The magnetosphere of Saturn

Abstract

The Pioneer 11, Voyagers 1 and 2 encounters with Saturn provided a wealth of information about its complex magnetosphere. The magnetic dipole moment of Saturn is rotationally aligned and only one‐fifth of that expected from pre‐encounter modeling. The bow shock stand‐off distance is about 22 RS and varies with solar wind pressure proportional to p−1/6. The satellites Titan, Dione, and Tethys are probably the primary sources of magnetospheric plasma. For <10 keV thermal plasma, β is less than one in most of the magnetosphere, but contributions from ∼20 keV plasma may increase this value significantly. Outside of ∼4 RS, energetic particles are energized by diffusing inward while conserving their first and second adiabatic invariants. Particles are lost by satellite sweep‐out, absorption by the E ring and probably also by plasma interactions, which produce a slot region between 4 and 9 RS. The inner magnetosphere is characterized by a cold plasma population (<10 eV/charge), which probably consists primarily of 0+ and has a scale height from the Equator of only 0.2 RS. Intense penetrating radiation exists in the inner magnetosphere from 4 RS to 2.265 RS, which coincides with the outer edge of the A ring. The energetic protons ⩾50 MeV have approximately the spectrum expected from a cosmic ray albedo neutron decay source. A proton component below 0.5 MeV was also found, as well as an electron flux with energies primarily above 1.5 MeV. Submicron charged dust gains constitute a new type of magnetospheric particle and their properties may explain the evolution of the B ring spokes and other B ring features.