HYDROLOGY-BASED UNDERSTANDING OF ONTARIO LACUS ON TITAN'S SOUTH POLE

Ontario Lacus is the largest, presently filled lake at the South Pole of Titan. Many other large basins lower than Ontario in elevation also exist at the South Pole but are empty. To find what sets Ontario apart from those empty basins, we analyze the hydrology of Ontario Lacus. We measure the spatial extent of the catchment basins using topography data. The catchment areas (~4.6 million km²) contributing to Ontario Lacus (55,342 km²) extend much further than that of other basins, as far as the southern mid-latitudes. Clouds in southern mid and high latitudes have been observed by Cassini VIMS which indicate possible precipitation in those regions. Precipitation in southern mid-latitudes coupled with the topographical lows that drain into Ontario Lacus could be the reason behind it being filled. The mass conservation calculations indicate that if runoff is the only contributor to the lake volume, the lake might still be filled in entirety. In order to get furthermore clues we also derive a non-linear relationship between catchment areas and the stream length on Titan based on Hack's Law. The law takes a similar form in Titan like conditions as well. This provides another similarity between liquid water driven drainage networks on Earth and those on Titan.