The Physics of Planetary Ring Systems

Planetary ring systems are rich astrophysical environments that offer some of the most visually stunning solutions to Newton’s Laws in the solar system. Since the discovery of the Saturnian rings in 1610 by Galileo, planetary rings have been a frequent object of study by both physicists and astronomers. In the past thirty years enhanced earth based equipment and the scientific probes Pioneer-11, Voyager-1, Voyager 2 and Cassini have led to accelerated progress in the field, including the detection of ring systems about the three other gas giants in the Solar System: Neptune, Uranus and Jupiter. This, combined with the many analogies between planetary ring systems and other astrophysical objects such as accretion discs demonstrate a growing need to study such phenomena. In this report we will be interested in the physics of these four ring systems, or more precisely, how physics is able to describe their formation, overall appearance and small scale structure. A thorough investigation must take into account the collective properties of the particles making up these rings and hence delve into the field of fluid dynamics; however, I will for the most part ignore these effects. Rather I will focus on the applications of classical mechanics to these ring systems, which has tremendous power in explaining most of the interesting features observed in the rings.