  Saturn possesses a dynamically rich system containing numerous moons and
impressive rings. Whether the rings of Saturn are much younger than the planet
itself has been a long-open question; more recently a young age has been
proposed for some moons. Recent detection of the fast orbital evolution of Rhea
and Titan strongly suggest a highly frequency-dependent tidal response of
Saturn, possibly through excitation of inertial waves within the planet's
convective envelope. Here we show that the resonance locking to inertial waves
cannot explain the dynamical structure of the Saturnian system or the current
tidal heating of Enceladus. On the other hand, both the observation and our
modelling results indicate that the system is not consistent with evolution
under equilibrium tides. We propose that the system's architecture can best be
explained by relatively high "background" tidal response coupled with discrete
resonant modes. In this view, only Titan may be in a true long-term resonance
lock with a tidal mode of Saturn. Rhea is most likely currently experiencing a
transient period of fast tidal evolution as it passes through a mode, rather
than being locked to it. Assuming that Enceladus went through a temporary
period of fast tidal evolution, we can reproduce its present resonance with
Dione and satisfy other dynamical constraints. Additionally, we conclude that
the long-term tidal response of Saturn to Tethys must be weaker than expected
from frequency-independent tides, as already found by observations.
