Influence of Titan's Variable Electromagnetic Environment on the Emission of Energetic Neutral Atoms

Abstract:

We model energetic neutral atom (ENA) production at Titan for various moon-magnetosphere configurations and compare their global emission morphologies. Titan's atmosphere is continuously impinged upon by the energetic ion population of Saturn's magnetospheric plasma as it overtakes the moon. Charge exchange interactions between these ions and the neutral atmosphere create ENAs. The emission patterns of these ENAs are sensitive to the draped electromagnetic field configuration near the moon, allowing for a global picture of Titan's complex interaction with Saturn's magnetosphere to be captured through ENA imaging. In this work, we compute the trajectories of upstream energetic ions and model the production of ENAs in Titan's atmosphere in order to generate global flux maps of ENA emissions for various positions of Titan with respect to Saturn's magnetic equator. In order to capture the full dynamics of the energetic ions, which have gyroradii comparable to the radius of Titan, we trace particle trajectories through fields from a hybrid (kinetic ions, fluid electrons) model of the moon-magnetosphere interaction. We compare the global ENA emissions at Titan when it is located in the magnetodisk current sheet and at various locations in the southern magnetodisk lobe. As a baseline, we also examine emissions under uniform field conditions. ENA emissions are shown to be sensitive to changes in the configuration of the draped fields that result from Titan's interaction with Saturn's magnetic field. This suggests that ENA imaging may be useful more generally for obtaining a global, qualitative picture of dynamic moon-magnetosphere interactions. In preparation for the upcoming JUICE mission, we therefore examine the applicability of our model to the Jovian moons Callisto and Europa.