  We explore the past evolution of Saturn's moons using direct numerical
integrations. We find that the past Tethys-Dione 3:2 orbital resonance
predicted in standard models likely did not occur, implying that the system is
less evolved than previously thought. On the other hand, the orbital
inclinations of Tethys, Dione and Rhea suggest that the system did cross the
Dione-Rhea 5:3 resonance, which is closely followed by a Tethys-Dione secular
resonance. A clear implication is that either the moons are significantly
younger than the planet, or that their tidal evolution must be extremely slow
(Q > 80,000). As an extremely slow-evolving system is incompatible with intense
tidal heating of Enceladus, we conclude that the moons interior to Titan are
not primordial, and we present a plausible scenario for the system's recent
formation. We propose that the mid-sized moons re-accreted from a disk about
100 Myr ago, during which time Titan acquired its significant orbital
eccentricity. We speculate that this disk has formed through orbital
instability and massive collisions involving the previous generation of
Saturn's mid-sized moons. We identify the solar evection resonance perturbing a
pair of mid-sized moons as the most likely trigger of such an instability. This
scenario implies that most craters on the moons interior to Titan must have
been formed by planetocentric impactors.
