Canyon Formation on Charon and Tethys

The ocean worlds of the outer solar system are some of the foci for the search for water, and consequently the search for life. Studies suggest the presence of global subsurface water oceans on these bodies, either currently or in the past. Many of these worlds are moons of the large gas giants or dwarf planets. As a result, they have been subject to various forces related to their formation and their interactions with other moons as well as their parent planet. Tidal forces, changes in eccentricity, changes in rotation, internal processes, and impact cratering influence the surface features of these bodies. The surfaces of both Charon and Tethys, moons of Pluto and Saturn respectively, are marked by distinct linear features. Serenity Chasma on Charon and Ithaca Chasma on Tethys are large canyons that show characteristics suggesting they are rift zones, areas where the crust has thinned and stretched in response to stress. Linear features, both fractures and ridges, on Charon and Tethys have been interpreted as tensile features formed from the same types of stresses assumed to have formed the canyons. The current formation theories for these surface features, including the canyons, involve expansion from a frozen ocean. Water expands volumetrically as it freezes, thus the overlying icy crust would have to thin to accommodate the larger volumes of subsurface ice in the mantle. From this type of extensional stress, we expect to see rift zones in the crust, oriented isotropically (randomly and evenly). Instead, the canyons and tensile fractures on Charon and Tethys both show preferential directions of stress. Previously mapped features on Charon (Beyer et al., 2017; Robbins et al., 2019) will be compared against new results from Tethys. This study will map the orientation, distribution, and other characteristics of linear features on Tethys, in Cassini spacecraft images. By comparing the two sets of features, we seek to understand which factors may have contributed to the formation of the canyons on Charon and Tethys that resulted in such concentrations of stress. Tidal forces have been eliminated as a possible formation mechanism for tensile fractures on Charon (Rhoden et al., 2020). Thus, differences between the planets may be able to be attributed to the viability of formation mechanisms that have been eliminated for Charon, while similarities may suggest possible common forces on both planets.