Details

Autor(en) / Beteiligte

• Pelcener, S.
• André, N.
• Nénon, Q.
• Rabia, J.
• Rojo, M.
• Kamran, A.
• Blanc, M.
• Louarn, P.
• Penou, E.
• Santos‐Costa, D.
• Allegrini, F.
• Ebert, R. W.
• Wilson, R. J.
• Szalay, J.
• Mauk, B. H.
• Paranicas, C.
• Clark, G.
• Bagenal, F.
• Bolton, S.

Titel

Temporal and Spatial Variability of the Electron Environment at the Orbit of Ganymede as Observed by Juno

Ist Teil von

• Journal of geophysical research. Space physics, 2024-05, Vol.129 (5), p.n/a

Ort / Verlag

Washington: Blackwell Publishing Ltd

Erscheinungsjahr

2024

Quelle

Wiley Online Library All Journals

Beschreibungen/Notizen

• The thermal and energetic electrons along Ganymede's orbit not only weather the surface of the icy moon, but also represent a major threat to spacecraft. In this article, we rely on Juno plasma measurements to characterize the temporal and spatial variability of the electron environment upstream of Ganymede. In particular, we find that electron spectra observed by Juno have fluxes larger by a factor of 2–9 at energies above 10 keV than what was measured two decades earlier by Galileo. This result will advance our understanding of the surface weathering and may be a concern for the radiation safety of the JUICE mission. Furthermore, the June 2021 close fly‐by of Ganymede through the moon's wake reveals that the open field line regions of its magnetosphere attenuate electron fluxes at all energies by a factor of 1.6–5, thereby offering a natural shelter to visiting spacecraft crossing this region. Plain Language Summary 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. In this work, we provide a full quantification of electron properties along the orbit of Ganymede as observed by Juno. This is done by combining observations from two instruments in order to build composite electron energy spectra and derive their omnidirectional fluxes, densities, and pressures. We report 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. We confirm that the electron total density is dominated by the thermal population, whereas the total pressure is dominated by the suprathermal one. When comparing our results with Galileo‐based observations and models, we find that the latter the latter two underestimate fluxes in particular at high energies, and we put these observations in context for the future exploration of Ganymede by JUICE. Key Points We present composite electron energy spectra combining all Juno particle data from 07/2017 to 08/2022 at Ganymede's orbit We study the variability of electron fluxes inside and outside the Jovian magnetodisk as well as within Ganymede's magnetosphere Galileo‐based models underestimate the electron fluxes observed by Juno in particular at high energies