Crater lakes on Titan: rings, horseshoes and bullseyes

Recent observations indicate that Titan has a predominantly icy surface, although photochemical models suggest that substantial amounts of liquid hydrocarbons may exist near or on the surface: the most plausible model of Titan's surface therefore is an icy one, with lakes or small seas of hydrocarbons (principally ethane), many in impact craters. Medium-sized craters will have central peaks, while large craters may undergo viscous relaxation, their centres doming upwards, to push the liquids into an annulus, thereby for-ming a ring lake. Additionally, craters with central pits may form ''bullseye'' lakes. The large tidal effects of Saturn on such lakes will affect their shape, distorting rings into horseshoes, and may also cause erosive migration.