Coupled convection and tidal dissipation in Europa’s ice shell using non-Newtonian grain-size-sensitive (GSS) creep rheology

Han, Lei; Showman, Adam P.

doi:10.1016/j.icarus.2010.11.034

Cited by 8 publications

(7 citation statements)

References 47 publications

(59 reference statements)

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“…In addition to basal heating, we assume that the ice layer is tidally heated. Tidal heating produces a heterogeneous heating pattern and its amplitude strongly depends on the orbit of the icy moons, their internal structure, and properties (e.g., Choblet et al, ;Kamata et al, ;Tobie et al, ) such that a detailed modeling of their evolution requires to couple orbital and thermal evolution (e.g., Běhounková et al, ; Han & Showman, , ; Hussmann & Spohn, ). Because of this coupling, the evolutions of icy moons depend not only on their own properties but also on the properties of the planet around which they orbit and its other satellites.…”

Section: Ice Layer As a Tidally Heated Convective Systemmentioning

confidence: 99%

Tidally Heated Convection and the Occurrence of Melting in Icy Satellites: Application to Europa

et al. 2020

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Observations of icy satellites have revealed widespread marks of cryovolcanism. Because aqueous cryomagmas are negatively buoyant, two processes are required to explain these observations: one mechanism to generate melt close enough to the surface and another one to transport this melt to the surface. Here, we investigate the generation of melting in a systematic way, using a set of 85 numerical simulations where we vary the viscosity contrast, Rayleigh number, and tidal heating rate. Applied to Europa, considering a hydrosphere composed of pure water, our simulations suggest that isolated melt pockets can be generated close to the surface ( ∼5 km) as long as the ice layer thickness ( d*) remains modest ( 15≤d*≤35 km). However, the generation of melting becomes increasingly difficult as the amount of antifreeze compounds in the subsurface ocean increases. Furthermore, the proportion of melting increases very sharply with increasing tidal heating rate. In particular, when the tidal heating rate exceeds a threshold, an asymptotic regime is reached where the surface heat flux remains constant indicating that the tidal heat generated above this threshold is only used for melting the ice shell. In that regime, we found a direct relationship between the surface heat flux and d*. Finally, we provide a new assessment of Europa's thermal state. Based on available constraints, we propose that the ice shell thickness should exceed 15 km. However, d*∼15–35 km implies a tidal power ( >2 TW) much larger than expected. An extrapolation of the trends suggested by our results indicates that a more reasonable tidal power ( ∼1 TW) would involve d*∼50–90 km.

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Section: Ice Layer As a Tidally Heated Convective Systemmentioning

confidence: 99%

Tidally Heated Convection and the Occurrence of Melting in Icy Satellites: Application to Europa

et al. 2020

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“…As for geophysical applications, the transient creep of polycrystalline ice is of interest e.g. for the behavior of ice shelves submitted to ocean tides [19,20] and for the heat production within icy satellites [21,22].…”

Section: Introductionmentioning

confidence: 99%

Experimental characterization of the intragranular strain field in columnar ice during transient creep

Grennerat¹,

Montagnat²,

Castelnau³

et al. 2012

Acta Materialia

112

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International audienceA digital image correlation (DIC) technique has been adapted to polycrystalline ice specimens in order to characterize the develop- ment of strain heterogeneities at an intragranular scale during transient creep deformation (compression tests). Specimens exhibit a columnar microstructure so that plastic deformation is essentially two-dimensional, with few in-depth gradients, and therefore surface DIC analyses are representative of the whole specimen volume. Local misorientations at the intragranular scale were also extracted from microstructure analyses carried out with an automatic texture analyzer before and after deformation. Highly localized strain patterns are evidenced by the DIC technique. Local equivalent strain can reach values as much as an order of magnitude larger than the macroscopic average. The structure of the strain pattern does not evolve with strain in the transient creep regime. Almost no correlation between the measured local strain and the Schmid factor of the slip plane of the underlying grain is observed, highlighting the importance of the mechanical interactions between neighboring grains resulting from the very large viscoplastic anisotropy of ice crystals. Finally, the experimental microstructure was introduced in a full-field fast Fourier transform polycrystal model; simulated strain fields are a good match with experimental ones

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“…Dislocation creep is then a priori the most appropriate deformation mechanism for subcritical convection. The reason why the piezometric grain size we predict is so high is detailed in section C. A large grain size may prevent the onset of convection in Enceladus's ice shell [ Barr and Pappalardo , ], even if tidal dissipation is considered [ Han and Showman , ; Běhounková et al , ]. However, we stress here that the proposed thermal regime for Enceladus consists more in a residual convection in the ice shell.…”

Section: Discussionmentioning

confidence: 98%

“…Besides, although some of our mobile lid, tidally heated simulations led to interestingly high heat fluxes in the SPT (see Figure ), tidal heating is probably overestimated in cases with a broad low‐viscosity region as we do not consider intrinsic latitudinal variations in our simple, first‐order approach (see section A). A fully consistent calculation of tidal dissipation will be one of the main next steps of our model, also taking into account the non‐Newtonian behavior in the tidal heating model [ Han and Showman , ]. The current heat production in Enceladus remains puzzling with regard to the most favorable value of 1.1 GW found for the equilibrium tidal dissipation [ Meyer and Wisdom , ] independently of Enceladus's internal structure or thermal state.…”

Section: Discussionmentioning

confidence: 99%

“…A detailed study on the onset of convection in a non-Newtonian fluid has been performed by Barr et al [2004]. Han and Showman [2011] also investigated the onset of convection with a consistent tidal heating model and a non-Newtonian rheology. The nonequilibrium dynamics of grain size is beyond the scope of the present study.…”

Section: Appendix C: Grain Size Stresses and Onset Of Convectionmentioning

confidence: 99%

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Self‐consistent generation of single‐plume state for Enceladus using non‐Newtonian rheology

et al. 2014

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The thermal dichotomy of Enceladus suggests an asymmetrical structure in its global heat transfer. So far, most of the models proposed that obtained such a distribution have prescribed an a priori asymmetry, i.e., some anomaly in or below the south polar ice shell. We present here the first set of numerical models of convection that yield a stable single-plume state for Enceladus without prescribed mechanical asymmetry. Using the convection code StagYY in a 2-D spherical annulus geometry, we show that a non-Newtonian ice rheology is sufficient to create a localized, single hot plume surrounded by a conductive ice mantle. We obtain a self-sustained state in which a region of small angular extent has a sufficiently low viscosity to allow subcritical to weak convection to occur due to the stress-dependent part of the rheological law. We find that the single-plume state is very unlikely to remain stable if the rheology is Newtonian, confirming what has been found by previous studies. In a second set of numerical simulations, we also investigate the first-order effect of tidal heating on the stability of the single-plume state. Tidal heating reinforces the stability of the single-plume state if it is generated in the plume itself. Lastly, we show that the likelihood of a stable single-plume state does not depend on the thickness of the ice shell.

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Coupled convection and tidal dissipation in Europa’s ice shell using non-Newtonian grain-size-sensitive (GSS) creep rheology

Cited by 8 publications

References 47 publications

Tidally Heated Convection and the Occurrence of Melting in Icy Satellites: Application to Europa

Tidally Heated Convection and the Occurrence of Melting in Icy Satellites: Application to Europa

Experimental characterization of the intragranular strain field in columnar ice during transient creep

Self‐consistent generation of single‐plume state for Enceladus using non‐Newtonian rheology

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