Antarctic Analog for Diurnal Tidal Motions along Fractures on Enceladus

Recent CASSINI VIMS observations have revealed a diurnal variation in the brightness of plume observations from Enceladus. The plume brightness varies by a factor of four as Enceladus orbits Saturn. The plume brightens dramatically as Enceladus approaches its orbital apocenter, and is dimmer near pericenter. The brightness is linked to the amount of material being erupted from the Tiger Stripe fractures in Enceladus' south polar region. The observation of variations in plume brightness (or eruptive output) supports a theoretical model of diurnal tidal stress controlling the location and timing of eruptions from these fractures. Diurnal tidal stress will cyclically place these fractures under tension and compression, which may cause the Tiger Stripes to open and close daily. If conduits to subsurface volatile reservoirs were established while fractures are in tension, the tidally-controlled fault motion would dictate the eruptive output. . This tidal stress model predicts that the Tiger Stripes would experience more tensile stresses near apocenter, thus facilitating more eruptive activity at that time. Tidal stress calculations are based on the tidal flexing expected to occur on Enceladus; surface deformation in response to tidal stresses can only be inferred. The predicted fault motions are small and are not currently observable. However, an Earth analog from the Ross Ice Shelf, Antarctica, may provide insight for the process of induced diurnal tidal motions. Rifts on Antarctic ice shelves are tensile fractures in the floating ice shelf. While the rifts on the Ross Ice Shelf exhibit secular dilation, which causes them to widen with time, data of their motion also show a distinctly diurnal signal. The Ross Ice Shelf experiences tidal forces from both the Moon and Sun, and these forces induce small tidal motions on rifts in the ice shelf. GPS data show small, diurnal tidal motions that dilate and constrict the rift daily. From this analog we conclude that the diurnal tidal motion model for Enceladus may be credible.