  Io is the most volcanically active body in the Solar System. This volcanic
activity results in the ejection of material into Io's atmosphere, which may
then escape from the atmosphere to form various structures in the jovian
magnetosphere, including the plasma torus and clouds of neutral particles. The
physical processes involved in the escape of particles - for example, how the
volcanoes of Io provide material to the plasma torus - are not yet fully
understood. In particular, it is not clear to what extent the sodium jet, one
of the sodium neutral clouds related to Io, is a proxy of processes that
populate the various reservoirs of plasma in Jupiter's magnetosphere. Here, we
report on observations carried out over 17 nights in 2014-2015, 30 nights in
2021, and 23 nights in 2022-2023 with the TRAPPIST telescopes, in which
particular attention was paid to the sodium jet and the quantification of their
physical properties (length, brightness). It was found that these properties
can vary greatly from one jet to another and independently of the position of
Io in its orbit. No clear link was found between the presence of jets and
global brightening of the plasma torus and extended sodium nebula, indicating
that jets do not contribute straightforwardly to their population. This work
also demonstrates the advantage of regular and long-term monitoring to
understanding the variability of the sodium jet and presents a large corpus of
jet detections against which work in related fields may compare.
