Topographic Relaxation of Complex Impact Craters in a Clathrate Crust on Titan

Abstract Titan’s impact craters are significantly shallower than fresh craters on Ganymede, which are often used as templates for fresh craters on Titan. The presence of a clathrate crust on Titan, which would insulate the ice shell and maintain warmer ice near the surface, may contribute to the shallowness of its craters. Research into the effects of a clathrate crust on the topographic relaxation of craters found that a 5–10 km thick clathrate crust may explain their shallowness. That previous study simulated simple, bowl-shaped craters with Ganymede-derived depths. However, if craters are initially like Ganymede’s, they will exhibit complex rather than simple morphologies. Therefore, we model the relaxation of more realistic shapes incorporating short-wavelength features (central peaks, pits, and pit-rims), floor widths, and rimwall slopes derived from Ganymede’s fresh complex craters. We simulate topographic relaxation of craters 40–100 km in diameter in ice shells with 5–20 km thick clathrate crusts. We find that most crater depths can be reproduced in 5–15 km thick clathrate crusts. Notably, simulated short-wavelength central features remain or grow during relaxation. Evidence of central features is rare, suggesting that additional processes modify Titan’s craters. To fill the remaining flexural moats, 300–1000 m of infill is required, while 200–400 m may need to erode from elevated central features to flatten the relief. We conclude that topographic relaxation may be partially responsible for the shallowness and that erosion and infill are responsible for the dearth of central features in Titan’s craters.