How Enceladus' Geysers are Tied to its Geological Features

ENCELADUS' GEYSERS: RELATION TO GEOLOGICAL FEATURES

Authors:

Helfenstein et al

Abstract:


We apply histogram analysis, photogeological methods, and tidal stress modeling to Porco et al.'s survey of 101 Enceladus South Polar Basin geysers and their three-dimensional orientations to test if the jet azimuths are influenced by their placement relative to surface morphology and tectonic structures. Geysers emplaced along the three most active tiger stripe fractures (Damascus Sulcus, Baghdad Sulcus, and Cairo Sulcus) occur in local groupings with relatively uniform nearest-neighbor separation distances (~5 km). Their placement may be controlled by uniformly spaced en echelon Riedel-type shear cracks originating from left-lateral strike-slip fault motion inferred to occur along tiger stripes. The spacing would imply a lithosphere thickness of ~5 km in the vicinity of the tiger stripes. The orientations of tilted geyser jets are not randomly distributed; rather their azimuths correlate with the directions either of tiger stripes, cross-cutting fractures, or else fine-scale local tectonic fabrics. Diurnal tidal stress modeling suggests that periodic changes of plume activity are significantly affected by cross-cutting fractures that open and close at different times than the tiger stripes that they intersect. We find evidence of sub-kilometer scale morphological modification of surface geological features surrounding geysers from sublimation-aided erosion, and ablation, and scouring. We propose that the simultaneous crushing and shearing action of periodic transpressional tidal stress on ice condensing on the inside walls of geyser conduits is the mechanism that extrudes the peculiar, paired narrow ridges known as "shark fins" that flank the medial tiger stripe fissures. We present a gallery of high-resolution image mosaics showing the placement of all the jets in their source region and consequently their geological context.