CRATER LAKES ON TITAN - RINGS, HORSESHOES AND BULLSEYES

Recent observations indicate that Titan has a predominantly icy surfac e, although photochemical models suggest that substantial amounts of l iquid hydrocarbons may exist near or on the surface: the most plausibl e model of Titan's surface therefore is an icy one, with lakes or smal l seas of hydrocarbons (principally ethane), many in impact craters. M edium-sized craters will have central peaks, while large craters may u ndergo viscous relaxation, their centres doming upwards, to push the l iquids into an annulus, thereby for-ming a ring lake. Additionally, cr aters with central pits may form ''bullseye'' lakes. The large tidal e ffects of Saturn on such lakes will affect their shape, distorting rin gs into horseshoes, and may also cause erosive migration.