The case for water ice in Titan’s near subsurface

Abstract : Titan’s deep crust is thought to be made of water ice in its solid form or as clathrate hydrates. However, its actual expression on the surface has proven ambiguous. Only regions possibly enriched in water ice have been identified by the Visible and Infrared Mapping Spectrometer (VIMS) on board Cassini. Overall, the surface of Titan seems to be covered by a sedimentary layer of solid organics, likely originating from methane photolysis in the atmosphere. Nevertheless, the thickness of this layer may vary across Titan and the best chance for detecting water ice is in the microwave region where greater depths into the surface are probed. Considering both the active and passive data collected by the RADAR on board Cassini, we will show that the presence of water ice in the near subsurface is strongly indicated by the high degree of volume scattering observed in radar-bright/low-emissive regions (mountain-like terrains) comprising ~ 10% of Titan’s surface. The rims of several craters also demonstrate unique characteristics in the microwave that suggest the presence of water ice. The impacts that caused these features can be expected to expose material from the deep subsurface, certainly bringing large quantities of ice to the surface. We will discuss the implications of these findings.