THE IMPORTANCE OF STRESSES FROM A PRESSURIZED REGIONAL SEA ON ENCELADUS (Invited Presentation)

Enceladus is a geologically active icy satellite of Saturn with a radius of only 252 km. The south polar terrain (SPT) is a heavily fractured, geologically young region that contains the source of the active jets erupting from the largest fissures in the region. An analysis of the fractures at the SPT may provide insight into the sources of stress on Enceladus both now and in the past. The most commonly considered sources of stress are related to tidal activity and ice shell thickening. Models that consider tidal stresses provide valuable insight but commonly assume a uniform ice shell thickness, which may not be the case if there is a regional sea or deeper ocean beneath the SPT.

By comparing the orientation and concentration of stresses resulting from a pressurized ocean we can gain insight into the possible internal structure of Enceladus. Using the Anderson faulting criteria allows for a prediction of the style of near surface faulting.

Using an axisymmetric model developed using COMSOL Multiphysics™ several possible geometries of the internal structure of Enceladus are modeled: including a range of subsurface sea sizes (lateral extent and thickness), ice shell thicknesses, and both an ice shell bonded to the rocky interior as well as an ice shell riding on a frictionless surface. The basal boundary conditions have important implications for the ice shell stresses and therefore the type of faulting predicted. A decoupled ice shell transmits stresses to the northern hemisphere. A thinner cryosphere is more likely to result in near surface yielding at the South Pole. Similarly, a thick regional sea also results in an increase in stresses at the South Pole.

Several yielding regimes are predicted based on model geometry. The classification of the surface yielding predicted by the range of model geometries considered is used to constrain model geometries for further consideration. Analysis of the stresses at the base of the ice shell suggests that a pressurized sea would result in at least a partial decoupling of the ice shell from the rocky interior. Model results suggest that there may be a narrow range of ocean geometries that are consistent with observations of the yielding at the South Pole.