Characterisation of Ganymede's ionosphere in the context of future JUICE in situ plasma observations

Previous flybys by NASA missions, namely Galileo and Juno, revealed that Ganymede, the largest moon of the Solar System, hosts a rather complex, dense ionosphere, more diverse than previously thought. Recent modelling work has [1] highlighted that ion-neutral chemistry (e.g. H₂⁺+H₂ ->H₃⁺ + H) occurs and was effective at producing new ion species such as H₃O⁺ and H₃⁺, the latter being detected during Juno flyby. However, these results raise more questions regarding the ability of Juice to characterise Ganymede's ionosphere: 

• Can the different instruments onboard JUICE accurately probe these ion species?
• Can ion species be distinguished and measured within the performance capability of the plasma instruments?

In addition, as ion-neutral collisions appear to be efficient, as evidenced by H₃⁺ detection, another fundamental question arises. Collisions within a plasma affect its conductivity. Depending on its strength, it may affect our ability to characterise the internal structure of Ganymede if not properly constrained.

In this presentation, we propose characterising Ganymede's ionosphere for different configurations, exploring a range of conditions met during the JUICE mission. First, we simulate the ion number densities and ion energy spectra expected to be measured by instruments at JUICE’s location. Secondly, we will estimate Ganymede's ionosphere conductivity for different conditions and assess whether its contribution to the total system is critical.

[1] A Beth, M Galand, X Jia, F Leblanc, Ion-neutral chemistry at icy moons: the case of Ganymede, Monthly Notices of the Royal Astronomical Society, 2025;