The impact of a pressurized regional sea or global ocean on stresses on Enceladus

摘要

Liquid water is likely present in the interior of Enceladus, but it is still debated whether this water forms a global ocean or a regional sea and whether the present-day situation is stable. As the heat flux of Enceladus exceeds most heat source estimates, the liquid water is likely cooling and crystallizing, which results in expansion and pressurization of the sea or ocean. We determine, using an axisymmetric Finite Element Model, the tectonic patterns that pressurization of a regional sea or global ocean might produce at the surface of Enceladus. Tension is always predicted above where the ice is thinnest and generates cracks that might be at the origin of the Tiger Stripes. Tectonic activity is also expected in an annulus around the sea if the ice shell is in contact with but slips freely along the rocky core of the satellite. Cracks at the north pole are expected if the shell slips along the core or if there is a global ocean with thin ice at the pole. Water is likely injected along the base of the ice when the shell is grounded, which may lead to cycles of tectonic activity with the shell alternating between floating and grounded states and midlatitude faulting occurring at the transition from a grounded to a floating state. Plain Language Summary Saturn's Icy Moon, Enceladus, is likely to have an internal sea or ocean, which may be cooling and freezing to solid ice. As this happens, ice expands and increases the pressure in the interior ocean, stressing and fracturing the surface of the satellite. We find evidence in the pattern of deformation observed at the surface of Enceladus that the ice shell used to be in contact with its rocky core. If the ocean is global, regions of thin ice at both the south pole and north pole are needed to explain fractures there. The ice shell of Enceladus may alternate between states where it is in contact with the core or floating over the ocean in a sort of global freeze-thaw cycle.