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

Abstract

Jupiter 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.