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Tidal interactions between Saturn and its satellites play a crucial role inboth the orbital migration of the satellites and the heating of theirinteriors. Therefore constraining the tidal dissipation of Saturn (here theratio k2/Q) opens the door to the past evolution of the whole system. IfSaturn's tidal ratio can be determined at different frequencies, it may also bepossible to constrain the giant planet's interior structure, which is stilluncertain. Here, we try to determine Saturn's tidal ratio through its currenteffect on the orbits of the main moons, using astrometric data spanning morethan a century. We find an intense tidal dissipation (k2/Q= (2.3 \pm 0.7)\times 10-4), which is about ten times higher than the usual value estimatedfrom theoretical arguments. As a consequence, eccentricity equilibrium forEnceladus can now account for the huge heat emitted from Enceladus' south pole.Moreover, the measured k2/Q is found to be poorly sensitive to the tidalfrequency, on the short frequency interval considered. This suggests thatSaturn's dissipation may not be controlled by turbulent friction in the fluidenvelope as commonly believed. If correct, the large tidal expansion of themoon orbits due to this strong Saturnian dissipation would be inconsistent withthe moon formations 4.5 Byr ago above the synchronous orbit in the Saturniansubnebulae. But it would be compatible with a new model of satellite formationin which the Saturnian satellites formed possibly over longer time scale at theouter edge of the main rings. In an attempt to take into account for possiblesignificant torques exerted by the rings on Mimas, we fitted a constant rateda/dt on Mimas semi-major axis, also. We obtained an unexpected largeacceleration related to a negative value of da/dt= -(15.7 \pm 4.4) \times 10-15au/day.

Strong tidal dissipation in Saturn and constraints on Enceladus' thermal state from astrometry