Unified model of tectonics and heat transport in a frigid Enceladus

Abstract

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 geyser-like activity even if they do not have hot, liquid, and/or convecting interiors.

Fig. 1.

Schematic of Frigid Faithful. In the text, we argue that the tiger stripes (and the advection of heat by the fast-moving, gaseous products of clathrate dissociation) extend to a depth of ≈35 km, turning the shell of Enceladus into a deep and frigid “advection machine.” The plumes are but leaks in this advection machine.

Fig. 2.

Map of the major tectonic features on the southern hemisphere of Enceladus. [Based on figure 2 in Porco et al. (2) and The Enceladus Atlas (19).] The region shown in green is the annular region that surrounds the TST and contains modest topography.

Fig. 3.

Mechanical model explaining the formation of the tectonic features on the southern hemisphere. (A) Plan view and cross-section view of the mechanical model with a square TST. The pole is marked SP. (B) Stress element with stresses σ_x and σ_y. (C) Surface stresses along the x or y axis for the mechanical model with a square TST. (D) Tectonic features associated with the mechanical model with a square TST.

Fig. 4.

Mechanical model explaining the formation of the tectonic features on the southern hemisphere, including the orientation of the tiger stripes. (A) Plan views of the mechanical model with a square TST and the mechanical model with a rectangular TST. The pole is marked SP. (B) Surface stresses along the x axis for the mechanical model with a rectangular TST. (C) Surface stresses along the y axis for the mechanical model with a rectangular TST. (D) Tectonic features associated with the mechanical model with a rectangular TST. (Inset) Cross-sectional slice of cracked material of thickness w.