Alternating north-south brightness ratio of Ganymede's auroral ovals: Hubble Space Telescope observations around the Juno PJ34 flyby

Abstract

We report results of Hubble Space Telescope observations from Ganymede's orbitally trailing side which were taken around the flyby of the Juno spacecraft on June 7, 2021. We find that Ganymede's northern and southern auroral ovals alternate in brightness such that the oval facing Jupiter's magnetospheric plasma sheet is brighter than the other one. This suggests that the generator that powers Ganymede's aurora is the momentum of the Jovian plasma sheet north and south of Ganymede's magnetosphere. Magnetic coupling of Ganymede to the plasma sheet above and below the moon causes asymmetric magnetic stresses and electromagnetic energy fluxes ultimately powering the auroral acceleration process. No clear statistically significant time variability of the auroral emission on short time scales of 100s could be resolved. We show that electron energy fluxes of several tens of mW m${}^{-2}$ are required for its OI 1356 Å emission making Ganymede a very poor auroral emitter.

arXiv commentAccepted for publication with Geophys. Res. Let

References in corpus (4)

• HST/STIS Ultraviolet Imaging of Polar Aurora on Ganymede
• A sublimated water atmosphere on Ganymede detected from Hubble Space Telescope observations
• Ganymede MHD Model: Magnetospheric Context for Juno's PJ34 Flyby
• Brown dwarfs as ideal candidates for detecting UV aurora outside the Solar System: Hubble Space Telescope observations of 2MASS J1237+6526

Cited by in corpus (4)

• Ganymede MHD Model: Magnetospheric Context for Juno's PJ34 Flyby
• A patchy CO${}_2$ exosphere on Ganymede revealed by the James Webb Space Telescope
• Short-Timescale Spatial Variability of Ganymede's Optical Aurora
• Constraining Electron-Impact Ionization of O${}_2$ Through UV Aurora Observations at Ganymede