The Ring Current of Saturn

Saturn is a rapidly rotating planet with a relatively strong intrinsic magnetic field and significant internal plasma sources, that produce the required internal pressure to deflect the solar wind and form a large magnetosphere, which holds a complex and dynamic electric current system. A very important part of this global system is a current carried by magnetospheric charged particles flowing near the equatorial plane, in the azimuthal direction around the planet at radial distances between similar to 8 R-s and similar to 15 R-s, and is often referred to as the "ring current." As in most magnetized planets, the ring current plays a key role in the magnetosphere-ionosphere coupling at Saturn. In particular, its azimuthal asymmetry is associated with the generation and topology of the field-aligned currents, which are believed to affect, or to some extent drive, the periodic variability that has been well observed in several magnetospheric properties but is not fully understood. In this chapter, we provide an up-to-date overview of the Kronian ring current, including the most recent advances. Following a brief historical review, the chapter focuses on results from the Cassini spacecraft, which spent over 13 yr in orbit around the planet (2004-2017) and returned a large volume of observational data, which have not been fully exploited yet. The text summarizes results that have been published over the last decades, and is organized in three subsections that cover complementary approaches on the subject: in situ observations, remote imaging, and modeling.