Resonant Stratification In Titan’s Global Ocean

By Keith Cowing
Status Report
December 11, 2023
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Resonant Stratification In Titan’s Global Ocean
Proposed explanations to Titan’s large k2 as observed by Cassini. The schematic of Titan’s interior model has been extracted from de Kleer et al. (2019). — astro-ph.EP

Titan’s ice shell floats on top of a global ocean revealed by the large tidal Love number k2=0.616±0.067 registered by Cassini. The Cassini observation exceeds the predicted k2 by one order of magnitude in the absence of an ocean, and is 3-σ away from the predicted k2 if the ocean is pure water resting on top of a rigid ocean floor. Previous studies demonstrate that an ocean heavily enriched in salts (salinity S≳200 g/kg) can explain the 3-σ signal in k2.

Here we revisit previous interpretations of Titan’s large k2 using simple physical arguments and propose a new interpretation based on the dynamic tidal response of a stably stratified ocean in resonance with eccentricity tides raised by Saturn. Our models include inertial effects from a full consideration of the Coriolis force and the radial stratification of the ocean, typically neglected or approximated elsewhere.

The stratification of the ocean emerges from a salinity profile where salt concentration linearly increases with depth. We find multiple salinity profiles that lead to the k2 required by Cassini. In contrast with previous interpretations that neglect stratification, resonant stratification reduces the bulk salinity required by observations by an order of magnitude, reaching a salinity for Titan’s ocean that is compatible with that of Earth’s oceans and close to Enceladus’ plumes. Consequently, no special process is required to enrich Titan’s ocean to a high salinity as previously suggested.

Benjamin Idini, Francis Nimmo

Comments: 29 pages, 8 figures, accepted to PSJ
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Fluid Dynamics (physics.flu-dyn)
Cite as: arXiv:2312.05723 [astro-ph.EP] (or arXiv:2312.05723v1 [astro-ph.EP] for this version)
Submission history
From: Benjamin Idini
[v1] Sun, 10 Dec 2023 01:44:49 UTC (5,868 KB)


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