Radar aboard NASA's Cassini spacecraft got images of what appears to be a large shoreline cutting across Saturn moon Titan's southern hemisphere. Mission scientists indicated on Friday that this area was once wet, or currently has liquid present.

Astronomers have been seeking for a long time traces of a methane sea or ocean on Titan. These radar images are among the most telling evidence so far for a shoreline, said Steve Wall, Cassini radar scientist at NASA's Jet Propulsion Laboratory (JPL) based in Pasadena, California.

The images show what looks like a shoreline dividing a distinct bright and dark region roughly 1,700 km long 170 km wide.

"This is the area where liquid or a wet surface has most likely been present, now or in the recent past," Wall said.

"Titan probably has episodic periods of rainfall or massive seepages of liquid from the ground."

The brightness patterns in the dark area indicated that it may once have been flooded with liquid that may now have partially receded. Bay-like features also led scientists to speculate that the bright-dark boundary is most likely a shoreline.

Mission scientists also saw a network of channels that run across the bright terrain, indicating that fluids, probably liquid hydrocarbons, have flowed across this region, according to Ellen Stofan, a Cassini radar team member.

Taken together with the two other radar passes in October 2004 and February 2005, these very high resolution images have identified at least two distinct types of drainage and channel formation on Titan.

Some channels are long and deep with angular patterns and few tributaries, suggesting that fluids flow over great distances. By contrast, others show channels that form a denser network that might indicate rainfall.

It looks as if fluid flowed in these channels, cutting deeply into the icy crust of Titan. Some of the channels extend over 100 km, some of them may have been fed by springs, while others are more complicated networks that were likely filled by rainfall, scientists said.

Titan has an environment somewhat similar to that of Earth, while the major differences are the absence of liquid water and very low temperature, astronomers said.

With a thick, nitrogen-rich atmosphere, Titan was until recently presumed to hold large seas or oceans of liquid methane. But Cassini has found no credible evidence yet for these large seas since it was flying around Saturn for a year.

Cassini encountered an anomaly with one of two solid-state recorders during the Sept. 7 close flyby, resulting in some data not being recorded. But half of the data from the flyby was received, delighting anxious scientists.

The spacecraft team is troubleshooting the cause, and early indications point to a software problem that would be correctable with no long-term impacts, according to the JPL.

Source: Xinhua