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

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Abstract
Observations of the jovian system in the near-infrared (3.4 μm) reveal a wealth of information about Jupiter's magnetic field, magnetosphere, and magnetospheric dynamics. This wavelength contains a few emission lines of the H3+ ion and it is centred on a deep methane absorption band. 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, from 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 H3+ 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.

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