Impact of the Core Deformation on the Tidal Heating and Flow in Enceladus' Subsurface Ocean

• Published in: Journal of geophysical research. Planets Vol. 128; no. 11
• Main Authors: Aygün, Burak, Čadek, Ondřej
• Format: Journal Article
• Language: English
• Published: Washington Blackwell Publishing Ltd 01-11-2023
• Subjects: Deformation; Density; Dissipation; Enceladus; Enthalpy; Fluid flow; Freezing; Heat budget; Heating; Ice cover; icy moons; Icy satellites; Jupiter; Ocean circulation; Ocean currents; Ocean models; ocean tides; Oceans; Shallow water; Shallow water equations; South Pole; Thickness; tidal dissipation; Tidal effects; Tidal flow; Viscosity; Water circulation
• ISSN: 2169-9097; 2169-9100
• DOI: 10.1029/2023JE007907

We present a novel approach to modeling the tidal response of icy moons with subsurface oceans. The problem is solved in the time domain and the flow in the ocean is calculated simultaneously with the deformation of the core and the ice shell. To simplify the calculations, we assume that the internal density interfaces are spherical and the effective viscosity of water is equal to or greater than 100 Pa s. The method is used to study the effect of an unconsolidated core on tidal dissipation in Enceladus' ocean. We show that the partitioning of tidal heating between the core and the ocean strongly depends on the thickness of the ocean layer. If the ocean thickness is significantly greater than 1 km, heat production is dominated by tidal dissipation in the core and the amount of heat produced in the ocean is negligible. In contrast, when the ocean thickness is less than about 1 km, tidal heating in the core diminishes and dissipation in the ocean increases, leaving the total heat production unchanged. Extrapolation of our results to realistic conditions indicates that tidal flow is turbulent which suggests that the linearized Navier‐Stokes equation may not be appropriate for modeling the tidal response of icy moons. Finally, we compare our results with those obtained by solving the Laplace tidal equations and discuss the limitations of the two‐dimensional models of ocean circulation.
Plain Language Summary
The origin of the heat powering Enceladus' geological activity and preventing its ocean from freezing has been debated since the discovery of a plume of icy particles above Enceladus' south pole in 2005. Here, we evaluate the heat generated by tides in Enceladus' ocean assuming that the internal density interfaces are spherical and the flow in the ocean is primarily driven by the deformation of Enceladus' unconsolidated core. We find that the heat production in the ocean can explain only a small fraction of Enceladus' heat budget under the present day conditions (i.e., for an ocean thickness of about 40 km) but can be as high as 25 GW if the thickness of the ocean layer is less than about 1 km. Analysis of the flow field suggests that the simplifying assumptions often used in previous studies may not be appropriate. In particular, we show that, regardless of ocean thickness, the dissipation rate obtained by solving the shallow water equations corrected for the dampening effect of the ice shell can be significantly different from that obtained by solving the three‐dimensional Navier‐Stokes equations.
Key Points
The heat production in the ocean depends on the ocean thickness and the material properties of the core
Dissipation is likely to be negligible for ocean thicknesses >1 km but can exceed 20 GW if the ocean is thin and the core is easy to deform
The shallow water approach, widely used in previous studies, can lead to incorrect results regardless of ocean thickness