ENA Imaging of Planetary Ring Currents

Basic techniques of ENA cameras are presented followed by an overview of an inversion technique applied to ENA images obtained by the High Energy Neutral Atom (HENA) camera on board the Imager for Magnetopause-to-Aurora Global Exploration (IMAGE) mission. Observations from HENA are used to demonstrate the storm-time evolution and acceleration of the ring current ions. Plasma pressure retrieved from HENA images are used to illustrate the three-dimensional structure of the partial ring current (PRC) system. ENA observations of the Saturnian magnetosphere by the Ion and Neutral Camera (INCA) on board Cassini are used to contrast its force balance of the Saturnian magnetosphere with that of Earth. The dynamics of Saturn's magnetosphere are reviewed showing Earth-like phenomena such as large-scale injections not unlike those at Earth. A brief review is given of the only ENA observations of the Jovian magnetosphere by INCA during the Cassini flyby showing relatively stable ENA emissions indicating a presence of a Europa torus. A description of the future ENA observations of the Jovian magnetosphere on board the Jupiter Icy Moon Explorer (JUICE) by the European Space Agency (ESA) is given. The paper concludes by contrasting ENA imaging of the three planetary inner magnetospheres and summarizing future directions.