Thermo‐compositional convection in Europa's icy shell with salinity

Han, Lei; Showman, Adam P.

doi:10.1029/2005gl023979

Cited by 49 publications

(49 citation statements)

References 28 publications

(45 reference statements)

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“…This might then promote a true polar wander of Enceladus, leading to a natural, poleward reorientation of the structure [ Nimmo and Pappalardo , ]. However, purely thermal density contrasts, as those obtained here, are much less favorable to reorientation than chemical ones [ Nimmo and Pappalardo , ]; the latter may develop through thermochemical convection in Enceladus's ice shell, though [ Han and Showman , ; Stegman et al , ]. A potentially more realistic “reorientation" mechanism would be a simple (slow) migration of the low viscosity region toward the south pole, where tidal heating would be optimally efficient.…”

Section: Discussionsupporting

confidence: 88%

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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Section: Discussionsupporting

confidence: 88%

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

et al. 2014

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“…The present study is based on the simplification that our modeled synthetic gravity signal has contributions only from the gravity anomalies originating from the ice layer and the silicate crust at the ocean floor, with other contributions neglected. Other possible contributions of the outer ice and water layer to the signal could be warm ice convection [e.g., Hussmann et al , 2002; Tobie et al , 2003; Han and Showman , 2005], density anomalies in the ice shell [cf. Nimmo and Manga , 2009] and hydrothermal plumes in the subsurface ocean [e.g., Thomson and Delaney , 2001; Goodman et al , 2004; Vance and Brown , 2005].…”

Section: Summary and Discussionmentioning

confidence: 99%

Gravity signals on Europa from silicate shell density variations

2010

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[1] Future missions to Jupiter's moon Europa will attempt to measure the gravity field of this planetary body. Here, we study the detectability of silicate shell density variations in the gravity field. The first step in the gravity processing will be to remove the gravity signal of the ice shell. The detection of the ice shell signal, however, can be technologically challenging depending on its thickness and compensation state since the predicted anomalies are only a few mGals or even smaller. For long-wavelength topography below degree 40, the signal of the silicate shell will likely dominate the gravity field. Assuming that the anomalies of the silicate shell are only caused by the ocean floor topography, thus neglecting possible density anomalies in the mantle, we should be able to detect the ocean floor signal even if its topographic variations are only a few hundred meters. When studying the gravity signal of isolated midsize topographic features like volcanoes, we find a good chance of detecting objects with a size of 75-200 km with measurement accuracy of 1 mGal. Owing to the large number of unknown parameters for the gravity inversion, the reconstruction of a global ice-water/silicate interface shape is uncertain, in particular, as possible contributions to the gravity field from a low-degree convecting mantle cannot be distinguished. The comparison between the standard measurement technique of Doppler tracking (detecting the gravity anomalies) and a microgradiometer (measuring gravity gradients) shows that the latter will not improve the detectability of the ocean floor structures.

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“…Furthermore, detailed numerical calculations revealed that it is difficult to reproduce the observed morphology through a thermal diapir mechanism [ Showman and Han , , ]. In addition to thermal buoyancy, compositional buoyancy can generate a diapir [ Pappalardo and Barr , ; Han and Showman , ]; a compositional density difference actually generates a larger buoyancy than thermal diapirism. In addition to Europa, compositional diapirism has been suggested as the origin of the cell‐like morphology of Triton [ Schenk and Jackson , ].…”

Section: Introductionmentioning

confidence: 99%

Compositional diapirism as the origin of the low‐albedo terrain and vaporization at midlatitude on Ceres

Dake

Kurita

2014

JGR Planets

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Recent observations of Ceres, made using the Heterodyne Instrument for the Far Infrared on board the European Space Agency's Herschel Space Observatory, have shown that water vapor is emanated from the low‐albedo midlatitude regions. Based on the supposition that some dark spots on Europa may be caused by diapirism, we explored whether Ceres' environment also can induce compositional diapirism, and whether an upwelling diapir could explain the origin and distribution of the dark spots and vaporization of Ceres. If the density of the rock that constitutes Ceres is around 2700 kg m−3, the undifferentiated crust is stable over geological time periods at less than 180 K. At a surface temperature of 170 K, a diapir can reach the surface if the crust is a few tens of kilometers thick. Alternatively, if the surface temperature is 150 K, a large contrast in viscosity would prevent diapirs from reaching the surface. The relatively moderate surface temperature in the midlatitude regions of Ceres may be the reason for the formation of dark terrains occurring only in such areas. Our finite difference calculations do not show that diapirism melts the surface ice because the temperature gradient changes very little. However, if the observed vapor emission is caused by the sublimation of fresh ice, compositional diapirism could be the mechanism that transports the fresh ice to the surface. In addition to other mechanisms such as cryovolcanism, diapirism is a valid hypothesis for explaining the dark terrain and vapor emissions of Ceres.

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Thermo‐compositional convection in Europa's icy shell with salinity

Cited by 49 publications

References 28 publications

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

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

Gravity signals on Europa from silicate shell density variations

Compositional diapirism as the origin of the low‐albedo terrain and vaporization at midlatitude on Ceres

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