THE THIRD DATA POINT: FLUVIAL EROSION AND DRAINAGE NETWORK EVOLUTION ON TITAN

With the discovery of fluvial features on Saturn's moon Titan less than a decade ago, the number of worlds in the Solar system that are known to have experienced widespread, atmospherically driven fluvial activity grew from two (Earth and Mars) to three. This third data point comes with a twist: Titan's fluvial features have formed through runoff of liquid hydrocarbons over a crust composed primarily of water ice, offering a glimpse of familiar erosional processes operating under exotic conditions. A scarcity of impact craters indicates that geological processes have maintained a relatively young surface, but the extent to which fluvial processes have driven this resurfacing is unknown. Aside from a few tantalizing images of the Huygens probe landing site, our view of Titan's fluvial features is presently very coarse. Topographic measurements have revealed regional trends, but generally do not resolve even large fluvial landforms. Thus, at present, we face a challenge to reconstruct the evolution of Titan's landscape without the aid of fine-scale topography. We present our efforts to use landscape evolution models to relate map-view fluvial features visible in radar images to the cumulative amount of erosion that has occurred in different regions. We develop erosion proxies based on drainage basin shape and the sinuosity of elevation contours delineated by lake shorelines, and test these proxies on terrestrial landscapes where initial conditions and erosional histories can be constrained. Applying these proxies to Titan's surface suggests a picture of a young landscape that has been invaded by fluvial networks but has experienced relatively little spatially averaged erosion in some regions. We infer that fluvial networks are still expanding, even in more dissected areas such as the north polar region, and that Titan's young surface is a consequence of fluvial erosion in combination with other mechanisms.