HST-FOC observations of a remarkable UV auroral event on Jupiter

Two sets of UV (ultraviolet) images of the Jovian north aurora were obtained with the Faint Object Camera (FOC) on Hubble. The first series shows a very intense discrete arc in corotation with the planet. The maximum apparent H2 emission rate corresponds to an electron precipitation of approximately 1/sq Wm, a very large flux in comparison with the solar EUV (extreme ultraviolet) heating. The hugh particle heating rate of the auroral upper atmosphere of Jupiter is expected to cause a large transient temperature increase and generate strong thermospheric winds. Twenty hours later, the discrete arc had considerably decreased in brightness. The timescale and magnitude of the change in the UV aurora strongly suggests that the discrete Jovian auroral precipitation is related to large scale current system variations as are the Earth's discrete aurorae.