Variations of Ganymede's auroral footprint locations are presented based on observations by the Hubble Space Telescope in 2007 and 2016. The poleward and equatorward shifts of Ganymede's footprint could be influenced by the mass outflow rate from Io and the solar wind compression, as the internal and external factors respectively. We compare our results with Ganymede's footprint mapping based on the magnetodisc model. The mapped footprint in Jupiter's ionosphere shifts equatorward with increased hot plasma parameter, Kh, which is associated with hot plasma pressure. We analyzed the effect of cold plasma number density (Nc), related to the mass outflow rate and connected to the material produced by Io. The results show that the magnetic footprint is shifted equatorward by 0.37° when the mass outflow rate is increased from 800–2,000 kg s−1. Iogenic plasma has a strong influence on the stretching of the magnetic field lines in Jupiter's middle magnetosphere, causing the equatorward shift of Ganymede's footprint. For external factors, Ganymede's footprint shifted poleward by 0.62° under the influence of solar wind compression while the mass outflow is kept constant at 1,000 kg s−1. We present similar locations of Ganymede's footprint based on the field lines mapped as a result of the compensation between an increase of Kh and the solar wind compression. Overall, the location of Ganymede's auroral footprint corresponds with the mass loading rate from Io and the solar wind dynamic pressure.

Jupiter’s aurora features have been observed by the Hubble space telescope (HST) for over two decades. One of the auroral features, Ganymede’s magnetic footprint, appears close to the main emission and is sometimes embedded in the main emission. The latter case causes difficulty in identifying Ganymede’s magnetic footprint from in the main emission. The FUV aurora images were taken by Advanced Camera for Surveys (ACS) onboard the HST. The fluctuations of Ganymede’s footprint brightness over time will be analyzed. Moreover, the correlation between the brightness and locations of the main emission and Ganymede’s magnetic footprint will be analyzed to characterize the connection between ionospheric phenomena and the magnetospheric dynamics. Since the main emission is very bright in comparison with the footprint, therefore, the variation of the main emission can affect the Ganymede’s magnetic footprint. Furthermore, the expansion of the main emission is consistent with the location shift of Ganymede’s magnetic footprint in equatorward direction. The brightness and location of the main emission can be influenced by the plasma variation in Jupiter’s magnetosphere which is affected partly by the volcanic eruption on Io and solar wind dynamic pressure. The variation of Ganymede magnetic footprint’s brightness and location in respond to the main emission could be an important indicator of the magnetospheric variation under the influences of internal and external factors.

The brightness of Io's magnetic footprint, an indicator of electromagnetic interaction at the satellite, appears to be strongly connected to the satellite's distance from the plasma equator. As a result, the brightest footprints were detected when Io is near the interception location between the satellite's orbital plane and the plasma equator. However, volcanic activities on Io show strong correlation with the equatorward shift of Jupiter's main auroral oval, consequently causing the disappearance of Io's footprint.