Pressure‐Balanced structures between 1 AU and 24 AU and their implications for solar wind electrons and interstellar pickup ions

“Pressure‐balanced structures” (PBSs) in the heliosphere are microscale phenomena with a characteristic length along the radial dimension of the order of 0.05 AU across which the sum of the thermal pressures and the magnetic pressure is constant. We have identified pressure‐balanced structures in the Voyager data from 1 AU to 24 AU. If the density of pickup ions Ni were proportional to the proton density across a PBS and if the electron pressure were negligible, then from measurements of the magnetic field and the proton density and temperature across pressure balanced structures we derive a pickup ion density which is significantly smaller than the density predicted by a model based on the same assumption. This suggests that there are processes which “smear out” the pressure of the pickup ions so that it is nearly constant on the scale of a PBS. If the pressure of the pickup ions is uniform across a PBS, then one can determine the electron temperature from the pressure balance condition. The electron temperatures derived from the PBS are consistent with the directly measured electron temperatures in the region within 5 AU, and they are consistent with the extrapolation of the polytropic relation between the electron temperature and density derived by Sittler and Scudder (1980) for densities of ≥0.03 cm−3. From 11 pressure‐balanced structures between 18.9 AU and 21.0 AU we derive an average temperature Te = (5.2±2.3) × 104 °K at ∼20 AU.