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Ganymedes atmosphere is one of the most complex among the moons of our solar system. As the only known satellite in our solar system to feature an intrinsic global magnetic field, Ganymede forms a small magnetosphere within the much larger magnetosphere of Jupiter. The interaction between the two magnetospheres makes Ganymede's plasma environment highly variable both in space and time. Consequently, the moon's atmosphere, predominantly shaped by the interplay between the plasma environment and Ganymede's surface, likely exhibits a corresponding high degree of variability. The recent Juno spacecraft flyby of Ganymede has provided us with unprecedented insights into the moon's electron and ion environment. This study capitalizes on electron data collected by the Jovian Auroral Distributions Experiment (JADE) during Juno's traversal of Ganymede's magnetopause current layer, employing these measurements as a proxy for the electron conditions within Ganymede's auroral region. Our simulations reveal that these electrons play a pivotal role in governing Ganymede's H2 and O2 atmospheres, representing the predominant constituents of its atmospheric composition. Furthermore, the abundance of atomic O and H, crucial factors in Ganymede's atmospheric mass loss, is intricately influenced by these electrons, underscoring their significance in shaping the complex dynamics of Ganymede's atmospheric behavior. Our current understanding of Ganymede's atmosphere predominantly stems from spectroscopic observations. However, it's crucial to acknowledge that the interpretation of spectroscopic data heavily relies on certain assumptions. Our analysis underscores the significance of acquiring a comprehensive understanding of Ganymede's atmosphere. To achieve this, it is imperative to conduct simultaneous observations encompassing the moon's surface, its atmospheric conditions, and the entirety of its plasma environment, including both thermal and energetic ions and electrons.
Vorburger et al. (Fri,) studied this question.