Properties of Electrons Accelerated by the Ganymede-magnetosphere Interaction: Survey of Juno High-latitude Observations

By Keith Cowing
Status Report
May 7, 2024
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Properties of Electrons Accelerated by the Ganymede-magnetosphere Interaction: Survey of Juno High-latitude Observations
JADE in situ and UVS remote observations made during PJ16N. (a) UV false color image of the auroral emissions observed close to Ganymede’s footprint. The Juno footpath and the instantaneous footprints of the Galilean moons derived using the JRM33+CON2020 models are shown as red lines and orange dots, respectively. The boundary of the time window over which the UVS data has been co-added is shown at the bottom right corner, and is reported on the Juno footpath as two red dots. The white triangles and crosses along the Juno footpath highlight Juno’s instantaneous footprints with a 10 and 2 minutes time step, respectively. (b) Electron differential number flux measured by JADE-E. The EF is superimposed. (c) Pitch angle distribution. The size of the loss cones at the time of the flux tube crossing is indicated by the dashed line. (d) Arbitrary brightness related to the number of UVS total countrate, UVS false color along the footpath of Juno and electron characteristic energy. The information related to the position of Juno are indicated below the panel (d). The times for the flux tubes crossings estimated from JRM33+CON2020 are represented by vertical gray lines in panels (b, c, d). Events associated with a Ganymede’s flux tube crossing are highlighted by an orange rectangle while the crossing of the main oval is displayed, in panels (b, c, d), as a purple rectangle. — astro-ph.EP

The encounter between the Jovian co-rotating plasma and Ganymede gives rise to electromagnetic waves that propagate along the magnetic field lines and accelerate particles by resonant or non-resonant wave-particle interaction. They ultimately precipitate into Jupiter’s atmosphere and trigger auroral emissions.

In this study, we use Juno/JADE, Juno/UVS data, and magnetic field line tracing to characterize the properties of electrons accelerated by the Ganymede-magnetosphere interaction in the far-field region. We show that the precipitating energy flux exhibits an exponential decay as a function of downtail distance from the moon, with an e-folding value of 29°, consistent with previous UV observations from the Hubble Space Telescope (HST). We characterize the electron energy distributions and show that two distributions exist.

Electrons creating the Main Alfvén Wing (MAW) spot and the auroral tail always have broadband distribution and a mean characteristic energy of 2.2 keV while in the region connected to the Transhemispheric Electron Beam (TEB) spot the electrons are distributed non-monotonically, with a higher characteristic energy above 10 keV. Based on the observation of bidirectional electron beams, we suggest that Juno was located within the acceleration region during the 11 observations reported.

We thus estimate that the acceleration region is extended, at least, between an altitude of 0.5 and 1.3 Jupiter radius above the 1-bar surface. Finally, we estimate the size of the interaction region in the Ganymede orbital plane using far-field measurements. These observations provide important insights for the study of particle acceleration processes involved in moon-magnetosphere interactions.

J. Rabia, V. Hue, N. Andre, Q. Nenon, J.R. Szalay, F. Allegrini, A.H. Sulaiman, C.K. Louis, T.K. Greathouse, Y. Sarkango, D. Santos-Costa, M. Blanc, E. Penou, P. Louarn, R.W. Ebert, G.R. Gladstone, A. Mura, J.E.P. Connerney, S.J. Bolton

Comments: Accepted for publication in JGR: Space Physics
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2405.02382 [astro-ph.EP] (or arXiv:2405.02382v1 [astro-ph.EP] for this version)
Submission history
From: Jonas Rabia
[v1] Fri, 3 May 2024 15:19:48 UTC (5,997 KB)

Explorers Club Fellow, ex-NASA Space Station Payload manager/space biologist, Away Teams, Journalist, Lapsed climber, Synaesthete, Na’Vi-Jedi-Freman-Buddhist-mix, ASL, Devon Island and Everest Base Camp veteran, (he/him) 🖖🏻