Quantifying the Stress of the Saturnian Magnetosphere During the Cassini Era

We quantify the magnetospheric stress state of Saturn, revealing the nature of the planetary environment and its current systems. The complete magnetic field data set collected by the Cassini spacecraft is used to track the global behavior of the Saturnian magnetosphere during the Cassini era. Variations in the magnetodisc current model parameter mu I-o(o) determine when the system is stretched, compressed, or near the ground state. Of the 111 orbits that pass through our chosen region, 69 are well described by the model, indicating a steady state current sheet during this interval. While the stress state displays a dependence on local time, it is also shown to vary temporally. We conclude that the Saturnian magnetosphere remained in a quiet state for a significant period of the Cassini orbital mission at Saturn, with occasional large-scale deviations observed. Plain Language Summary The Cassini spacecraft orbited the planet Saturn for 13 years before plummeting into its atmosphere in September 2017. The mission provided a rich data set that was collected by the onboard instruments, uncovering many characteristics of the planetary environment. Now the mission is complete, we have a unique opportunity to quantify this behavior over a significant period of time. This work will use the complete magnetometer data set to track the size of the magnetic environment that surrounds Saturn, called its magnetosphere. Due to processes both within and outside of this cavity, the size of the magnetosphere changes constantly. The question that this analysis will answer is whether this change is steady over this extended interval, which amounts to almost half a Saturn year. Our results show that the size of the magnetosphere did not vary for a significant duration of this era but that large-scale changes were observed, where the field was sufficiently stretched or compressed. This has implications for the broader study of giant magnetospheres, which are found both within and outside of our solar system. These results also reveal how dynamic the magnetosphere of Saturn is compared to the magnetosphere of Earth, improving our understanding of the terrestrial environment.