Internal Energy Dissipation in Enceladus's Subsurface Ocean From Tides and Libration and the Role of Inertial Waves. Issue 8 (21st August 2019)

• Record Type: Journal Article
• Authors: Rekier, J.; Trinh, A.; Triana, S. A.; Dehant, V.
• Is Part Of: Journal of geophysical research. Volume 124:Issue 8(2019)
• Page Start: 2198
• Page End: 2212
• Publication Date: 2019-08-21
• Subjects: Planets -- Periodicals; Geophysics -- Periodicals; 559.9
• DOI: 10.1029/2019JE005988
• Languages: English
• ISSNs: 2169-9097

Abstract

Abstract: Enceladus is characterized by a south polar hot spot associated with a large outflow of heat, the source of which remains unclear. We compute the heat generated via viscous dissipation resulting from tidal and (longitudinal) libration forcing in the moon's subsurface ocean using the linearized Navier‐Stokes equation in a three‐dimensional spherical model. We conclude that libration is the dominant cause of dissipation at the linear order, providing up to ∼0.001 GW of heat to the ocean, which remains insufficient to explain the ∼10 GW observed by Cassini. We also illustrate how resonances with inertial modes can significantly augment the dissipation. Our work is an extension to Rovira‐Navarro et al. (2019, https://doi.org/10.1016/j.icarus.2018.11.010 ) to include the effects of libration and the presence of the icy crust. The model developed here is readily applicable to the study of other moons with a subsurface ocean and planets with a liquid core. Plain Language Summary: From the massive amount of information collected by Cassini, Saturn's moon Enceladus currently appears as one of the most habitable moons in the Solar System. Various observations have pointed out the existence of a very active global liquid subsurface water ocean and geysers have also been observed at the moon's south pole indicating a significant amount of geothermal activity. Tidal dissipation is the most likely candidate to explain the heat flux observed at the moon's surface. There is, however, a major discrepancy between the magnitude of the observed heat flux and current estimations from mathematical models. In this work, we focus on the viscous dissipation taking place in the ocean with a special emphasis put on the role played by libration. We have found that libration is the dominant cause of dissipation in the ocean but that it is insufficient to explain the observed heat flux. We also demonstrate how inertial waves (which are waves supported by the Coriolis force) can significantly increase the amount of dissipation via resonance although not sufficiently to challenge the predominance of libration. Key Points: Computation of the viscous dissipation in Enceladus's ocean due to tides and libration Libration‐induced dissipation generates several orders of magnitude more heat than tidal dissipation Inertial mode resonances are related with the excitation of weakly dampened eigenmodes