Has the configuration of Jupiter's polar aurora changed significantly since the Voyager epoch?

At Earth, over 70 percent of auroral power during active periods resides within the diffuse auroral components, despite the disproportionate interest in discrete auroral processes. At Jupiter, present day interest also resides overwhelmingly on discrete auroral processes associated with field-aligned currents driven by planetary rotation. However, during the Voyager epoch of 1979 through the 1980's, interest was focused elsewhere. It was believed that bright aurora of Jupiter extend in latitude down to the vicinity of the magnetic footprints of the plasma torus of Io, based on Voyager ultraviolet spectrometer (UVS) observations. And, it was believed that diffuse auroral processes generate this Io-associated aurora, specifically with the precipitation of energetic ions, most importantly S and O. Ion energy intensities were measured sufficient to deliver about 60 ergs per square cm over the 7 to 9 RJ region with strong wave scattering, sufficient to deliver about 30 trillion W of energy. Since that time (beginning in the early 1990's), near-Earth imaging of the aurora has revealed that the brightest aurora of Jupiter typically occurs on field lines that map along field lines to between 20 and 30 RJ, and certainly no closer to Jupiter than 15 RJ. Discussions of the differences between Voyager and more recent observations have focused on the limitations of the Voyager measurements. However, the particles that were identified during the Voyager epoch as being responsible for the bright aurora are just the same particles that in 1995 were observed by Galileo to have been dramatically depleted, by a factor of 5 in total energy density and perhaps even more for heavy ions. Could the change in the perceived configuration of the aurora since the Voyager epoch represent a true change in the configuration of Jupiter's magnetosphere? Specifically, has a key component of Jupiter's aurora, the diffuse component, dimmed dramatically since that epoch? Here we update the evidence that the configuration of Jupiter's magnetosphere has changed by showing that the depletion of the near-torus energetic ion populations have persisted and probably substantially deepened in more recent times. We review concurrent evidence that the depletion of the energetic ions is caused by enhancements in the neutral gases emanating from Io since the Voyager epoch. We argue that following the Voyager epoch, Jupiter's aurora may have become even less Earth-like than it is now in terms of the balance between diffuse and discrete components, and that the volcanoes of Io have a here-to-fore unappreciated role in establishing that balance.