Wave-particle interactions at the Io and Enceladus flux tubes: A high-resolution, in-situ parametric study

The Juno spacecraft passes through magnetic field lines whose equatorial crossing point is at Io's orbital distance, at least once in each hemisphere around a perijove. Similarly, the Cassini spacecraft crossed those connected to Enceladus' orbits. This enables the first in-situ comparative study between the two systems. The electrodynamic coupling between a dynamic moon and a magnetosphere gives rise to a variety of field and particle phenomena. Here we show evidence of cross-scale wave-particle interactions in Io's flux tube, clearly differentiating between MHD, ion, and electron scales. We find (i) evidence of Alfvén waves undergoing a turbulent cascade, suggesting Alfvénic acceleration processes together with observations of bi-directional, broadband electrons; (ii) intense ion cyclotron waves with an estimated heating rate that is consistent with the generation of observed ion conics; and (iii) whistler-mode auroral hiss radiation excited by field-aligned electrons. Such high-resolution wave and particle measurements provide an insight into satellite interactions in unprecedented detail. We further anticipate that these spatially well-constrained results can be more broadly applied to better understand processes driving Jupiter's main auroral oval. Key similarities and differences are highlighted to measurements of Enceladus' flux tube by Cassini, and we reveal how the power of their interactions compare.