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Tidal heating in Io’s magma ocean

Presentation #111.02 in the session Io (Poster)

Published onOct 23, 2023
Tidal heating in Io’s magma ocean

Io’s volcanic activity is driven by the heat generated by tidal friction caused by its orbital resonance with Europa and Ganymede. Dissipation of tidal energy can occur in both the solid and liquid regions of the satellite. In a solid material, the dissipative properties depend on the composition, temperature and structural characteristics (grain size, melt content, etc.), while the dissipation in a liquid is controlled by a single parameter, viscosity, varying with temperature and composition. Physical models of solid body tides on Io usually assume that most of the heat is generated in a partially molten layer (a “magma sponge”) beneath Io’s lithosphere or in a deeper, potentially dissipative mantle. Alternatively, tidal heating can be concentrated in a hypothetical magma ocean which is approximated by a fluid layer. The main difference between the solid and fluid tides is that the tidal deformation of a fluid layer is affected by the Coriolis force, an effect which is negligible in solid tide models. Here, we investigate tidal dissipation in a 0.2–10 km thick fluid layer located on top of a magma sponge (cf., Miyazaki and Stevenson, Planet. Sci. J., 2022). Unlike the study by Tyler et al. (Astrophys. J. Suppl., 2015) where the flow in the ocean was described as a barotropic two-dimensional sheet flow (i.e., by the Laplace tidal equations), we solve the three-dimensional Navier-Stokes equations and take into account the mechanical coupling between the ocean and the solid parts of the mantle. We find that the tidal flow produces a wide variety of heating patterns and even small changes in ocean thickness can lead to order of magnitude changes in the total heat production. The highest heat production (more than ten thousand TW) is found in the case where tidal heating is concentrated in an equatorial zone at latitudes below 30 degrees. This equatorial zone is clearly separated from the non-dissipative regions at higher latitudes and its position shows a remarkable correspondence with Io’s yellow bright plains. Our results indicate that depending on the thickness of the magma ocean, Io experiences periods of enhanced heat production which can significantly alter its surface.

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