Analysis of the sodium jets detected on Io with TRAPPIST

Io is the solar system’s most volcanically active body. This volcanic activity results in the ejection of material into Io’s atmosphere. This material then escapes from the atmosphere to form various structures in the Jovian magnetosphere. These include the plasma torus and clouds of neutral particles. The physical processes involved in the escape of particles are not yet fully understood. Indeed, the study of the atmosphere and the volcanoes in the one hand and the study of the plasma torus on the other hand, lead to two different conclusions regarding the origin of the variability of the torus plasma content. Observations of Io, with a particular focus on the neutral sodium clouds, which are
relatively easy to detect thanks to the D-doublet of sodium, could help solve the mystery surrounding the escape of those particles.
Observations with the TRAPPIST telescopes and their sodium filter have been carried out during 17 nights from December 2014 to April 2015 and 30 nights from April to October 2021. On those images, a particular attention was paid on the sodium jet, one of the neutral sodium clouds. The images from those two periods have been processed to highlight the presence of sodium in order to determine the presence or not of the sodium jet. From the 17 nights of the 2014-2015 period, the sodium jet has appeared for four nights, and it as appeared for three nights for the 2021 period. Among the images
where the jet can be seen, it is visible that it does not always have the same size and brightness from one observation to another. The current goal is to establish the physical quantities, as the brightness, the size and the orientation of the jet that are observed. So far it can be established that the jet variation does not, or not only, depend on the phase angle of Io.
Moreover, we will show early results from a model of the plasma torus aimed at characterizing the influence of the variation of the sodium jet on it.