Topographic Stress as a Mechanical Weathering Mechanism on Titan

Titan is unique among icy moons for its active surface processes and extensive erosional features. The presence of coarse sediment suggests that mechanical weathering breaks down Titan's surface material, but the exact processes of mechanical weathering are unknown. We tested the idea that topographic features perturb ambient crustal stresses enough to generate or enhance fractures. We used a two-dimensional boundary element model to predict the likely stress state within hypothetical erosional landforms on Titan, including river valleys and isolated ridges, and to model the locations and types of resulting fractures. Our results suggest that topographic stress perturbations are indeed sufficient to generate fractures and drive mechanical weathering, with little sensitivity to the density of the material making up Titan's crust and landforms and no dependence on its elastic moduli. For material density of 800 to1,200 kg/m³, opening-mode failure is predicted to occur within hypothetical Titan landforms with a width of hundreds of meters, relief of tens of meters or more, and horizontal tidal or tectonic stresses up to 1 MPa of compression, which encompasses typical predicted tidal stresses ranging between 10 kPa of compression and 10 kPa of tension. Under the same conditions, shear fracture is predicted to occur if the cohesion of the material is less than 100 kPa or if pore fluid pressures reduce local effective normal stresses. We therefore suggest that Titan's crust may be highly fractured and permeable, and that the predicted fractures could help generate sediment and provide pathways for subsurface transport of fluids.