Radar imaging data from the Cassini flyby of Titan provide convincing evidence for large bodies of liquid. This image gives a taste of what Cassini saw. Intensity in this colorized image is proportional to how much radar brightness is returned, or more specifically, the logarithm of the radar backscatter cross-section. The colors are not a representation of what the human eye would see.

The lakes, darker than the surrounding terrain, are emphasized here by tinting regions of low backscatter in blue. Radar-brighter regions are shown in tan. The strip of radar imagery is foreshortened to simulate an oblique view of the highest latitude region, seen from a point to its west.

Credits: NASA/JPL/USGS

Scientists have speculated that liquid methane or ethane might form lakes on Titan, particularly near the somewhat colder polar regions. In the images, a variety of dark patches, some with channels leading in or out of them, appear. The channels have a shape that strongly implies they were carved by liquid. Some of the dark patches and connecting channels are completely black, that is, they reflect back essentially no radar signal, and hence must be extremely smooth. In some cases rims can be seen around the dark patches, suggesting deposits that might form as liquid evaporates. The abundant methane in Titan's atmosphere is stable as a liquid under Titan conditions, as is its abundant chemical product, ethane, but liquid water is not.

For all these reasons, scientists interpret the dark areas as lakes of liquid methane or ethane, making Titan the only body in the solar system besides Earth known to possess lakes. Because such lakes may wax and wane over time, and winds may alter the roughness of their surfaces, repeat coverage of these areas should test whether these are indeed bodies of liquid.

Credits: NASA/JPL

The lake at the left is reminiscent both in form and scale of the flooded drainage system, Lake Powell in Utah and Arizona. However, the Titan lake has been filled with liquid methane and ethane rather than water. In the lake at right, older terrain may have been deeply cut by river valleys before it was flooded by the embaying lake.

Credits: NASA/JPL

The large dark patch seen on this image, at high latitudes surrounding Titan's north pole, is most likely a hydrocarbon lake. Several dark channels can be seen; the longest one at the left meanders over almost 100 kilometres, and appears to drain into the lake. Some dark channels are remarkably straight, suggesting possible faulting in the subsurface.

Credits: NASA/JPL