Study of the sodium jet of Io with the TRAPPIST telescopes

Io is the solar system’s most volcanically active body. This volcanic activity results in the ejection of material into Io’s atmosphere, which 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 bright D-doublet of sodium, could help solve the mystery surrounding the escape of those particles. Here we report on observations carried out during 15 nights in 2014 and 2015 with the 60 cm robotic TRAPPIST-South telescope and a narrow band sodium filter. On those images, a particular attention was paid on the sodium jet, one of the neutral sodium features. Among the images where the jet can be seen, we noticed that it does not always have the same size and brightness from one observation to another. The current study is to measure the physical quantities, as the brightness of the jet, its length and duration to be able to quantify these variations through time.
Furthermore, similar Io sodium observations are currently planned and carried out with both TRAPPIST telescopes. The images will be processed via different methods to highlight the sodium jets. Contrary to the observations made in 2014 and 2015, the new observations will be performed at moments chosen specifically to observe the jet. The configuration of Io with respect to Jupiter will be more or less the same from one observation to another in order to facilitate the comparisons. These new observations will be in the form of a monitoring, about two times a week for several months, to maximize the chances to catch the jet and have a more continuous data set to have a better understanding of its variation through time. In case a bright event is detected, more and dense observations will be carried for several hours continuously to follow the event.