Overview of Io torus monitoring by Juno. The position of the Io footprint is observed by the Jovian Infrared Auroral Mapper (red field of view) and/or the Ultraviolet Spectrograph (blue field of view) as the spacecraft passes over the polar regions. The lead angle (gray arrow) represents the angular difference between the Io footprint’s longitude, mapped at Io’s orbit using the magnetic field (black dashed line), and Io’s longitude at the same epoch. The lead angle encapsulates information about the tilt of the Alfvén wing (purple line; see Section 3) relative to the magnetic field, and thus about the condition of the torus. Between polar overflights, Juno frequently performs radio occultation of the Io torus (green line), conducted by the Ka-band Translator System and Small Deep Space Transponder of the Gravity experiment onboard the spacecraft. The path delay measured by the Deep Space Station (plot on the right) shows a pronounced signature caused by the electron content of the Io torus as Juno passes behind it.