Speaker
Description
The Io plasma torus offers our only opportunity to take a picture of a planetary magnetosphere. Torus ion emissions are excited through electron impact and so line ratios of like ions species can effectively map the plasma density and electron temperature. This provides us with some empirical constraints on the upstream plasma conditions that sweep past the moon. A rich spectrum of emission features is seen local to Io because of its interaction with the torus, and dozens of transitions in Io’s atmosphere are not observable anywhere else. Photochemical and plasma-induced channels emissions can be disentangled by comparing telescope spectra in sunlight to eclipsed spectra in Jupiter’s shadow. The vapor pressure equilibrium of Io’s bulk SO2 atmosphere is tipped out of balance during Io’s ingress and egress. Comparing the temporal response of SO2 to Io’s atomic emissions reveals important new clues on the production pathways for the atoms, as well as the complex factors that regulate their photon flux. Plasma induced atomic lines are confluence of several processes including direct excitation of the atoms, dissociative excitation of molecules, recombination reactions in Io’s ionosphere, and, in the case of forbidden transitions, collisional quenching. Sunlight and electron impacts can also ionize, and any ions created in collisionless regions of Io’s atmosphere are ripped out by Jupiter’s magnetic field. This ion population not only re-supplies the torus, causing feedback, it can also dissociatively recombine or charge exchange to form streams of energetic neutral atoms. Doppler shift can distinguish such neutrals borne of ionic parents. With velocities well above the jovian escape speed, these energetic neutral atoms can paint the surfaces of the other satellites or populate Jupiter’s diffuse and dynamic nebulae as one of the largest structures in our solar system.
