Titan’s Great Lakes
Newly assembled radar images from the Cassini spacecraft provide the best view of the hydrocarbon lakes and seas on the north pole of Saturn’s moon Titan, while a new radar image reveals that Titan’s south polar region also has lakes. The images provide new insight into the cycling of hydrocarbons on Titan, which is in some ways similar to the water cycle on Earth. Titan is a uniquely active environment in the Solar System and is the only known moon with a significant atmosphere. Some scientists believe that Titan might, in some ways, resemble aspects of the early Earth and could provide clues about how important precursor molecules for the origin of life on our planet were formed.
Images from the southern region of Titan were beamed back after an Oct. 2 flyby in which a prime goal was the hunt for lakes at the south pole.
A new mosaic image, created by stitching together radar images from seven Titan flybys over the last year and a half, shows a north pole pitted with giant lakes and seas, at least one of them larger than Lake Superior.
Approximately 60 percent of Titan’s north polar region above 60 degrees latitude has been mapped by Cassini’s radar instrument. About 14 percent of the mapped region is covered by what scientists interpret as liquid hydrocarbon lakes.
"This is our version of mapping Alaska, the northern parts of Canada, Greenland, Scandinavia and Northern Russia," said Rosaly Lopes, Cassini radar scientist at NASA’s Jet Propulsion Laboratory, Pasadena, Calif. "It’s like mapping these regions of Earth for the first time."
Lakes and seas are very common at the high northern latitudes of Titan, which is in winter now. Scientists say it rains methane and ethane there, filling the lakes and seas. These liquids also carve meandering rivers and channels on the moon’s surface. Now Cassini is moving into unknown territory, the south pole of Titan. "We wanted to see if there are more lakes present there and, sure enough, there they are, three little lakes smiling back at us. Titan is indeed the land of lakes and seas," said Lopes. "It will be interesting to see the differences between the north and south polar regions."
It is now summer at Titan’s south pole. A season on Titan lasts nearly 7.5 years, one quarter of a Saturn year, which is 29.5 years long. Monitoring seasonal change helps scientists understand the processes at work there.
Scientists are making progress in understanding how the lakes may have formed. On Earth, lakes fill low spots or are created when the local topography intersects a groundwater table. Lopes and her colleagues think that the depressions containing the lakes on Titan may have formed by volcanism or by a type of erosion (called karstic) of the surface, leaving a depression where liquids can accumulate. Karstic lakes are common on Earth. For example in parts of Minnesota and central Florida there are hundreds of such lakes.
"The lakes we are observing on Titan appear to be in varying states of fullness, suggesting their involvement in a complex hydrologic system akin to Earth’s water cycle. This makes Titan unique among the extra-terrestrial bodies in our solar system," said Alex Hayes, a graduate student who studies Cassini radar data at the California Institute of Technology in Pasadena.
"The lakes we have seen so far vary in size from the smallest observable, approximately 1 square kilometer (0.4 square miles), to greater than 100,000 square kilometers (40,000 square miles), which is slightly larger than the Great Lakes in the Midwestern U.S.," Hayes said. "Of the roughly 400 observed lakes, 70 percent of their area is taken up by large "seas" greater than 26,000 square kilometers (10,000 square miles)."
Future radar flybys will image closer to the southern pole and are expected to show more lakes.