Channels on Titan: an Examination of Data Effects and a Comparison with Earth Analogs

Titan, Saturn's largest moon, is the only extraterrestrial body in the solar system known to have an active hydrological system. Cassini RADAR (λ ~2.2cm) and the Huygens descent camera (visible wavelengths) have revealed complex channel networks on the moon's surface, and with the complete datasets from the Cassini-Huygens mission, an updated map of Titan's channels is timely. We have produced a map of all channels on Titan observable in the complete Cassini synthetic aperture radar (SAR) dataset, excluding potential near- or sub-resolution channels in labyrinth terrains. Titan's channel systems, as seen in the Cassini SAR data (with resolutions of 350 m/pixel to 1.7 km/pixel), bear a striking resemblance to the largest river networks on Earth in both morphology and visibility in SAR data. To assess the validity of our Titan mapping, we chose three terrestrial river networks with similarities in scale and morphology to those on Titan, and mapped them in high resolution (2.5 m/pixel) visible images, medium resolution (10 m/pixel) visible and SAR (λ ~5.4 cm) images, and "Cassini quality" (330 m/pixel) downgraded SAR images. We calculated channel metrics for each mapped channel network to determine which metrics were resolution-invariant, and to gain a better understanding of how the low-resolution Cassini SAR data might bias our results and interpretations. We found that drainage density and Shreve stream order varied consistently with the resolution at which the channels were mapped, and that network geometry and the average branching angle of lower-order (smaller) links changed appreciably with resolution, while the average branching angle of higher-order (larger) links did not. This analysis suggests that interpretations of Titan's geology based on traditional channel metrics may be valid only at large (kilometer) spatial scales, and that tectonic activity may not be closely correlated with the presence of observed rectangular networks.