Dissolution on Saturn's Moon Titan: A 3D Karst Landscape Evolution Model
Résumé
Titan is an Earth-like world possessing a nitrogen-rich atmosphere that covers a surface with signs of lacustrine
(lakes, seas, depressions), fluvial (channels, valleys) and aeolian (dunes) activity [1]. The chemistry implied in the
geological processes is, however, strikingly different from that on Earth. Titan’s extremely cold environment (T ∼
-180◦C) allows water to exist only under the form of icy "bedrock". The presence of methane as the second major
constituent in the atmosphere, as well as an active nitrogen-methane photochemistry, allows methane and ethane to drive a hydrocarbon cycle similar to the terrestrial hydrological cycle. A plethora of organic solids, more or less soluble in liquid hydrocarbons, is also produced in the atmosphere and can lead, by atmospheric sedimentation over geological timescales, to formation of some kind of organic geological sedimentary layer.
Based on comparisons between Titan’s landscapes seen in the Cassini spacecraft data and terrestrial analogues,
karstic-like dissolution and evaporitic crystallization have been suggested in various instances to take part in the
landscape development on Titan. Dissolution has been invoked, for instance, for the development of the so-called "labyrinthic terrain", located at high latitudes and resembling terrestrial cockpit or polygonal karst terrain. In this work, we aim at testing this hypothesis by comparing the natural landscapes visible in the Cassini/RADAR
images of Titan’s surface, with those inferred from the use of a 3D Landscape Evolution Model (LEM) based on
the Channel-Hillslope Integrated Landscape Development (CHILD) [2] modified to include karstic dissolution
as the major geological process [3]. Digital Elevation Models (DEMs) are generated from an initial quasi-planar
surface for a set of dissolution rates, diffusion coefficients (solute transport), and sink densities of the mesh. The
landscape evolves over millions of years. Synthetic SAR images are generated from these DEMs in order to be
compared with Titan’s landforms seen in the Cassini SAR data. Inference on the possible thickness and degree of
maturation of the Titan karst will be discussed.