Energetic neutral atom imaging of the heliospheric boundary region

Energetic neutral atom (ENA) imaging is a powerful technique, which can rem otely probe the properties of distant hot plasmas. Hot plasmas are abundant at the heliospheric boundary, the region where the expanding solar wind me ets the surrounding local interstellar cloud. Here we present a new concept for imaging this boundary in ENA fluxes. Heliospheric ENAs are born from c harge exchange between energetic protons and the background interstellar at omic hydrogen gas. The technique is ideal for studying the asymmetric three -dimensional heliospheric interface region remotely, from 1 AU. We show tha t ENA imaging in the 0.2-6 keV energy range will establish the nature of th e termination shock and properties of hot proton populations in the heliosh eath. We also examine how the evolution of pickup proton populations at and beyond the shock can be explored. Global heliosphere ENA images will disti nguish among the competing models of the interaction between the Sun and th e local interstellar medium, and they will reveal the physics of important processes in the interface region. Heliospheric ENA fluxes are exceptionall y weak, which makes imaging implementation difficult. Nonetheless, we show how single-pixel ENA sensors can image the heliosphere from a spinning spac ecraft on a typical mission near 1 AU. The required instrumentation is brie fly discussed.