Energetic Proton Dropouts During the Juno Flyby of Europa Strongly Depend on Magnetic Field Perturbations
By Hans Huybrighs (DIAS)
In September 2022 NASA's Juno spacecraft flew by Jupiter's ocean moon Europa. In this study we analyzed energetic ion dropouts measured near Europa. We care about energetic ions because they bombard Europa's icy surface . While they make the surface inhospitable, they might also help produce oxidants from the ice that could form a source of energy for life in the ocean.
The Juno measurements show what happens with the energetic protons at 350 km above the surface, in Europa’s wake (considering the general sense of motion of the protons). There, protons have disappeared, compared to further away where they are abundant. The cartoon below shows some classical ideas about what happens to the protons near Europa (panel 1-2).
Using particle tracing simulations of the ions we can show that the deflections by magnetic fields (3) are also important. In fact, at 100 keV magnetic deflections are the dominant factor that determine the ion abundance. At 1 MeV its a combination of magnetic deflections and the effect shown in panel 2. The simulations also show that the shape of the proton dropout region depends on the exact configuration of the magnetic field, which can vary depending on the atmosphere and electron beams in the wake. All this helps us better understand what happens with the energetic ions and shows us that our ideas of Europa's atmosphere and magnetic fields are reasonable but that improvements can be made.

See publication for details:
, , , , , , et al. (2025). Energetic proton dropouts during the Juno flyby of Europa strongly depend on magnetic field perturbations. Journal of Geophysical Research: Space Physics, 130, e2025JA034000. https://doi.org/10.1029/2025JA034000