HIGH-RESOLUTION SPECTRA OF JUPITER NORTHERN AURORAL ULTRAVIOLET EMISSION WITH THE HUBBLE-SPACE-TELESCOPE

The first spectroscopic observations of planetary aurora with the HST are reported. These include spectral regions centered on the H-2 Lyman and Werner bands of a region of Jupiter's northern aurora. The observ ations were made with the Goddard High Resolution Spectrograph (GHRS) using the Large Science Aperture as part of a campaign to study Jupite r at the time of the Ulysses flyby. The individual rotational-vibratio nal bands are resolved and the observed emissions are essentially all from H-2. A rotational-vibrational temperature for H-2 of 530 +/- 100 K is derived, a value significantly less than the 850-1100 K reported for Jovian H-3(+) in the near-infrared but consistent with the tempera ture reported for fundamental-band quadrupole H-2 emission. Comparison with the Faint Object Camera (FOC) images shows that the observed reg ion was not one of the hot spots of the aurora. The results are interp reted in terms of electron impact excitation of H-2 from secondary par ticles generated by primaries precipitating into Jupiter's atmosphere from the magnetosphere. In the region of the aurora observed, the homo pause level is found to be significantly hotter but not necessarily hi gher than observed at nonauroral latitudes. The equatorial H-2 dayglow spectrum was also detected; its intensity was 3.2 kR or 13% of the st rength of the observed auroral emission.