A Past Episode of Rapid Tidal Evolution of Enceladus?

Abstract

Saturn possesses a dynamically rich system containing numerous moons and impressive rings. Whether the rings of Saturn are much younger than the planet itself has been a long-standing open question; more recently a young age has been proposed for some moons. The recent detection of the fast orbital evolution of Rhea and Titan strongly suggests a highly frequency-dependent tidal response of Saturn, possibly through the excitation of inertial waves within the planet’s convective envelope. Here we show that resonance locking to inertial waves cannot explain the dynamical structure of the Saturnian system or the current tidal heating of Enceladus. On the other hand, both the observations and our modeling results indicate that the system is not consistent with evolution under equilibrium tides. We propose that the system’s architecture can best be explained by a relatively high “background” tidal response coupled with discrete resonant modes. In this view, only Titan may be in a true long-term resonance lock with a tidal mode of Saturn. Rhea is most likely currently experiencing a transient period of fast tidal evolution as it passes through a mode, rather than being locked into it. Assuming that Enceladus went through a temporary period of fast tidal evolution, we can reproduce its present resonance with Dione and satisfy other dynamical constraints. Additionally, we conclude that the long-term tidal response of Saturn to Tethys must be weaker than expected from frequency-independent tides, as already found by observations.

Quantifying Uncertainty in Sustainable Biomass and Production of Biotic Carbon in Enceladus' Notional Methanogenic Biosphere

“…(2021) concluded that hydrogenotrophic methanogenesis still appears to be the metabolism with the highest energy yield and biomass potential. If Enceladus is younger than once thought (Ćuk & Moutamid, 2023; Ćuk et al., 2016; though see also Nimmo et al., 2023) and/or life is in the early stages of evolution, metabolic inefficiencies may explain some of the high Gibbs free energies inferred. Finally, spatial constraints (e.g., restricted space for a habitat on the seafloor) could limit access to H 2 despite it being readily available in solution, particularly if the ocean plume is rotationally controlled and spatially isolated to a column during transit to the ice layer (e.g., Choblet et al., 2017; Schoenfeld et al., 2023), though wider mixing of seawater with HF and longer timescales of vertical transport have been proposed (e.g., Kang et al., 2022).…”

Origin and Evolution of Enceladus’s Tidal Dissipation

“…Further discussion on the orbital constraints may be found in the articles by Ćuk et al. ( this collection ) and the paper by Ćuk and El Moutamid ( 2023 ).…”

“… 2018 ; Lainey et al. 2020 ; Ćuk and El Moutamid 2023 ), including the article by Fuller et al. ( this collection ).…”

“…Unfortunately, for the Enceladus-Dione case, and so whether direct tidal torques on Dione ( ) are important matters a great deal, both for deriving and for determining the equilibrium heat flow (equation ( 4 )). These issues are also discussed in Ćuk and El Moutamid ( 2023 ).…”

Strong Tidal Dissipation at Uranus?

“…Second, the Q of Uranus at the time of tidal heating may have been a short-lived phenomenon and not representative of the longer-term value. One way of achieving this effect, which was recently suggested for Rhea and Enceladus by Ćuk & El Moutamid (2023), is to have the satellite pass through a resonant mode with the planet but not get locked to that resonance. To be effective in driving tidal heating, the satellite would have to have been in an MMR at the time of modecrossing.…”