Morphological evidence that Titan's southern hemisphere basins are paleoseas

Cassini has shown that modern liquid bodies are largely restricted to North polar latitudes ( > 55°) with a comparatively small volume of liquid in the southern hemisphere. This dichotomy has previously been attributed to Saturn's current orbital configuration, but if correct, the configuration is transient and southern depositional basins equivalent in volume to the northern seas are required. In the South polar region, we have identified four dry broad depressions, equivalent in area to the northern seas. Morphologic and topographic data suggest that they represent paleoseas that were filled during an earlier epoch more favorable to the accumulation of southern liquids. All four basins are characterized by topographically low, SAR-dark plains, along with dissected margins that mark putative paleo-shorelines. These characteristics imply that these depressions represent depositional basins. Topographically, the basins have a combined volume that is  ∼ 3 times greater than the northern seas, sufficiently large to contain all of the northern liquids. A lack of evidence for 5-µm bright material, interpreted as evaporite, challenges our interpretations in the absence of efficient removal or burial mechanisms. The long time scale over which fluids migrate, however, suggests that any deposits have ample time to be altered/removed.