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

Abstract

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.

Equation of State of SiC at Extreme Conditions: New Insight Into the Interior of Carbon‐Rich Exoplanets

“…We performed numerical simulations on a pure SiC mantle for a planet with one Earth mass (B3–B1 phase transition occurring around 1,830‐km depth), employing the thermodynamic parameters obtained in this study and the rheological data from Carter et al (). All details about the employed equations, numerical setup (Balay et al, ; Davis, ; Harlow & Welch, ; Hernlund & Tackley, ; Tackley, ), and boundary conditions (Rozel et al, ; Solomatov, ) are provided in Text S4. A surface thermal conductivity of 270 W·m −1 ·K −1 (Goldberg et al, ) was employed in this study.…”

Convection in Thin Shells of Icy Satellites: Effects of Latitudinal Surface Temperature Variations

“…Though the latitudinally variable T s case contains~10% more power than the homogenous case. This thermal configuration resembles the effectively low Rayleigh number non-Newtonian grain size-dependent computations of Rozel et al (2014), albeit focused along the equator due to the surface temperature gradient, as opposed to their pole-located plume. This indicates that an appropriately defined effective Rayleigh number may capture both cases, where Rozel et al's variations are due to locally higher mantle viscosity, and ours are due to temperature contrast variations.…”

Long‐term deformation driven by small ambient tectonic stresses and strong oscillating tidal within Enceladus with analogy to rock behavior near the San Andreas Fault

“…Convection is much more complicated, as local rate of tidal dissipation likely depends on the local temperature. Evolution of the object to a complicated thermal structure is a general expectation of a rheology where the strain rate nonlinearly on stress and temperature [ Rozel et al ., ].…”

“…Localization of Enceladus tectonics to one pole is reasonable and is a typical outcome for strongly nonlinear rheology [ Rozel et al ., ]. The envisioned process involves an instability where the depth of cracking suddenly jumps downward and buoyancy forces increase quickly.…”

“…Numerical models for convection within Enceladus recognize the importance of tidal heating and that near‐surface ice is likely weak near the South Pole [e.g., Barr and McKinnon , ; Barr , ; Barr and Preuss , ; O'Neill and Nimmo , ; Běhounková et al ., ; Han et al ., ; Besserer et al ., ; Showman et al ., ; Shoji et al ., ; Rozel et al ., ]. However, tides, frictional failure, and internal deformation appear to be coupled in multiple ways within Enceladus that have yet to be modeled numerically.…”