  The origin of Saturn's inner mid-sized moons (Mimas, Enceladus, Tethys, Dione
and Rhea) and Saturn's rings is debated. Charnoz et al. (2010) introduced the
idea 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 initially
massive, and so was the ring's progenitor itself. One may wonder if the
mid-sized moons may have formed also from the debris of a massive ring
progenitor, as also suggested in Canup (2010). However, the process driving
mid-sized moons accretion from the icy debris disks has not been investigated
in details. In particular, this process does not seem able to explain the
varying 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 (a
few times Rhea's mass) and describe the fundamental properties and implications
of this new process. Using a hybrid computer model, we show that accretion
within massive icy rings can form all mid-sized moons from Mimas to Rhea.
However in order to explain their current locations, intense dissipation within
Saturn (with Qp<2000) would be required. Our results are consistent with a
satellite origin tied to the rings formation at least 2.5 Gy ago, both
compatible with either a formation concurrent to Saturn or during the Late
Heavy Bombardment. Tidal heating related to high-eccentricity post-accretional
episodes may induce early geological activity. If some massive irregular chunks
of silicates were initially present within the rings, they would be present
today inside the satellites' cores which would have accreted icy shells while
being tidally expelled from the rings (via a heterogeneous accretion
process)while those still present in the rings are interpreted as today
Saturn's rings' propellers and ring-moons (like Pan or Daphnis).
