Images returned during Cassini's recent flyby of Titan showcaptivating evidence of what appears to be a large shoreline cuttingacross the smoggy moon's southern hemisphere. Hints that this area wasonce wet, or currently has liquid present, are evident.
"We've been looking for evidence of oceans or seas on Titan for sometime. This radar data is among the most telling evidence so far for ashoreline," said Steve Wall, radar deputy team leader from NASA's JetPropulsion Laboratory, Pasadena, Calif.
The images show what looks like a shoreline dividing a distinctbright and dark region roughly 1,700 kilometers long by 170 kilometerswide (1,060 by 106 miles). Directly to the right of a bright andpossibly rough area is one that is very dark and smooth.
"This is the area where liquid or a wet surface has most likely beenpresent, now or in the recent past, said Wall. "Titan probably hasepisodic periods of rainfall or massive seepages of liquid from theground."
The brightness patterns in the dark area indicate that it may oncehave been flooded with liquid that may now have partially receded.Bay-like features also lead scientists to speculate that thebright-dark boundary is most likely a shoreline.
"We also see a network of channels that run across the brightterrain, indicating that fluids, probably liquid hydrocarbons, haveflowed across this region," said Dr. Ellen Stofan, Cassini associateradar team member from Proxemy Research, Laytonsville, Md.
Taken together with the two other radar passes in October 2004 andFebruary 2005, these very high resolution images have identified atleast two distinct types of drainage and channel formation on Titan.Some channels in images from this pass are long and deep, with angularpatterns and few tributaries, suggesting that fluids flow over greatdistances. By contrast, others show channels that form a denser networkthat might indicate rainfall.
Dr. Larry Soderblom with the U.S. Geological Survey in Flagstaff,Ariz., said, "It looks as though fluid flowed in these channels,cutting deeply into the icy crust of Titan. Some of the channels extendover 100 kilometers (60 miles). Some of them may have been fed bysprings, while others are more complicated networks that were likelyfilled by rainfall."
Titan has an environment somewhat similar to that of Earth beforebiological activity forever altered the composition of Earth'satmosphere. The major difference on Titan, however, is the absence ofliquid water, and Titan's very low temperature. With a thick,nitrogen-rich atmosphere, Titan was until recently presumed to holdlarge seas or oceans of liquid methane. Cassini has been in orbitaround Saturn for a year and has found no evidence for these large seas.
Cassini encountered an anomaly with one of two solid-state recordersduring the Sept. 7 close flyby, resulting in some data not beingrecorded. Half of the data from the flyby was received, much to thedelight of anxious scientists. The spacecraft team is troubleshootingthe cause, and early indications point to a software problem that wouldbe correctable with no long-term impacts.
This was Cassini's eighth out of 45 Titan flybys planned in thenominal four-year tour. The next radar pass will be Oct. 26 when theteam will focus on the Huygens probe landing site close to the equator.
The Cassini-Huygens mission is a cooperative project of NASA, theEuropean Space Agency and the Italian Space Agency. JPL, a division ofthe California Institute of Technology in Pasadena, manages theCassini-Huygens mission for NASA’s Science Mission Directorate,Washington. The Cassini orbiter was designed, developed and assembledat JPL. The radar instrument team is based at JPL, working with teammembers from the United States and several European countries.
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