UV Io footprint leading spot: A key feature for understanding the UV Io footprint multiplicity?

The electromagnetic interaction between Io and the Jovian magnetosphere generates a UV auroral footprint in both Jovian hemispheres. Multiple spots were observed in the northern Jovian hemisphere when Io was in the northern part of the plasma torus and vice-versa for the South. Based on recent Hubble Space Telescope (HST) measurements, we report here the discovery of a UV leading spot, i.e., a faint emission located ahead of the main spot. The leading spot emerges at System III longitudes between 0 degrees and 100 degrees in the northern hemisphere and between 130 degrees and 300 degrees in the southern hemisphere, i. e., in one hemisphere when multiple spots are observed in the other hemisphere. We propose as one potential mechanism that electron beams observed near Io are related to the generation of the leading spot and the secondary spot in the opposite hemisphere.