ULTRAVIOLET IMAGING OF THE JOVIAN AURORA WITH THE HUBBLE SPACE TELESCOPE

We present here for the first time a Lyman-alpha image of the north polar region of Jupiter obtained with the Faint Object Camera (FOC) on board the Hubble Space Telescope a few hours after the encounter of the ULYSSES spacecraft with Jupiter. The presence of high latitude regions of enhanced emission is clearly observed. A comparison with the location of the "UVS oval", the Io (L = 6) and high-latitude field-line footprints shows that the best agreement is obtained with the L greater-than-or-equal-to 15 footprint and the UVS oval which are close to each other for the particular longitudinal sector (30-degrees < lambda(III) < 210-degrees) observed. These two L-shells correspond to two possible sources of precipitation: particles originating respectively from the region of the plasma torus of Io in a distorted magnetic field or particles from the distant magnetosphere by analogy with the terrestrial aurora. The first direct determination of the latitudinal extent of the oval and of its intensity is made and compared with previous estimates.