Goings-on in Jupiter's auroras: Periodic emission within Jupiter’s main auroral oval and short timescale variations in the motion of the Ganymede footprpint

In this presentation we discuss some results from a programme of Hubble Space Telescope observations of Jupiter’s FUV auroras obtained during 2016. In particular, we have discovered pulsating emission within Jupiter’s main auroral oval, providing evidence of the auroral signature of Jovian ULF wave processes. The form comprises a 1° × 2° spot located directly on the main emission, whose intensity oscillates with a period of ~10 min throughout the 45 min observation. The feature appears on the duskward edge of the discontinuity, maps to ~13– 14 h LT and ~20– 50 RJ, and rotates at around a half of rigid corotation. We show that the period of the oscillation is similar to the expected Alfvén travel time between the ionosphere and the upper edge of the equatorial plasma sheet in the middle magnetosphere, and we thus suggest that the pulsating aurora is driven by a mode confined to the low-density region outside the plasma sheet. We also discuss the discovery of short (10 min) timescale variations in the location of the Ganymede auroral footprint, which possibly indicate changes in the ambient plasma density near Ganymede.