MORPHOLOGY AND TIME-VARIATION OF THE JOVIAN FAR UV AURORA - HUBBLE-SPACE-TELESCOPE OBSERVATIONS

High spatial resolution images of the north polar region of Jupiter have been obtained with the Faint Object Camera on board the Hubble Space Telescope. The first set of two images collected 87 min apart in February 1992 shows a bright (congruent-to 180 kR) emission superimposed on the background in rotation with the planet. Both Ly alpha images show common regions of enhanced emission but differences are also observed, possibly due to temporal variations. The second group of images obtained on June 23 and 26, 1992 isolates a spectral region near 153 nm dominated by the H-2 Lyman bands and continuum. Both pictures exhibit a narrow arc structure fitting the L = 30 magnetotail field line footprint in the morning sector and a broader diffuse aurora in the afternoon. They show no indication of an evening twilight enhancement. Although the central meridian longitudes were similar, significant differences are seen in the two exposures, especially in the region of diffuse emission, and interpreted as signatures of temporal variations. The total power radiated in the H-2 bands is congruent-to 2 x 10(12) W, in agreement with previous UV spectrometer observations. The high local H-2 emission rates (approximately 450 kR) imply a particle precipitation carrying an energy flux of about 5 x 10(-2) W m-2.