Enhancement of Pickup Ion Pressure in the Inner Heliosheath and Possible Implications for Energetic Neutral Atom (ENA) Observations by IBEX

The measurements taken by Voyager 2 at the heliospheric termination shock (HTS) crossing revealed that a very small percentage of the upstream solar wind flow energy is converted to downstream thermal ion heating. Instead, most of the upstream kinetic or ram energy used to heat non-thermalized pickup ions (PUIs) (Richardson et al. 2018). Voyager 2 observations show that the inner heliosheath (IHS) is dominated by a large energetic particle pressure (Decker et al. 2015) and the plasma beta, when the energetic particle pressure is included, is as much as about 14. Interplanetary shocks that collide with the HTS propagate into the IHS until they collide with the heliopause (HP). These shocks are partially reflected back into the subsonic IHS region, and partially transmitted into the very local interstellar medium (VLISM) (Washimi et al. 2011). Because of the large PUI pressure in the IHS, shocks propagating in this region are mediated by the energetic PUIs, and the PUIs represent the primary dissipation mechanism for quasi-perpendicular IHS shocks. This results in further heating of the PUI component in the IHS rather than heating of the subsonic thermal solar wind plasma. Consequently, IHS shocks enhance the IHS PUI thermal pressure. The mediation of the IHS temperature due to the presence of many shocks may result in the more effective production of ENAs due to charge exchange between interstellar neutral gas and IHS PUIs, which should be observed in IBEX ENA measurements. We also suggest that there might be a correlation between ENA flux differences between solar maximum and solar minimum. We study the structure of shock waves in the IHS and show that these shocks are mediated by PUIs.