GANDALF COLLES AS A CANDIDATE CRYOVOLCANIC FEATURE NEAR SELK CRATER, TITAN

Gandalf Colles is a high-backscatter feature in Cassini’s Synthetic Aperture Radar (SAR) data, located at the margin of the Shangri-La dune sea and Caladan Planitia on Titan. It is situated 580 km to the NW of Selk Crater, the target of the upcoming Dragonfly mission. Initially considered the type feature for hummocky terrain on Titan, a re-examination has revealed several spectral and morphological signatures consistent with a cryovolcanic origin.

Gandalf Colles presents as a high backscatter feature roughly 110 km across. The interior region exhibits a uniform mottling that could be the result of knobby or hummocky relief. To the north lies an area that appears to have a flow front boundary displaying similar morphologies to that those of the lobate flow Mohini Fluctus, associated with the putative Doom Mons cryovolcano. Dark sand materials interpreted to flow from the SW diverge around the central part of Gandalf Colles and bisect the feature, with a clear set of linear dunes present across the southern edge. This divergence suggests that Gandalf Colles is a topographic obstacle. Cassini RADAR altimetry data indicated Gandalf’s margin is elevated roughly 50 m above the surrounding terrain, although the central part of Gandalf Colles was not measured.

Gandalf Colles has significantly lower microwave emissivity values compared to the surrounding terrain. The lower emissivity values are consistent with large exposures of water ice materials, in contrast to the surrounding organic dunes and plains. Infrared data are consistent with Gandalf Colles having a composition similar to the rim of Afekan Crater –interpreted as a mixture of icy materials and organics. In addition, SAR data indicates low backscatter pit-like features that could be interpreted as collapsed lava tube pits that extend from the central are of Gandalf towards the distal flow margin.

When compared to the Doom Mons cryovolcanic candidate for Titan, Gandalf Colles exhibits slightly weaker morphological evidence, but much stronger spectral and microwave emissivity evidence. Overall, the central high backscatter region of Gandalf is consistent with a large nearly flat but mottled exposure of extruded water ice, with flow margins at the periphery that have been partially invaded by dune materials. This combination of features makes Gandalf Colles a compelling cryovolcanic candidate on Titan.