Surface Processes on the Mid-Sized Moons of Saturn
Abstract
Saturn’s mid-sized icy moons display a range of surface processes. In this dissertation, we used spacecraft data to explore the surfaces of two moons, Tethys and Enceladus. Both moons are small, inner moons made largely of water ice. However, Tethys is inactive, with only a record of past tectonic activity, while Enceladus has a water-ice plume. First, we examined the small linear surface features on Tethys. Tethys is not expected to be geologically active, but its surface shows evidence of tectonic features. To better understand the moon’s history, we used images from the Cassini mission and mapped six types of features (including pit chains, tectonic fractures, impact-related crater chains, and ridges) and analyzed their locations, orientations, and origins. The maps from this work can be used for future hypothesis testing, to understand which processes and tectonic forces influenced Tethys’s surface evolution. We then used change detection to study Tethys and to compare it against Enceladus. For both moons, we examined pairs of optical images taken between 2004 and 2017 during the Cassini mission. We overlaid images from different years to look for surficial changes. On Enceladus, we found two changing albedo features and one image pair with unusual lighting that may have produced a candidate change. On Tethys, we observed no obvious changes. One of the candidate changes on Enceladus, the Black Spot, resembles a recent impact crater. This places limits on the impact cratering flux in the Saturnian system. We concluded that the Black Spot is a true albedo feature fading with time as it is covered up by plume deposits. Comparing to the literature, we suggest that deposition rates may be higher than the lower limits previously placed. Overall, we have expanded our understanding of the historic and present surface processes on Tethys and Enceladus, placing limits on tectonic processes, impact cratering, and surface deposition there. These results help us to better understand other icy moons and create a foundation that can be expanded on as we continue to explore the outer solar system.