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The origin of Saturn's inner mid-sized moons (Mimas, Enceladus, Tethys, Dioneand Rhea) and Saturn's rings is debated. Charnoz et al. (2010) introduced theidea that the smallest inner moons could form from the spreading of the rings'edge while Salmon et al. (2010) showed that the rings could have been initiallymassive, and so was the ring's progenitor itself. One may wonder if themid-sized moons may have formed also from the debris of a massive ringprogenitor, as also suggested in Canup (2010). However, the process drivingmid-sized moons accretion from the icy debris disks has not been investigatedin details. In particular, this process does not seem able to explain thevarying silicate contents of the mid-sized moons (from 6% to 57% in mass).Here, we explore the formation of large objects from a massive ice-rich ring (afew times Rhea's mass) and describe the fundamental properties and implicationsof this new process. Using a hybrid computer model, we show that accretionwithin massive icy rings can form all mid-sized moons from Mimas to Rhea.However in order to explain their current locations, intense dissipation withinSaturn (with Qp<2000) would be required. Our results are consistent with asatellite origin tied to the rings formation at least 2.5 Gy ago, bothcompatible with either a formation concurrent to Saturn or during the LateHeavy Bombardment. Tidal heating related to high-eccentricity post-accretionalepisodes may induce early geological activity. If some massive irregular chunksof silicates were initially present within the rings, they would be presenttoday inside the satellites' cores which would have accreted icy shells whilebeing tidally expelled from the rings (via a heterogeneous accretionprocess)while those still present in the rings are interpreted as todaySaturn's rings' propellers and ring-moons (like Pan or Daphnis).

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Accretion of Saturn's mid-sized moons during the viscous spreading of  young massive rings: solving the paradox of silicate-poor rings versus  silicate-rich moons