WASHINGTON (Reuters) -- Could Saturn's moon Titan be a land of lakes?

A new image captured by the Cassini spacecraft indicates that it just might -- though the possible lake in question could be filled with liquid methane rather than water, NASA said on Tuesday.

The putative lake appears in a Cassini image of Titan's south polar region, a well-defined but irregularly shaped dark spot with smooth, shore-like boundaries unlike anything previously seen on this Saturn satellite.

It is about 145 miles by 45 miles (234 km by 73 km), about the size of Lake Ontario on the U.S.-Canadian border, Cassini scientists said in a statement.

"This feature is unique in our exploration of Titan so far," said Elizabeth Turtle, Cassini imaging team associate at the University of Arizona. "Its perimeter is intriguingly reminiscent of the shorelines of lakes on Earth that are smoothed by water erosion and deposition."

It lies in Titan's cloudiest region, where astronomers believe there might be methane rain.

"It's possible that some of the storms in this region are strong enough to make methane rain that reaches the surface," said Cassini team member Tony DelGenio of NASA's Goddard Institute for Space Studies in New York.

Because of extreme cold temperatures on Titan, the liquid methane could take a long time to evaporate, which would let a methane-filled lake last for a long while, DelGenio said.

The dark splotch might also be a former lake that has now dried, or a broad depression filled with dark, solid hydrocarbons, the scientists said.