The H3+ ion:: a remote diagnostic of the jovian magnetosphere

Observations of the jovian system in the near-infrared (3.4 mu m) reveal a wealth of information about Jupiter's magnetic field, magnetosphere, and magnetospheric dynamics. This wavelength contains a few emission lines of the H-3(+) ion and it is centred on a deep methane absorption hand. As a result, one can image Jupiter's ionosphere at this wavelength with extraordinary signal-to-noise ratio, against a planet otherwise darkened by absorption due to methane in its atmosphere. High spatial resolution images of the planet's surface provide a synoptic view of the entire magnetosphere, fr-om the electrodynamics of Io and the torus, to the excitation of auroral displays at high magnetic latitude. Observations of the Io Flux Tube footprint have provided a new magnetic coordinate system for the jovian polar regions and new insight into the electrodynamic interaction between Jupiter and Io. Short-term temporal variations (days) of auroral intensity are observed in the IR and are well correlated with variations in the solar-wind ram pressure arriving at Jupiter. These H-3(+) emissions are thermally excited and are a good proxy for time-averaged energy deposition. It is now possible to produce detailed maps of energy deposition from the Io footprint (L = 6) to the pole, in which both system III and local time variations are evident.