Constraining the Lifespan of the South Polar Plume on Enceladus using Tectonic Pit Chains

On Enceladus, pit chains are observed primarily within the cratered terrains on the Saturnian and Anti-saturnian hemispheres. Tectonically formed pit chains have been used to signal the presence of loose, unconsolidated material we refer to as regolith. Regolith deposited on Enceladus may have originated from three different sources: 1) impact craters, 2) plume fall-back, 3) deposition of E ring material. Regolith thicknesses are likely to vary spatially across Enceladus due to variations in jet localities, eruption directionality, and preservation of like impact crater-generated regolith.

We have adapted a technique for inferring the volume of individual pits into a tool for inferring the minimum depth of the regolith in which that pit forms. Using the pit diameter, length of shadow inside the pit and the sun angle, we can infer the depth of an individual pit. The pit depth is therefore the assumed depth of the regolith it forms in: this is a minimum estimate because we cannot know whether the pit extends to the base of the regolith.

We present an updated global map of the distribution of pit chains across the surface of Enceladus, as well a map of where we have measured the depth of the regolith from individual pits. We find that regolith depths across the surface of Enceladus range from 80 meters to ~1 km. The median regolith depth is approximately 400 m which could take as little as 400,000 years or as many as 4 Ga to deposit, depending on the modeled deposition rate at a given location.

We present updated and refined estimates of regolith depths including estimates that consider the contribution of impact generated regolith. We also present refined estimates of the time needed for the deposition plume-generated regolith, which will constrain a lower-limit on the age of plume activity.