Energetic neutral atoms from Titan: Particle simulations in draped magnetic and electric fields

摘要

Titan's atmosphere emits energetic neutral atoms (ENAs), which are being monitored for the first time by the Cassini spacecraft. These ENAs are generated by charge exchange processes of energetic ions with neutrals from Titan's atmosphere. In this work we investigate the morphology of the ENA emission from Titan's atmosphere with a threedimensional model that calculates the phase space density of the charge exchanging energetic ion population in the vicinity of Titan. With the model ion distribution we calculate the resulting ENA distribution and then generate maps of the ENA emission on a sphere above Titan's atmosphere. We demonstrate that the strongly draped magnetic field lines play an essential role in shaping the ENA morphology. The ENA morphology associated with spatially constant magnetic and electric fields is distinctly different. Observations of ENAs from Titan thus can be used in turn to monitor the electrodynamically complex environment as a whole, which is otherwise only accessible with local measurements along single trajectories.