PLUMBING A PLUME: USING STRUCTURAL GEOLOGY TO CONSTRAIN THE SUBSURFACE GEOMETRY OF THE ENCELADUS PLUME

Enceladus is a satellite of Saturn, inferred to have a global subsurface water ocean. The South Polar Terrain (SPT) “Tiger Stripes” eject jets of water vapor and icy grains are ejected into the space environment to form a plume many times the diameter of the satellite. Depending on how well-linked the plume and the ocean are, as modulated by the icy and liquid transport processes, the plume may provide an accessible environment to directly study a planetary ocean. While the plume of Enceladus likely sources to a global subsurface ocean, or deep reservoir fed by that ocean, we do not understand how water is transported from the subsurface liquid water reservoir to the surface. The goal of this work is to identify primary controls and potential configurations of a realistic plumbing system beneath Enceladus’ south polar jets. We will consider how subsurface fractures and permeable structures (e.g. porous regions) might manifest on Enceladus, ranging from individual, vertical, curtain-like fractures extending to the ocean beneath the four Tiger Stripes, to fractures with various dips and curvatures, to pre-existing networks of fractures throughout the ice shell volume, to permeable porous layers.

In order to constrain the subsurface plumbing on Enceladus, we must first create a new detailed structural map the surface fracture network, analyze the sensitivity to the changing tidal stress environment, and begin to project fracture networks into the subsurface. We will deploy advanced multiphysics models of varying complexity, using the WSP software FracMan, informed by the new mapping to evaluate how complex plumbing systems alter deformation and material transport at the surface, at depth, and through time. After initial modeling of the 2D and 3D structure, we will work on incorporating fluid and gas flow using the multiphysics flow model PFLOTRAN incorporated into FracMan. From this, we aim to determine distributions in the following key constraints with depth, time, and lateral location: permeability, active conduit aperture, active conduit orientation, mass of mobile material, fraction of material in each phase (solid, liquid, gas), material velocity for each phase, and residence timescale of each phase.