Evolution of Titan's coupled Ocean-Atmosphere system and interaction of ocean with bedrock

Abstract

A recent model for the surface state of Titan proposes a liquid ethane-methane-molecular nitrogen layer of order one kilometer thick which because of stratospheric methane photolysis has become increasingly ethane-rich with time (1). We explore the interaction of such an ocean with the underlying "bedrock" of Titan (assumed to be water-ice or ammonia hydrate) and with the primarily nitrogen atmosphere. It is concluded that although modest exchange of oceanic hydrocarbons with enclathrated methane in the bedrock can in principle occur, it is unlikely for reasonable regolith depths. The surprisingly high solubility of water ice in liquid methane (2) implies that topographic features on Titan of order 100 meter in height can be eroded away on a time scale ≾10^9 years. The large solubility difference of N_2 in methane versus ethane implies that the ocean composition is a strong determinant of atmospheric pressure; a simple radiative model of the Titan atmosphere is employed to demonstrate that significant surface pressure and temperature changes can occur as the oceanic composition evolves with time.