Juno-UVS observation of the Io footprint during eclipse

The Juno mission offers a unique opportunity to study Jupiter, from its inner structure to its magnetospheric environment. Juno-UVS is a UV spectrograph with a bandpass of 70<lambda<205 mn, designed to characterize Jupiter’s UV emissions. One of the main feature of UVS is its scan mirror, which allows targeting specific UV features that are located +/- 30 ̊ perpendicular to the Juno spin plane. Juno provides a unique vantage point in Jupiter’s system to perform observations otherwise not possible from Earth. During Perijove 3 (PJ time: 11 December 2016 at 17:04 UTC), Io went into eclipse on Dec. 11th from 17:38:43 to 19:52:25 UTC. At that time, Juno was flying over the South Pole and observed the Io footprint from 17:50 to 22:04, with nearly continuous time coverage. Since Juno is spinning at 2 rpm, the Io footprint was observed once every 30 sec. The atmosphere of Io is mostly composed of SO2, with a small contribution of SO, S2, and NaCl. Whether its atmosphere is sublimation driven or supported by the volcanic activity is being controversially debated over decades. Studying the response of Io’s footprint brightness as it enters and leaves eclipse provides a novel method to probe its atmospheric response to a diminution of the solar flux. We will present the observations of this event and how the interaction strength of the interaction between Io’s ionosphere and the magnetosphere of Jupiter evolve during the eclipse.