Is the magnetosphere of Jupiter more energetic in the Juno era?

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23 July 2024


Ganymede, the only magnetized moon in our Solar System, orbits deep inside the giant magnetosphere of Jupiter where it interacts with the temporally and spatially variable magnetized disk of plasma in corotation around the planet, its magnetodisk. The intensities of ions and electrons precipitating to the surface of Ganymede in particular depend on the location of the moon with respect to the Jovian magnetodisk. A team from the Institut de recherche en astrophysique et planétologie (IRAP-OMP – CNES/CNRS/UT3) and from the Institut Supérieur de l’Aéronautique et de l’Espace (ISAE-SUPAERO) provides a full quantification of electron properties along the orbit of Ganymede as observed by Juno. When comparing their results with Galileo-based observations and models, they reported that the latter two underestimated electrons fluxes, by a factor 2 to 9, in particular at high energies, between 20 keV and 2 MeV.

This is done by combining observations obtained during five years around Jupiter from two instruments onboard Juno – the Jovian Auroral Distributions Experiment (JADE) to which IRAP contributed and the Jupiter Energetic particle Detector Instrument (JEDI) – in order to build composite electron energy spectra and derive their omnidirectional fluxes, densities, and pressures.


The magnetosphere of Jupiter with its radiation belts.
Credit: NASA/JPL, https://www.missionjuno.swri.edu/media-gallery/magnetosphere

The IRAP Team reported that the average electron omnidirectional fluxes are significantly attenuated when measured above or below the magnetodisk, as well as strongly inside the magnetosphere of the moon where its intrinsic magnetic field provides additional shielding. They confirmed that the electron total density is dominated by the thermal population, whereas the total pressure is dominated by the suprathermal one.

The method developed during this study can be adapted and applied to characterize the electron and ion plasma environments where Galilean moons orbit. Such a detailed characterization will make it possible to constrain input parameters for numerical simulations dedicated to the study of planetary space weather and the moon-magnetosphere interactions at Jupiter, as well as to refine empirical environmental and radiation models at each of them for current and future space missions like the Jupiter Icy moon Explorer (JUICE).

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