INVESTIGATING TITAN’S TECTONIC HISTORY FROM MORPHOLOGY, ORIENTATION, AND ELEVATION OF RIDGES SEEN IN CASSINI RADAR IMAGERY

Synthetic Aperture RADAR images captured by the Cassini spacecraft reveal linear to arcuate chains of mountains across much of the surface of Saturn’s moon Titan. The longest of these ridges (up to hundreds of km) occur in Titan’s equatorial regions, and likely have several hundred meters of vertical relief. Due to their morphological similarity to fold-thrust belts on Earth, these have been attributed to horizontal compression, possibly caused by solid-state convection in Titan’s outer ice shell and global contraction. Titan’s ridges lie preferentially at higher elevations and dominantly trend east-west, although some individual ridge orientations vary significantly.

In order to further investigate structural trends discussed by earlier workers, we measured lengths and orientations of 532 individual ridge crests in the region between 30° N, 240° W and 30° S, 150° W where the highest density of well-imaged ridges are found. The ridge segments range in length from 2 km to >150 km with an average of 23 km, and have a mean strike of 104° with a standard deviation of 29.3°. The orientations of shorter, widely-spaced ridge segments are more variable, and some appear to align along general north-south trends, although measurements on small features have greater uncertainty due to limited imagery resolution. Additionally, at least one set of east-striking ridges appears to form an en-echelon array along a northeast-trending lineament which traverses a broad topographic high and seems to exert significant control on the orientation of surrounding linear dunes.

These results are generally consistent with the overall east-west trend noted by others, supporting the conclusion that ridges formed under a global stress field with maximum principal stress directed north-south, though the causes are not well understood. Based on the more heavily cratered and eroded morphology of the mountainous Xanadu region, some have suggested multiple episodes of tectonism on Titan. Though still largely enigmatic, the isolated ridge segments with anomalous orientations and the long-wavelength topographic feature noted above may be remnants of features formed by an earlier tectonic event and later modified and partially buried by erosion. Alternatively, they may simply represent local complexities in the broader stress regime.