share resided in the pickup population. The estimate is computed from stated published inputs with the deposited script, not measured here.