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The Cassini mission provided unprecedented insights into the Kronian system and revealed many unexpected phenomena relating to dusty plasma environments around Saturn and its rings. Almost 13 years after its arrival, Cassini began a series of 22 orbits which brought it between Saturn's upper atmosphere and the innermost D ring, culminating in a final plunge into Saturn's ionosphere. This concluding period of Cassini's journey is referred to as the Grand Finale and data collected during these final orbits serves as the foundation for the two papers included in this thesis.

We constrain the composition of positive ions in Saturn's equatorial ionosphere by deriving upper limits for the effective recombination coefficient. Our results suggest an ionosphere dominated by species with low recombination coefficients, such as HCO⁺. The analysis of Grand Finale data further revealed small-scale variations in the H₂⁺ density for two of the orbits. We link these to narrow substructures in Saturn's C ring with increased optical depths, which attenuate the solar extreme ultraviolet flux and thus reduce photoionisation rates within their respective shadowed regions.