Are the basins of Titan's Hotei Regio and Tui Regio sites of former low latitude seas?

Abstract

Features observed in the low‐latitude basins of Hotei Regio and Tui Regio on Titan have attracted the attention of the Cassini‐era investigators. At both locations, Visual Infrared Mapping Spectrometer (VIMS) observed isolated 5‐μm bright ∼500 km wide features described as lobate in shape. Several studies have proposed that these materials are cryo‐volcanic flows. We propose an alternative explanation. Recently published topographic profiles across Hotei Regio and Tui Regio indicate these features appear to occur in large regional basins, at least along the direction of the profiles. Cassini Synthetic Aperture Radar (SAR) images show that the terrains surrounding both topographically low‐lying 5‐μm bright features exhibit fluvial networks that appear to converge into the probable basins. The 5‐μm bright features themselves correspond to fields of discrete radar‐bright depressions whose bounding edges are commonly rounded and cumulate in planform in SAR images. These fields of discrete radar‐bright depressions strongly resemble fields of features seen at Titan's high latitudes identified as dry lakes. Thus the combination of (1) the resemblance to high‐latitude dry lakes, (2) location in the centers of regional depressions, and (3) convergence of fluvial networks are inferred by us to best explain the features of Hotei Regio and Tui Regio as sites of paleolake clusters (and perhaps former, now dry seas). These low‐latitude paleolake clusters or former seas, if real, may be evidence of substantially larger inventories of liquid alkanes in Titan's past.