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M‐Shell and Local Time Variability of the Electron and Magnetic Environments at the Orbit of Callisto as Observed by the Juno and Galileo Missions.

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Title:	M‐Shell and Local Time Variability of the Electron and Magnetic Environments at the Orbit of Callisto as Observed by the Juno and Galileo Missions.
Authors:	Le Liboux, T.^1,2 (AUTHOR) thomas.le-liboux@latmos.ipsl.fr, André, N.^1,3 (AUTHOR), Modolo, R.² (AUTHOR), Nénon, Q.¹ (AUTHOR), Seves, A.¹ (AUTHOR), Rabia, J.¹ (AUTHOR), Rojo, M.¹ (AUTHOR), Kamran, A.¹ (AUTHOR), Liu, Z.‐Y.¹ (AUTHOR), Leblanc, F.² (AUTHOR), Blanc, M.¹ (AUTHOR), Louarn, P.¹ (AUTHOR), Penou, E.¹ (AUTHOR), Santos‐Costa, D.⁴ (AUTHOR), Allegrini, F.^4,5 (AUTHOR), Ebert, R. W.^4,5 (AUTHOR), Wilson, R. J.⁶ (AUTHOR), Szalay, J. R.⁷ (AUTHOR), Paranicas, C.⁸ (AUTHOR), Clark, G.⁸ (AUTHOR)
Source:	Journal of Geophysical Research. Space Physics. Aug2025, Vol. 130 Issue 8, p1-24. 24p.
Subject Terms:	Magnetosphere, Electron distribution, Callisto (Satellite), Magnetospheric physics, Jupiter (Planet), Exploration of Jupiter, Juno (Space probe)
Abstract:	Jupiter's moon Callisto orbits in a highly variable magnetospheric environment depending on its position relative to the Jovian current sheet. The Juno and Galileo missions have visited the Jovian magnetosphere and crossed Callisto's orbit several times in a variety of configurations, providing an opportunity to better characterize Callisto's orbital environment. The aim of this work is to characterize the variability of Jupiter's magnetospheric environment properties at Callisto's orbit. After identifying the time intervals during which both missions crossed the moon's orbit, Juno's charged particle data from the Jupiter Energetic Particle Detector Instrument and the Jovian Auroral Distributions Experiment are combined to build composite spectra of the electron differential fluxes and derive the electron density and pressure. Based on these observations, we provide empirical models of the energy spectrum of the electron flux for different positions. The electron densities and pressures estimated from our composite energy spectra vary from 0.2 cm−3 and 0.1 nPa, respectively, at the center of the current sheet to 0.009 cm−3 and 0.004 nPa, respectively, outside. We compare these observations with those obtained by the Energetic Particles Detector onboard Galileo, which reveal an additional variation of electron fluxes with local time, possibly due to a variation of the current sheet thickness. A similar comparison of magnetic field observations with the latest magnetic field models shows a good agreement. These results can be used for studying the moon‐magnetosphere interactions in preparation for the arrival of the Jupiter Icy Moons Explorer, which will perform multiple flybys of Callisto. Plain Language Summary: The icy moon Callisto orbits within Jupiter's magnetosphere, where it interacts with Jupiter's plasma and magnetic field. This environment varies greatly over the course of the moon's orbit, depending on its distance from the center of the current sheet, a region where much of the Jovian plasma is concentrated. We use data from the last two missions that visited Callisto's orbit to better describe the moon's electron and magnetic environment. By combining data from the two particle detectors aboard Juno, we reconstruct the energy spectrum of the electron differential number flux and infer the electron densities where Callisto orbits. The electron flux and pressure show a variability of a factor of about 20, being maximal at the center of the current sheet and minimal outside. Galileo data reveal an additional variability with local time and lower electron differential number fluxes compared to Juno's observations. Magnetic field data from both missions are compared with several Jovian magnetic field models, and it appears that the models that include the Jovian current sheet are a good approximation at Callisto's orbit. The results are put in the context of the future exploration of Callisto by the Jupiter Icy Moons Explorer in the 2030s. Key Points: We study the variability of electron and magnetic environments at Callisto orbit with local time and M‐shell using Juno and Galileo dataWe provide empirical formulae for electron differential number flux and derive electron parameters at Callisto orbit for different M‐shellsWe show that Jovian magnetic field models are good approximations at Callisto orbit [ABSTRACT FROM AUTHOR]
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Description
Abstract:	Jupiter's moon Callisto orbits in a highly variable magnetospheric environment depending on its position relative to the Jovian current sheet. The Juno and Galileo missions have visited the Jovian magnetosphere and crossed Callisto's orbit several times in a variety of configurations, providing an opportunity to better characterize Callisto's orbital environment. The aim of this work is to characterize the variability of Jupiter's magnetospheric environment properties at Callisto's orbit. After identifying the time intervals during which both missions crossed the moon's orbit, Juno's charged particle data from the Jupiter Energetic Particle Detector Instrument and the Jovian Auroral Distributions Experiment are combined to build composite spectra of the electron differential fluxes and derive the electron density and pressure. Based on these observations, we provide empirical models of the energy spectrum of the electron flux for different positions. The electron densities and pressures estimated from our composite energy spectra vary from 0.2 cm−3 and 0.1 nPa, respectively, at the center of the current sheet to 0.009 cm−3 and 0.004 nPa, respectively, outside. We compare these observations with those obtained by the Energetic Particles Detector onboard Galileo, which reveal an additional variation of electron fluxes with local time, possibly due to a variation of the current sheet thickness. A similar comparison of magnetic field observations with the latest magnetic field models shows a good agreement. These results can be used for studying the moon‐magnetosphere interactions in preparation for the arrival of the Jupiter Icy Moons Explorer, which will perform multiple flybys of Callisto. Plain Language Summary: The icy moon Callisto orbits within Jupiter's magnetosphere, where it interacts with Jupiter's plasma and magnetic field. This environment varies greatly over the course of the moon's orbit, depending on its distance from the center of the current sheet, a region where much of the Jovian plasma is concentrated. We use data from the last two missions that visited Callisto's orbit to better describe the moon's electron and magnetic environment. By combining data from the two particle detectors aboard Juno, we reconstruct the energy spectrum of the electron differential number flux and infer the electron densities where Callisto orbits. The electron flux and pressure show a variability of a factor of about 20, being maximal at the center of the current sheet and minimal outside. Galileo data reveal an additional variability with local time and lower electron differential number fluxes compared to Juno's observations. Magnetic field data from both missions are compared with several Jovian magnetic field models, and it appears that the models that include the Jovian current sheet are a good approximation at Callisto's orbit. The results are put in the context of the future exploration of Callisto by the Jupiter Icy Moons Explorer in the 2030s. Key Points: We study the variability of electron and magnetic environments at Callisto orbit with local time and M‐shell using Juno and Galileo dataWe provide empirical formulae for electron differential number flux and derive electron parameters at Callisto orbit for different M‐shellsWe show that Jovian magnetic field models are good approximations at Callisto orbit [ABSTRACT FROM AUTHOR]
ISSN:	21699380
DOI:	10.1029/2025JA033829