A dark, marking feature observed recently on Saturn's moon Titan by the Cassini spacecraft may be a hydrocarbon lake, scientists working with US National Aeronautics and Space Administration (NASA) reported Tuesday.

The feature lies in Titan's cloudiest region, which is presumably the most likely site of recent methane rainfall. This, coupled with the shore-like smoothness of the feature's perimeter, makes it hard for scientists to resist speculation about what might be filling the lake, if it indeed is one.

"I'd say this is definitely the best candidate we've seen so far for a liquid hydrocarbon lake on Titan," said Alfred McEwen, Cassini imaging team member and a professor at the University of Arizona, Tucson.

The suspected lake area measures 234 kilometers long by 73 kilometers wide, about the size of Lake Ontario on the US Canadian border, according to NASA's Jet Propulsion Laboratory (JPL).

This feature is unique that its perimeter is intriguingly reminiscent of the shorelines of lakes on Earth that are smoothed by water erosion and deposition, indicating that some of the storms in this region are strong enough to make methane rain that reaches Titan's surface.

Given Titan's cold temperatures, it could take a long time for any liquid methane collecting on the surface to evaporate, scientists said. Therefore, it might not be surprising for a methane-filled lake to persist.

Despite earlier predictions, no definitive evidence for open bodies of liquid has been found on Titan. Cassini has not yet been in a favorable position for using its cameras to check for glints from possible surface liquids in the south polar region.

But as the seasons change over a few years, the convective clouds may migrate northward to lower latitudes, when the Cassini cameras will be able to record changes in the appearance of the surface, the JPL said.

An alternate explanation is that this feature was once a lake, but has since dried up, leaving behind dark deposits.

Another possibility is that the lake is simply a broad depression filled by dark, solid hydrocarbons falling from the atmosphere onto Titan's surface. In this case, the smooth outline might be the result of a process unrelated to rainfall, such as a sinkhole or a volcanic caldera.

Whatever this lake-like feature turns out to be, it is only one of many puzzles of Titan as the Cassini program continues reconnaissance of its surface over the next few years, scientists noted.

Thirty-nine more Titan flybys are planned for Cassini's prime mission. In future flybys the science teams will search for opportunities to observe the lake feature again and to look for mirror-like reflections from smooth surfaces elsewhere, which would strongly support the presence of liquids.

Source: Xinhua