Morphology of the Auroral Tail of Io, Europa, and Ganymede From JIRAM L‐Band Imager

Alessandro Moirano,Bertrand Bonfond,C Plainaki ,A Migliorini ,R Noschese ,R Sordini ,F Altieri ,G Piccioni ,J R Szalay ,Stavro Ivanovski ,B M Dinelli ,A Cicchetti ,D Turrini ,G Filacchione ,S Massetti ,A Adriani ,R L Lysak ,A Mura ,A H Sulaiman ,J H Waite ,F Tosi ,D Grassi ,Maria Luisa Moriconi ,G Sindoni ,V Dols ,V Hue ,S J Bolton

doi:10.1029/2021ja029450

Abstract

AbstractJupiter hosts intense auroral activity associated with charged particles precipitating into the planet's atmosphere. The Galilean moons orbiting within the magnetosphere are swept by the magnetic field: the resulting perturbation travels along field lines as Alfven waves, which are able to accelerate electrons toward the planet, producing satellite‐induced auroral emissions. These emissions due to the moons, known as footprints, can be detected in various wavelengths (UV, visible, IR) outside the main auroral emission as multiple bright spots followed by footprint tails. Since 2016 the Juno spacecraft orbiting Jupiter has surveyed the polar regions more than 30 times at close distances. Onboard the spacecraft, the Jovian InfraRed Auroral Mapper (JIRAM) is an imager and spectrometer with an L‐band imaging filter suited to observe auroral features at unprecedented spatial resolution. JIRAM revealed a rich substructure in the footprint tails of Io, Europa, and Ganymede, which appear as a trail of quasi‐regularly spaced bright sub‐dots whose intensity fades away along the emission trail as the spatial separation from the footprint increases. The fine structure of the Europa and Ganymede footprint tails is reported in this work for the first time. We will also show that the typical distance between subsequent sub‐dots is the same for all three moons at JIRAM resolution in both hemispheres. In addition, the sub‐dots observed by JIRAM are static in a frame corotating with Jupiter. A feedback mechanism between the ionosphere and the magnetosphere is suggested as a potential candidate to explain the morphology of the footprint tails.

Highlights

Jupiter hosts auroral activities with an intensity significantly greater than Earth and Saturn (Grodent, 2015)
Jovian InfraRed Auroral Mapper (JIRAM) revealed a rich substructure in the footprint tails of Io, Europa, and Ganymede, which appear as a trail of quasiregularly spaced bright sub-dots whose intensity fades away along the emission trail as the spatial separation from the footprint increases
We briefly describe the observations and theoretical works that focus on subcorotation in the plasmasheet close to the Galilean moons: our goal is to provide qualitative support to the hypothesis of ionospheric feedback occurring along the footprint tails without delving into details

Summary

Introduction

Jupiter hosts auroral activities with an intensity significantly greater than Earth and Saturn (Grodent, 2015) Such phenomena are associated with charged particles precipitating into the planetary atmosphere. Jupiter has a strong and extended magnetic field that stretches for about 60–100 RJ in the subsolar direction (RJ = 72,492 km is the Jovian equatorial radius) It is dominated by a plasma whose density in the magnetosphere can be as high as a few thousand particles per cm 3, as reviewed by Thomas et al (2004) and more recently by Bagenal and Dols (2020). As Jupiter's magnetic field rotates faster than the orbit of the Galilean moons, the moons are continuously swept by the Jovian magnetic field and the corotating magnetospheric plasma. This interaction triggers an electromagnetic coupling of the plasma in the magnetosphere with the ionized portion

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Conclusion