A new "Reference Oval" for Jupiter's FUV Aurora

The observation of Jupiter's FUV aurora during the Cassini Jupiter flyby has almost doubled the number of available HST-STIS images of Jupiter's poles. This large 2-month-dataset has been statistically analyzed to provide a new "reference oval", actually a statistical average location of the auroral emission, both in the North and in the South. This study clearly shows that the auroral morphology is CML dependent, meaning that substantial local time effects take place during one Jovian rotation. Consequently, the new "reference oval" is described as a set of statistical average locations as a function of CML range. A more detailed analysis shows time variation of the morphology within timescales ranging from weeks to hours which might be attributed to changing conditions in the magnetosphere. This study provides a quantitative basis for future morphological analysis and correlation of the FUV aurora with auroral features observed with other instruments at different wavelengths, such as the Chandra x-ray observatory or the IRTF telescope. This statistical average is of prime importance for estimating the origin and nature of the impinging particles giving rise to the auroral emission. It also provides crucial constraints for the modeling of the Jovian magnetosphere, and the energy inputs to Jupiter's upper atmosphere.