Geological Conditions Required for the Fluvial Erosion of Titan’s Impact Craters
In comparison to other icy satellites, Titan has a small number of impact craters on its surface. Its dense atmosphere screens smaller impactors from the surface, but this alone does not account for the lack of impact craters, especially at large diameters. This suggests that Titan has a relatively young surface and/or erosional processes have effectively removed craters from its surface. For example, fluvial erosion could degrade craters such that they would be unrecognizable from an orbiting spacecraft such as Cassini. The amount of erosion, however, will depend on a number of factors including the geological and meteorological conditions of the region. A landscape evolution model coupled with different sets of geological parameters was used to simulate the fluvial erosion of relatively fresh impact craters on Titan. The focus was on varying the values of parameters such as bedrock and regolith erodibility, sediment grain size, the weathering rate of the regolith, and whether or not the regolith was saturated with liquid hydrocarbons. In some cases, it was found that only after changing the saturation state of the regolith mid-way through the model run was it possible to completely erode the crater. If the majority of fresh craters on Titan erode in a similar manner, the observed lack of impact craters on Titan could have implications for its climatic history. For example, one way to have a varying saturation state of the regolith is to have the atmospheric quantity of methane vary over time. This may occur due to episodic outgassing from methane clathrate within Titan’s crust. This process could allow for differences in the methane content of Titan’s atmosphere over geological time scales and in turn, the amount of surface liquids and erosion.