Geomorphology of Titan's Polar Regions

Abstract:

Numerous lakes and seas have been observed in Titan’s polar regions (Stofan et al., 2007), primarily at the north pole (Hayes et al., 2008), while evidence for channelized fluid flow has been found at all latitudes (Lorenz et al., 2008), though primarily at the poles as well. We construct a geomorphologic map of both poles at latitudes higher than 60⁰ using a combination of the Cassini Synthetic Aperture Radar images along with topographic data in the form of SARTopo (Stiles et al., 2009) and sparsely distributed Digital Terrain Models. Utilizing data from flybys Ta through T98, we define five governing morphologic units: plains, small depressions, large seas, mountains and ridge and valley networks. These units are subdivided according to their radar properties (bright or dark, uniformity), morphologies (degree of dissection, undulation, curvature and organization, regional slope), relative elevations and contact relations. These units are systematically mapped in a repeatable, quantitative manner along with various structural features such as remnant ridges, channels, alluvial fans and scarps. In combining SAR imagery with topographic data, our geomorphic map reveals a stratigraphic sequence from which we can infer processes. We find that the North Pole is dominated by an elevated, radar-dark plains unit, embedded by numerous filled, wet and dry small depressions with a sparse number of channels. The dark-plains unit transitions into a highly dissected radar-bright, lowland unit closer to the mare. A high density of radar-dark remnant ridges, channels and alluvial fans characterizes this unit. The South Pole is markedly different from the North, having far fewer lakes, no large filled seas, larger elevation gradients and a greater number of mountain regions while also being dominated by an organized ridge and valley network. Our work suggests the South Pole is not a drier version of the North. Rather the observed dichotomy between the two poles is likely the result of different governing surface process. While fluvial bedrock incision and overland flow processes may dominate the modern South Pole, the North appears to be primarily governed by dissolution and/or sublimation processes along with catastrophic overland flow events at the margins of the elevated, radar-dark plains.