Dissolution on Titan and on Earth: Towards the Age of Titan's Karstic-like Landscapes

Abstract:

Titan's polar surface is dotted with hundreds of lacustrine depressions. Their morphology suggests that their development would be associated to karstic-like processes, involving Titan's liquids (methane, ethane) dissolving the solid surface, presumably composed of organics and ices. In the present work, we test whether or not surface dissolution could be a major landshaping process on Titan using a solutional denudation rates model. The model is based on thermodynamics (solute solubility in solvents) and climatic (temperature, precipitation rates) parameters and has already been used to describe the dissolution of carbonates in karstic areas on Earth. It allows inference of rough formation timescales for topographic depressions of a given depth, developed by chemical erosion only. We computed and compared the denudation rates of pure solid organics in liquid hydrocarbons and of minerals in liquid water over Titan and Earth timescales. We then investigated the denudation rates of superficial organic layers in liquid methane over one Titan year. At this timescale, such a layer on Titan would behave like salts or carbonates on Earth depending on its composition, which means that dissolution processes would likely occur but would be 30 times slower on Titan compared to the Earth due to the seasonality of methane precipitation. Assuming that Titan's past climatic conditions remained close to the present ones, and assuming an average depth of 100 m for Titan's lacustrine depressions, these could have developed in a few tens of millions of years at polar latitudes higher than 70°N and S, and a few hundreds of million years at lower polar latitudes. The ages determined are consistent with the youth of the surface (<1 Gyr) and the repartition of dissolution-related landforms on Titan.