Enceladus: Present internal structure and differentiation by early and long-term radiogenic heating

Schubert, G.; Anderson, J. D.; Travis, B. J.; Palguta, J.

doi:10.1016/j.icarus.2006.12.012

Cited by 151 publications

(149 citation statements)

References 32 publications

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“…The mechanism of the source of heat remains controversial, with tidal deformation and radioactive decay as major contenders (10,30,31). (Both these mechanisms are compatible with our model of Enceladus.)…”

supporting

confidence: 78%

Unified model of tectonics and heat transport in a frigid Enceladus

Gioia¹,

Chakraborty

Marshak

et al. 2007

Proc. Natl. Acad. Sci. U.S.A.

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Recent data from the Cassini spacecraft have revealed that Enceladus, the 500-km-diameter moon of Saturn, has a southern hemisphere with a distinct arrangement of tectonic features, intense heat flux, and geyser-like plumes. How did the tectonic features form? How is the heat transported from depth? To address these questions, we formulate a simple model that couples the mechanics and thermodynamics of Enceladus and gives a unified explanation of the salient tectonic features, the plumes, and the transport of heat from a source at a depth of tens of kilometers to the surface. Our findings imply that tiny, icy moons can develop complex surficial geomorphologies, high heat fluxes, and geyserlike activity even if they do not have hot, liquid, and/or convecting interiors. E nceladus, the 500-km-diameter moon of Saturn, is the smallest body in the solar system with erupting plumes (1). On the southern hemisphere, Enceladus displays tectonic features that are closely related to the plumes, a thermal anomaly that straddles the south pole, and high rates of heat flow in coincidence with the thermal anomaly (2, 3). The tectonic features include four 130-km-long fractures that cut across the thermal anomaly and are known as ''tiger stripes'' (2, §). The plumes observed by Cassini gushed from vents located on the tiger stripes (5); these plumes had a total discharge similar to the Old Faithful geyser in Yellowstone National Park and consisted of H 2 O, CH 4 , N 2 , and CO 2 gases laden with ice crystals (1, 2, 6).The cause of plume eruption has been addressed by two antithetic models so far. In one model, called ''Cold Faithful,'' Enceladus has a shell of H 2 O ice with pockets of liquid water at depths as shallow as 7 m (2). Cold Faithful's plumes erupt where small fractures decompress the pockets of liquid water, causing the liquid water to boil at a temperature of at least 273 K. The small fractures may form (and the attendant plumes erupt) at any time, driven by tectonic disturbances. Thus, the plumes of Cold Faithful may remain active over long periods of time.In the other model, called ''Frigid Faithful,'' Enceladus has a shell of H 2 O ice and H 2 O clathrates (CO 2 , CH 4 , N 2 ) topped with a layer of H 2 O-CO 2 ice (Fig. 1) (7). Frigid Faithful is based on the assumption that the composition of the plumes observed by Cassini indicates the composition of the shell where the plumes originate. The plumes of Frigid Faithful erupt where large fractures (the tiger stripes) expose and decompress some clathrates of the clathrate-rich shell, causing these clathrates to absorb heat from a source at depth and then to dissociate at a temperature that might be as low as Ϸ133 K, the average temperature of the hotspots that have been observed on the surface of the south pole (3). The tiger stripes need to form and expose some clathrates of the shell only once, possibly long ago in geologic time. Although clathrate dissociation is, in principle, self-limiting (because the products of dissociation may refreeze), it is also explos...

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supporting

confidence: 78%

Unified model of tectonics and heat transport in a frigid Enceladus

Gioia¹,

Chakraborty

Marshak

et al. 2007

Proc. Natl. Acad. Sci. U.S.A.

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“…It is likely that liquid water did not simply fill the porosity of the parent bodies but circulated in a convective manner similar to what is observed in geothermal systems in Earth's crust [2]. Hydrothermal convection through rocky spherical shells is also likely to have occurred or to be presently active in a number of outer planet icy satellites that have water-ice shells surrounding rocky cores, among which are Europa and Enceladus [3]. Understanding the flow structure of hydrothermal convection in a sphericalshell porous medium helps us elucidate the evolution of these celestial bodies.…”

mentioning

confidence: 93%

Hydrothermal Convection in Moderately Thin Spherical Shells

et al. 2008

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Hydrothermal convection of pore water with a temperature-dependent viscosity within a permeable, internally heated, moderately thin spherical shell is investigated by both a perturbation analysis and a direct numerical simulation. The analysis and simulation are mainly focused on a thin spherical shell in that convective instabilities are characterized by the spherical harmonic degree l 6 with a 13-fold mathematical degeneracy. Four different three-dimensional analytical solutions of convection are derived by removing the degeneracy through the nonlinear effect. A direct numerical simulation of the nonlinear problem is also carried out, showing satisfactory agreement between the analytical solutions and the numerical simulations.

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“…Some species, like for instance CO 2 , might be primordial, whereas others, like N 2 , might require a liquid water reservoir in the interior at elevated temperatures, enabling aqueous, catalytic chemical reactions [23]. Taken together, the evidence strongly suggests that Enceladus' interior is at least partially differentiated into a silicate-metal core overlain by a water ice-liquid water shell [37]. However, the energy source required to initiate and preserve activity at the level comparable to that observed today over geologic periods and the concentration of geologic and thermal activity towards the south-polar region are still not well understood.…”

Section: Origin Of Titan and Enceladusmentioning

confidence: 96%

TandEM: Titan and Enceladus mission

et al. 2008

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International audienceTandEM was proposed as an L-class (large) mission in response to ESA's Cosmic Vision 2015-2025 Call, and accepted for further studies, with the goal of exploring Titan and Enceladus. The mission concept is to perform in situ investigations of two worlds tied together by location and properties, whose remarkable natures have been partly revealed by the ongoing Cassini-Huygens mission. These bodies still hold mysteries requiring a complete exploration using a variety of vehicles and instruments. TandEM is an ambitious mission because its targets are two of the most exciting and challenging bodies in the Solar System. It is designed to build on but exceed the scientific and technological accomplishments of the Cassini-Huygens mission, exploring Titan and Enceladus in ways that are not currently possible (full close-up and in situ coverage over long periods of time). In the current mission architecture, TandEM proposes to deliver two medium-sized spacecraft to the Saturnian system. One spacecraft would be an orbiter with a large host of instruments which would perform several Enceladus flybys and deliver penetrators to its surface before going into a dedicated orbit around Titan alone, while the other spacecraft would carry the Titan in situ investigation components, i.e. a hot-air balloon (Montgolfière) and possibly several landing probes to be delivered through the atmospher

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Enceladus: Present internal structure and differentiation by early and long-term radiogenic heating

Cited by 151 publications

References 32 publications

Unified model of tectonics and heat transport in a frigid Enceladus

Unified model of tectonics and heat transport in a frigid Enceladus

Hydrothermal Convection in Moderately Thin Spherical Shells

TandEM: Titan and Enceladus mission

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