A REMARKABLE AURORAL EVENT ON JUPITER OBSERVED IN THE ULTRAVIOLET WITH THE HUBBLE-SPACE-TELESCOPE

Two sets of ultraviolet images of the Jovian north aurora were obtained with the Faint Object Camera on board the Hubble Space Telescope. The first series shows an intense discrete are in near corotation with the planet. The maximum apparent molecular hydrogen emission rate corresponds to an electron precipitation of similar to 1 watt per square meter, which is about 30,000 times larger than the solar heating by extreme ultraviolet radiation. Such a particle heating rate of the auroral upper atmosphere of Jupiter should cause a large transient temperature increase and generate strong thermospheric winds. Twenty hours after initial observation, the discrete are had decreased in brightness by more than one order of magnitude. The time scale and magnitude of the change in the ultraviolet aurora leads us to suggest that the discrete Jovian auroral precipitation is related to large-scale variations in the current system, as is the case for Earth's discrete aurorae.