Simultaneous Spectroscopy and Imaging of the Jovian Aurora with the Hopkins Ultraviolet Telescope and the Hubble Space Telescope
Simultaneous ultraviolet spectra and images of the north polar aurora of Jupiter were obtained on 1995 March 9 with the Hopkins Ultraviolet Telescope (HUT) and the Hubble Space Telescope (HST). This unique data set contains a well-calibrated flux measurement that includes all of the H2 Lyman and Werner band emission from 900 to 1650 Å, as well as information about the spatial extent of the aurora. For these observations, we oriented the 10" × 57" slit of the HUT spectrograph parallel to the equator of Jupiter so that it was underfilled by the aurora and minimally contaminated by extraneous reflected solar light from low to mid latitudes. The aurora was imaged simultaneously using the HST Wide Field and Planetary Camera 2 (WFPC2). Images were taken through a Wood's filter and also through a Wood's filter/CaF2 filter combination. These images have recorded the aurora in the light of atomic and molecular hydrogen with relatively low reflected solar contamination. The molecular hydrogen aurora is found to extend over 4.5 +/- 0.5 × 10-10 sr, with an average brightness of 106 +/- 12 kR integrated over the band of wavelengths from 900 to 1650 Å, excluding H I λ1216. We measure a 13% larger emitting area (5.1 +/- 0.5 × 10-10 sr) and significantly different morphology for the combined atomic and molecular hydrogen aurora (Lyα + H2), although these differences could be a result of time variability. Color ratios derived from the data indicate a total auroral energy deposition rate of 13 ergs s-1 cm-2 by 3-30 keV electrons. We find little evidence for ions as primary auroral particles in the HUT spectra. Our analysis places upper limits on sulfur ion emissions that are an order of magnitude lower than those from the IUE observations, and, therefore, the emissions could be entirely from the Io torus in the background of the planet.