Images of Excited H 3 + at the Foot of the Io Flux Tube in Jupiter's Atmosphere

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Abstract
The electrodynamic interaction between Io and the Jovian magnetosphere drives currents to and from the planet's ionosphere, where H 3 + emission is excited. Direct images of this phenomenon were obtained with the ProtoCAM infrared camera at the National Aeronautics and Space Administration's 3-m Infrared Telescope Facility. The emissions are localized to the instantaneous foot of the Io flux tube, ≈8° equatorward of the more intense auroral H 3 + emission associated with higher magnetic latitudes. The foot of the Io flux tube leads that of (undisturbed) model magnetic field lines passing through Io by 15° to 20° in longitude and is less visible in the northern hemisphere at longitudes where the surface magnetic field strength is greatest. These data favor the unipolar inductor model of the Io interaction and provide insight into the source location and generation of Jovian decameter radio emission.