1. ^*Department of Astronomy, PO Box 112055, University of Florida, Gainesville, Florida 32611-2055, USA
2. ^†Laboratory for Planetary Studies, Cornell University, Ithaca, New York 14853, USA

Abstract

THERMODYNAMIC and photochemical arguments^1–4 suggest that Titan, the largest satellite of Saturn, has a deep ocean of liquid hydrocarbons. At visible wavelengths, Titan's surface is obscured by a thick stratospheric haze, but radar observations^5–7 have revealed large regions of high surface reflectivity that are inconsistent with a global hydrocarbon ocean. Titan's surface has also been imaged at infrared wavelengths^8–10, and the highest-resolution data (obtained by the Hubble Space Telescope) show clear variations in surface albedo and/or topography¹⁰. The natural interpretation of these observations is that Titan, like the Earth, has continents and oceans. But Titan's high orbital eccentricity poses a problem for this interpretation, as the effects of oceanic tidal friction would have circularized Titan's orbit for most configurations of oceans and continents^1,11. Here we argue that a more realistic topography, in which liquid hydrocarbons are confined to a number of disconnected seas or crater lakes, may satisfy both the dynamical and observational constraints.