SIMULATED RUNOFF-RESPONSE TO METHANE PRECIPITATION ON TITAN USING A PHYSICALLY-BASED MODEL

Evidence has revealed that Titan, the largest of Saturn’s moons, has a dense atmosphere and experiences a hydrologic cycle similar to that on Earth, with hydrocarbons such as methane replacing water as the primary liquid component. Lakes and fluvial features have been identified on the surface of Titan, yet the dynamics of its methane cycle remain difficult to monitor. The simulation-based effort reported here relies on present understanding of the physics of fluid flow on Earth to inform simple hypothesis testing about the factors controlling runoff-response to methane precipitation on Titan. This study employs the Integrated Hydrology Model (InHM), a physically-based numerical model of fully-coupled surface/subsurface fluid flow. InHM has been applied extensively for simulating rainfall-runoff processes for a variety of terrestrial environmental conditions over a wide range of spatial and temporal scales. Although little is known about the frequency, duration, and intensity of methane precipitation on Titan and the material properties of the moon’s rocky and icy surface, estimates of temperatures and the gravitational field on Titan can be used to estimate the density and viscosity of liquid methane there. Using well-studied experimental catchments on Earth as a starting point for model parameterization, the individual and combined influence of gravity, density, and viscosity on runoff response are demonstrated using alternative simulation scenarios for a range of Earth and Titan-like conditions. In general, the lower gravitational acceleration combined with greater fluid density and viscosity result in considerably less infiltration and more runoff for the Titan-like scenarios when compared to simulated (and observed) rainfall-runoff processes on Earth. Physics-based hydrologic response simulation has proven a useful tool for understanding landscape evolution on Earth and therefore could also be useful for understanding geomorphic processes on Titan such as the erosion of craters.