This image of Saturn's largest moon, Titan, obtained by Cassini's radar instrument during a near-polar flyby on Feb. 22, 2007, features dunes and lakes, one of which is larger than any lake on Earth and could be legitimately called a sea. First discovered by Cassini's radar in July 2006 (see Lakes on Titan), Titan's lakes are thought to consist of liquid methane and ethane.
The image runs from southern latitudes, starting at 32 degrees south, 55 degrees west, where we see featureless terrain with bright streaks, heading 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 (see Titan Features and Interactions). In one case, the dunes wrap around an unusual rose-shaped structure, approximately 70 kilometers (40 miles) across. Near the spacecraft's closest approach (33 degrees north, 28 degrees west), where the swath is at its narrowest, the terrain is dark and mottled, with occasional bright outcrops and fine dunes. As we continue to head north, we see the first signs of the action of liquids -- fine channels and canyon-like structures. Later, depressions can be seen. These are similar to those seen in the lake region and are interpreted as volcanic calderas or drained lakes. 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, which is closest to the pole, contains by far the largest lakes observed by Cassini's radar to date. Part of the first of these was seen during a previous flyby (see Titan's Great Lakes?), and is fed by a long river -- over 200 kilometers (120 miles) in length, and hundreds of meters to over 1 kilometer (0.6 miles) in width - running through what appears to be a flood plain. The lake's bright, jutting shoreline indicates that old, eroded landforms may have been flooded. The end of the next lake was also observed before (see Lakes and More lakes), appearing to be, in both form and scale, similar to Lake Powell, a flooded drainage system in Utah and Arizona. We can now see that this lake on Titan connects via a relatively narrow channel to a much larger (at least 45,000 square kilometers or 17,000 square miles) lake, containing a large (approximately 12,000 square kilometers or 4,600 square miles) island or peninsula (see Titan: Larger and Larger Lakes). The last part of the image passes close to the pole (86 degrees north, 290 degrees 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 kilometers (39,000 square miles), which is greater in extent than one of the largest lakes on Earth, Lake Superior (82,000 square kilometers or 32,000 square miles), and covers a greater fraction of Titan than the largest terrestrial inland sea, the Black Sea. The Black Sea covers 0.085 percent of the surface of the Earth; this newly observed body on Titan covers at least 0.12 percent of the surface of Titan. Because of its size, scientists are calling this a sea.
The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA's Science Mission Directorate, Washington, D.C. The Cassini orbiter was designed, developed and assembled at JPL. The radar instrument was built by JPL and the Italian Space Agency, working with team members from the United States and several European countries.
For more information about the Cassini-Huygens mission visit http://saturn.jpl.nasa.gov/home/index.cfm.