Cryovolcanoes, or ice volcanoes, erupt molten ices of different varieties (water, methane, ammonia and so on) instead of molten rocks, as happens on Earth. As such, they are present in the cold bodies of the outer Solar System such as icy moons. The existence of cryovolcanoes on Titan is still a matter of some debate. We have observed flow morphologies, but they can be difficult to interpret unambiguously as volcanic, as opposed to fluvial, and we know that Titan has fluvial activity. However, when the data for the Sotra Patera region of Titan were analysed, many of us concluded that this region, at least, was volcanic in origin.
This Cassini radar image of the area, obtained during the T25 and T28 Titan flybys at the beginning of 2007, is a perfect example of Cassini instruments working in synergy. It combines two Synthetic Aperture Radar images, which are used to reconstruct the topography with a digital elevation model (shown here with a vertical exaggeration of 10:1), with Visual and Infrared Mapping Spectrometer (VIMS) data, which show compositional differences in false colour (see a movie for the whole region at http://photojournal.jpl.nasa.gov/catalog/PIA13695).
The image shows one of the tallest peaks on Titan, Doom Mons, which is ~70 km in diameter and 1.45 ± 0.20 km high. Doom Mons is adjacent to the deepest depression so far found on Titan, Sotra Patera, an elongated pit ~30 km in diameter and 1.7 ± 0.2 km deep. These features, and the surrounding flow-like features around them (called Mohini Fluctus), have been interpreted as cryovolcanic. They are shown here in shades of green and yellow from VIMS data, whereas the dune fields are in blue. This colour difference indicates that the dunes have a different composition from the candidate cryovolcanic materials.