A Past Episode of Rapid Tidal Evolution of Enceladus?

By Keith Cowing
Status Report
June 14, 2023
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A Past Episode of Rapid Tidal Evolution of Enceladus?
Simulations of the 2:1 mean-motion resonance crossing between the coorbitals Janus and Epimetheus and Enceladus using simpl. Enceladus and Dione were assumed to be on their current orbits, while Janus and Epimetheus were shifted inward. In the left-hand side panels Janus and Epimetheus were in their current horseshoe configuration, while they were put in a tadpole (Trojan) configuration in the right-hand panels. The coorbitals’ orbits are expanding due to an artificial acceleration meant to represent ring torques. We used k2/Q = 0.01 for Enceladus, and we ignored satellite tides for the coorbitals. — astro-ph.EP

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-open question; more recently a young age has been proposed for some moons.

Recent detection of the fast orbital evolution of Rhea and Titan strongly suggest a highly frequency-dependent tidal response of Saturn, possibly through excitation of inertial waves within the planet’s convective envelope. Here we show that the 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 observation and our modelling 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 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 to 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.

Matija Ćuk, Maryame El Moutamid

Comments: Accepted for PSJ
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2306.07901 [astro-ph.EP] (or arXiv:2306.07901v1 [astro-ph.EP] for this version)
Submission history
From: Matija Cuk
[v1] Tue, 13 Jun 2023 16:52:11 UTC (639 KB)

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