This image of Saturn’s largest moon, Titan, obtained by Cassini's radar instrument during a near-polar flyby on 22 February 2007, features dunes and lakes, one of which is larger than any lake on Earth and could be legitimately called a sea. Titan’s lakes are thought to consist of liquid methane and ethane.
The image runs from southern latitudes, starting at 32 ° South, 55 ° West. Featureless terrain with bright streaks heads north and slightly east through dune fields interspersed with exposed bright mounds. In places, the dunes wrap around the bright mounds, which suggests the mounds are raised. In one case, the dunes wrap around an unusual rose-shaped structure, approximately 70 kilometres across. Near the spacecraft’s closest approach (33 ° North, 28 ° West), where the swath is at its narrowest, the terrain is dark and mottled, with occasional bright outcrops and fine dunes. Heading north, the action of liquids – fine channels and canyon-like structures can be seen. Later, depressions interpreted as volcanic calderas or drained lakes can be seen. As the swath continues, these become more plentiful, and some are partly filled with dark material thought to be liquid hydrocarbons, hence lakes. In places, the lakes reside in what appear to be nested, near-circular depressions, reminiscent of nested calderas.
The final section of the swath, closest to the pole, contains by far the largest lakes observed by Cassini’s radar to date. The lake’s bright, jutting shoreline indicates that old, eroded landforms may have been flooded. This lake on Titan connects via a relatively narrow channel to a much larger (at least 45 000 square kilometres) lake, containing a large (approximately 12 000 square kilometres) island or peninsula. The last part of the image passes close to the pole (86 ° North, 290 ° East), before heading east and slightly south. At the end of the swath, we see the largest lake observed yet – at least 100 000 square kilometres, covering a greater fraction of Titan (0.12 percent of its surface) than the largest terrestrial inland sea, the Black Sea (0.085 percent of the Earth’s surface).