  The viscous spreading of planetary rings is believed to be counteracted by
satellite torques, either through an individual resonance or through
overlapping resonances. For the A ring of Saturn, it has been commonly believed
that the satellite Janus alone can prevent the ring from spreading via its 7:6
Lindblad resonance. We discuss this common misconception and show that, in
reality, the A ring is confined by the contributions from the group of
satellites Pan, Atlas, Prometheus, Pandora, Janus, Epimetheus, and Mimas, whose
cumulative torques from various resonances gradually decrease the angular
momentum flux transported outward through the ring via density and bending
waves. We further argue that this decrease in angular momentum flux occurs
through 'flux reversal'.
  Furthermore, we use the magnitude of the satellites' resonance torques to
estimate the effective viscosity profile across the A ring, showing that it
decreases with radius from ~50 cm2 s-1 to less than ~10 cm2 s-1. The gradual
estimated decrease of the angular momentum flux and effective viscosity are
roughly consistent with results obtained by balancing the shepherding torques
from Pan and Daphnis with the viscous torque at the edges of the Encke and
Keeler gaps, as well as the edge of the A ring.
  On the other hand, the Mimas 2:1 Lindblad resonance alone seems to be capable
of confining the edge of the B ring, and contrary to the situation in the A
ring, we show that the effective viscosity across the B ring is relatively
constant at ~24-30 cm2 s-1.
