High-resolution spectra of Jupiter's northern auroral ultraviolet emission with the Hubble Space Telescope

The first spectroscopic observations of planetary aurora with the Hubble Space Telescope (HST) are reported. These include spectral regions centered on the H2 Lyman and Werner bands of a region of Jupiter's northern aurora. The observations were made with the Goddard High Resolution Spectrograph (GHRS) using the Large Science Aperture as part of a campaign to study Jupiter at the time of the Ulysses flyby. The individual rotational-vibrational bands are resolved and the observed emissions are essentially all from H2. A rotational-vibrational temperature for H2 of 530 +/- 100 K is derived, a value significantly less than the 850-1100 K reported for Jovian H3(+) in the near-infrared but consistent with the temperature reported for fundamental-band quadrupole H2 emission. Comparison with the Faint Object Camera (FOC) images shows that the observed region was not one of the hot spots of the aurora. The results are interpreted in trms of electron impact excitation of H2 from secondary particles generated by primaries precipitating into Jupiter's atmsophere from the magnetosphere. In the region of the aurora observed, the homopause level is found to be significantly hotter but not necessarily higher than observed at nonauroral latitudes. The equatorial H2 dayglow spectrum was also detected; its intensity was 3.2 kR or 13% of the strength of the observed auroral emission.