Emission of Energetic Neutral Atoms at Callisto and Europa

Based on a combination of hybrid simulations and energetic particle tracing, we model the emission morphology of energetic neutral atoms (ENAs) that are generated by the interaction of the atmospheres around Callisto and Europa with energetic ions from Jupiter's magnetosphere. Since the trajectories of the energetic parent ions are strongly affected by the local electromagnetic field perturbations near Callisto and Europa, the ENA emission morphology contains an admixture of information on the particle distribution functions and the draped magnetic field configurations near both moons. Thus, the ENA emission pattern can be regarded as a snapshot of the moons' plasma interaction regions on a global scale. We apply the hybrid code to compute the three-dimensional structure of Callisto's and Europa's electromagnetic environments. By tracing the motion of several billions of energetic parent ions and their interaction with the moons' atmospheres, we then compute maps of the ENA flux through a concentric sphere around each moon. To isolate the influence of the draped fields near both moons, these ENA emission maps will be compared against the modeled emission patterns for homogeneous electromagnetic fields. The results allow to constrain the diagnostic potential of ENA images to characterize the moons' perturbed electromagnetic environments as a whole, in addition to local plasma and magnetic field observations along a spacecraft trajectory.