The fluffy core of Enceladus

Roberts, J. H.

doi:10.1016/j.icarus.2015.05.033

Cited by 78 publications

(97 citation statements)

References 43 publications

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“…The first option suggests that tidal heating was even more powerful in a recent past, probably due to higher eccentricity [e.g., Běhounková et al, 2012], allowing the formation of a very thin ice shell which is now growing. The second option implies a very efficient dissipation process in the interior, possibly in an unconsolidated core as proposed by Roberts [2015] or in the ocean [e.g., Tyler, 2011]. However, it is still unclear whether dissipation in a water-saturated porous core and heat transport through the ocean could explain the present-day structure.…”

Section: Implications For Geological and Thermal History Of Enceladusmentioning

confidence: 99%

Enceladus's internal ocean and ice shell constrained from Cassini gravity, shape, and libration data

Čadek

Tobie

Hoolst

et al. 2016

Geophysical Research Letters

159

141

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The intense plume activity at the South Pole of Enceladus together with the recent detection of libration hints at an internal water ocean underneath the outer ice shell. However, the interpretation of gravity, shape, and libration data leads to contradicting results regarding the depth of ocean/ice interface and the total volume of the ocean. Here we develop an interior structure model consisting of a rocky core, an internal ocean, and an ice shell, which satisfies simultaneously the gravity, shape, and libration data. We show that the data can be reconciled by considering isostatic compensation including the effect of a few hundred meter thick elastic lithosphere. Our model predicts that the core radius is 180–185 km, the ocean density is at least 1030 kg/m3, and the ice shell is 18–22 km thick on average. The ice thicknesses are reduced at poles decreasing to less than 5 km in the south polar region.

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Section: Implications For Geological and Thermal History Of Enceladusmentioning

confidence: 99%

Enceladus's internal ocean and ice shell constrained from Cassini gravity, shape, and libration data

Čadek

Tobie

Hoolst

et al. 2016

Geophysical Research Letters

159

141

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“…In addition, radiogenic heating is assumed to be the only heat source in the core, though tides may also be important (e.g., Choblet et al, 2017;Roberts, 2015). The rheology of pure water ice is assumed; inclusions of other molecules would change the viscosity of the ice shell (Durham et al, 2010) and may affect the thermal evolution of satellites.…”

Section: 1002/2017je005404mentioning

confidence: 99%

One‐Dimensional Convective Thermal Evolution Calculation Using a Modified Mixing Length Theory: Application to Saturnian Icy Satellites

Kamata

2018

JGR Planets

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Solid‐state thermal convection plays a major role in the thermal evolution of solid planetary bodies. Solving the equation system for thermal evolution considering convection requires 2‐D or 3‐D modeling, resulting in large calculation costs. A 1‐D calculation scheme based on mixing length theory (MLT) requires a much lower calculation cost and is suitable for parameter studies. A major concern for the MLT scheme is its accuracy due to a lack of detailed comparisons with higher dimensional schemes. In this study, I quantify its accuracy via comparisons of thermal profiles obtained by 1‐D MLT and 3‐D numerical schemes. To improve the accuracy, I propose a new definition of the mixing length (l), which is a parameter controlling the efficiency of heat transportation due to convection, for a bottom‐heated convective layer. Adopting this new definition of l, I investigate the thermal evolution of Saturnian icy satellites, Dione and Enceladus, under a wide variety of parameter conditions. Calculation results indicate that each satellite requires several tens of GW of heat to possess a thick global subsurface ocean suggested from geophysical analyses. Dynamical tides may be able to account for such an amount of heat, though the reference viscosity of Dione's ice and the ammonia content of Dione's ocean need to be very high. Otherwise, a thick global ocean in Dione cannot be maintained, implying that its shell is not in a minimum stress state.

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“…Tidal dissipation is the most likely source of power for the observed geological activity (Nimmo et al, ). Current models, however, have so far been unable to account for the observed ∼10 GW of endogenic heat flow emanating from the south polar region (Howett et al, ; Spencer et al, ) without invoking the presence of a highly porous (“fluffy”) solid inner core (Choblet et al, ; Roberts, ) or a convecting icy crust (Běhounková et al, , ). As suggested by Barr and McKinnon (), this latter hypothesis appears unlikely in view of the relatively small thickness of the crust (∼20 km) deduced from geodetic observations (Beuthe et al, ; Čadek et al, ).…”

Section: Introductionmentioning

confidence: 99%

Internal Energy Dissipation in Enceladus's Subsurface Ocean From Tides and Libration and the Role of Inertial Waves

et al. 2019

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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.

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The fluffy core of Enceladus

Cited by 78 publications

References 43 publications

Enceladus's internal ocean and ice shell constrained from Cassini gravity, shape, and libration data

Enceladus's internal ocean and ice shell constrained from Cassini gravity, shape, and libration data

One‐Dimensional Convective Thermal Evolution Calculation Using a Modified Mixing Length Theory: Application to Saturnian Icy Satellites

Internal Energy Dissipation in Enceladus's Subsurface Ocean From Tides and Libration and the Role of Inertial Waves

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