Effect of Methane Clathrate on Crater Size and Implications for the Age of Titan's Surface

Saturn’s largest satellite, Titan, is sparsely cratered, suggesting its surface is relatively young and is being actively eroded or resurfaced. Details on the age of this surface have implications for the duration and efficiency of such erosional and resurfacing processes from Titans’ thick atmosphere. Current estimates put the age of Titan’s surface at ~200 Myr to 1 Gyr, based on the observed size-distribution of Titan’s craters. These past studies, however, have not considered the role that liquid methane plays in the formation of craters on Titan. Methane may interact with Titan’s icy crust, creating a layer of methane clathrates. Methane clathrates can influence the cratering process in several ways. Methane clathrate is stronger than water-ice, which can reduce crater diameters. Clathrates, however, also have lower thermal conductivity, which will lead to higher temperature profiles, bringing warmer water ice closer to the surface. As a result, craters formed into a surface covered with a methane clathrate layer will have significantly different diameters and depths than those formed in the pure water ice target. Thus, the previous determination of the impactor population responsible for the observed size-distribution of Titan’s crater may be in error. In this work we will conduct a series of impact simulations into targets comprising layers of methane-clathrate and water ice to derive a more accurate age of Titan’s surface.

We will consider a range of clathrate layer thicknesses (from which thermal profiles are predicted) to derive improved relations between crater size and impactor diameter. We will then use these relations to convert the observed size-distribution of Titan’s craters into impactor size-frequency distributions, repeating this for each of the clathrate layer thicknesses we consider. Next we will use previously published atmospheric ablation models to correct these impactor size-frequency distributions. Finally, we will use these results with published size-dependent impact fluxes at Saturn to derive corrected estimates of the age of Titan’s surface.