Tidal Dissipation in the Saturnian System

In our development of the Saturnian satellite ephemerides to support the Cassini tour of the Saturnian system we did not take into account tidal forces. However, Lainey et al. (2012 Astrophys. J. 752, 14), Polycarpe et al. (2018 A&A 619, A133), and Lainey et al. (2020 Nature Astron. 4, 1053) have published investigations of tidal effects in the Saturnian system. Consequently, for our post-Cassini ephemeris work in preparation for the future Dragonfly mission to Titan we decided to include the effects of tides raised on the planet by the six innermost major satellites (Hyperion and Iapetus are too distant to be strongly influenced by tides). We also included the tide raised on Enceladus by Saturn because its effects are of interest in the thermal and orbital evolution of that satellite (Nimmo et al., 2018 in Enceladus and the Icy Moons of Saturn, Schenk et al. Eds., Univ. Arizona Press). In this paper we describe our model for the tidal forces and report the values of the tidal quality factors, Q, determined in the course of our ephemeris development. Because planets and satellites are not perfectly elastic, the friction within them produces a time delay in the raising of a tidal bulge on them and causes energy dissipation within them. The quality factor is a measure of that dissipation. We compare our tidally accelerated satellite orbits with those used for the final reconstruction of the Cassini tour. We find that five of the six satellites are spiraling out from Saturn as a consequence of the acceleration caused by the tidal bulge raised on Saturn. But Enceladus is spiraling inward as the tide raised on it by Saturn overwhelms the tide raised by it on Saturn.