Numerical modeling of impact cratering on Titan with implications for the age of Titan''s surface

Introduction. Results reported from the first two close flybys of Titan reveal few if any impact craters exposed at the surface[1], suggesting that geological or atmospheric processes, or both, have worked to prevent the formation of craters or to hide or erase them after formation. Here we quantify some of these processes and use them to constrain the age of Titan’s surface: atmospheric and oceanic shielding, flooding by the ocean beneath a thin crust, viscous relaxation, and burial by sedimenting atmospheric aerosols. Numerical methods and initial conditions. We use the Eulerian two-dimensional hydrocode SALE [2,3]. The code is complemented by the Tillotson equation of state for water and ice [4] and by ice strength properties from published laboratory data [5]. Weak icy bodies (hereafter, “comets”), strike Titan vertically in the simulations with an average impact velocity on Titan of 11 km/s [6]. We use a detailed engineering model for the atmosphere stratification on Titan [7]. The surface temperature is assumed constant at 93 K. To model large impacts we include a waterammonia ocean (dehydrate composition) beneath the crust with a temperature of 176 K. According to models [8] the thickness of the ice crust on Titan varies from 125 km (5% of ammonia) to 67 km (15% of ammonia). A recent study of Titan’s orbit evolution [9] favors the higher content of ammonia, hence a thin crust and deep mantle ocean..