Tidal dissipation in Enceladus' uneven, fractured ice shell

Souček, Ondřej; Běhounková, M.; Čadek, O.; Hron, J.; Tobie, G.; Choblet, G.

doi:10.1016/j.icarus.2019.02.012

Cited by 46 publications

(77 citation statements)

References 61 publications

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“…The shell power for nominal values of viscoelastic parameters is only a few percent of the conductive power, in agreement with Souček et al [2019]. If the shell dissipation rate is ten times higher, as suggested by recent laboratory experiments, it contributes to nearly half the conductive power and accounts for most of the spatial variations of the conductive flux.…”

Section: Discussionsupporting

confidence: 87%

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Enceladus's crust as a non-uniform thin shell: II tidal dissipation

Beuthe

2019

Icarus

103

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Tidal heating is the prime suspect behind Enceladus's south polar heating anomaly and global subsurface ocean. No model of internal tidal dissipation, however, can explain at the same time the total heat budget and the focusing of the energy at the south pole. I study here whether the non-uniform icy shell thickness can cause the north-south heating asymmetry by redistributing tidal heating either in the shell or in the core. Starting from the non-uniform tidal thin shell equations, I compute the volumetric rate, surface flux, and total power generated by tidal dissipation in shell and core. The micro approach is supplemented by a macro approach providing an independent determination of the core-shell partition of the total power. Unless the shell is incompressible, the assumption of a uniform Poisson's ratio implies non-zero bulk dissipation. If the shell is laterally uniform, the thin shell approach predicts shell dissipation with a few percent error while the error on core dissipation is negligible. Variations in shell thickness strongly increase the shell dissipation flux where the shell is thinner. For a hard shell with long-wavelength variations, the shell dissipation flux can be predicted by scaling with the inverse local thickness the flux for a laterally uniform shell. If Enceladus's shell is in conductive thermal equilibrium with isostatic thickness variations, the nominal shell dissipation flux at the south pole is about three times its value for a shell of uniform thickness, which remains negligible compared to the observed flux. The shell dissipation rate should be ten times higher than nominal in order to account for the spatial variations of the observed flux. Dissipation in an unconsolidated core can provide the missing power, but does not generate any significant heating asymmetry as long as the core is homogeneous. Non-steady state models, though not investigated here, face similar difficulties in explaining the asymmetries of tidal heating and shell thickness.

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Section: Discussionsupporting

confidence: 87%

“…low) dissipation, the shell dissipation flux is only a few percent of the conductive flux (Fig. 11B), as found by Souček et al [2019]. While the non-uniformity of the shell only slightly increases the shell power (by 20%, see Table 6), it has a major effect on the pattern of the shell dissipation flux.…”

Section: Shell Dissipationsupporting

confidence: 64%

Enceladus's crust as a non-uniform thin shell: II tidal dissipation

Beuthe

2019

Icarus

103

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“…The main fractures of Enceladus are the Tiger Stripe Fractures (TSF), which are located in the South Polar Terrain (SPT) and are sites of plume eruptions (Figure 1; Crow‐Willard & Pappalardo, 2015; C. C. Porco et al., 2006). The TSF and other fractures which are surrounded by a peripheral chain of ridges and valleys characterize the SPT region (Figure 1) and represent weakness zones and potential connections between the surface and underlying ocean (Lucchetti et al., 2017; Souček et al., 2019).…”

Section: Introductionmentioning

confidence: 99%

“…represent weakness zones and potential connections between the surface and underlying ocean (Lucchetti et al, 2017;Souček et al, 2019).…”

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confidence: 99%

Tectonics of Enceladus’ South Pole: Block Rotation of the Tiger Stripes

et al. 2020

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Observations of water vapor and ice-crystal plumes emanating from the south polar region of Enceladus are among the most striking discoveries of the Cassini-Huygens Mission (e.g., Hansen et al., 2006; C. C. Porco et al., 2006; Spencer et al., 2006). This plume activity is associated with tectonically and thermally active terrains, witnessing strong interactions with the interior dynamics. Both chemical and geophysical measurements performed by the Cassini spacecraft imply that this activity is most likely related to the existence of a liquid salty layer at relatively shallow depth underneath the icy crust at the south pole which is possibly associated with hydrothermal activity at the seafloor (

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“…In comparison with more standard rheologies, it can significantly affect the probability of capture in spin-orbit resonance and/or amplify the amount of dissipated energy (Makarov and Efroimsky, 2013;Leconte et al, 2015;Makarov, 2015;Makarov et al, 2016;Walterová and Běhounková, 2017;Renaud and Henning, 2018). The Andrade rheology has been applied in studies of specific celestial bodies such as the Moon (Nimmo et al, 2012;Williams et al, 2014;Williams and Boggs, 2015), Mercury (Padovan et al, 2014;Noyelles et al, 2014;Knibbe and van Westrenen, 2017), Enceladus (Rambaux et al, 2010;Shoji et al, 2013;Běhounková et al, 2013Běhounková et al, , 2015Souček et al, 2019), Iapetus , Io (Bierson and Nimmo, 2016), binary asteroids (Efroimsky, 2015), GJ581 d (Makarov et al, 2012), and Proxima Century b (Ribas et al, 2016).…”

Section: Introductionmentioning

confidence: 99%

Andrade rheology in time-domain. Application to Enceladus' dissipation of energy due to forced libration

Gevorgyan

Boué

Ragazzo

et al. 2020

Icarus

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The main purpose of this work is to present a time-domain implementation of the Andrade rheology, instead of the traditional expansion in terms of a Fourier series of the tidal potential. This approach can be used in any fully three dimensional numerical simulation of the dynamics of a system of many deformable bodies. In particular, it allows large eccentricities, large mutual inclinations, and it is not limited to quasi-periodic perturbations. It can take into account an extended class of perturbations, such as chaotic motions, transient events, and resonant librations.The results are presented by means of a concrete application: the analysis of the libration of Enceladus. This is done by means of both analytic formulas in the frequency domain and direct numerical simulations. We do not a priori assume that Enceladus has a triaxial shape, the eventual triaxiality is a consequence of the satellite motion and its rheology. As a result we obtain an analytic formula for the amplitude of libration that incorporates a new correction due to the rheology.Our results provide an estimation of the amplitude of libration of the core of Enceladus as 0.6% of that of the shell. They also reproduce the observed 10 GW of tidal heat generated by Enceladus with a value of 0.17 × 10 14 Pa·s for the global effective viscosity under both Maxwell and Andrade rheology.

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Tidal dissipation in Enceladus' uneven, fractured ice shell

Cited by 46 publications

References 61 publications

Enceladus's crust as a non-uniform thin shell: II tidal dissipation

Enceladus's crust as a non-uniform thin shell: II tidal dissipation

Tectonics of Enceladus’ South Pole: Block Rotation of the Tiger Stripes

Andrade rheology in time-domain. Application to Enceladus' dissipation of energy due to forced libration

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