Topographic Constraints on the Evolution and Connectivity of Titan's Lacustrine Basins

Abstract:

The topographic information provided by Cassini RADAR Altimetry, SAR Topography, and stereo radargrammetry has opened new doors for Titan research by allowing the quantitative analysis of morphologic form. Using these datasets, we investigate the three-dimensional morphology of Titan’s lacustrine basins in order to address their interconnectivity and provide observables that will constrain plausible formation mechanism. Using altimetry measurements, we will show that the liquid elevations of Titan’s maria share, to within measurement error, the same equipotential surface. The liquid elevations of several smaller lakes, however, are several hundreds above sea level, suggesting that they exist in isolated or perched basins. However, within a given topographic basin, the floor elevations of empty lake floors are always higher than the local liquid elevation, suggesting local subsurface connectivity. Furthermore, basins with floors closer to the local phreatic surface appear brighter to both nadir and off-nadir microwave observations than those that are more elevated, indicating a potential change in composition.

The majority of Titan’s lakes reside in sharp edged depressions whose planform curvature suggests expansion through uniform scarp retreat. Many, but not all, of these basins exhibit flat floors and hundred-meter scale raised rims that present a challenge to proposed formation models. The basins are often topographically closed with no evidence for inflow or outflow channels at the 300 m resolution of Cassini SAR images. The implications of these observations will be discussed in the context of common basin formation models, including karst, organic diapirs, periglacial processes (e.g., pingos, thaw lakes, and kettle holes), cryovolcanic processes (e.g., laccoliths, maars, and calderas), craters, gas pockmarks, and sublimation. We will conclude that dissolution (e.g., karst) or pressurized gas release (e.g., gas pockmarks) mechanisms can best match the observed constraints, but that challenges still exist in the interpretation of formation processes and materials.