NASA scientists said Wednesday they had found liquid on Saturn's moon Titan, only the second body in the solar system after Earth to have fluid on its surface.

The groundbreaking discovery was made after analysis of instruments on the US-European Cassini probe, the spacecraft that has been orbiting Saturn since 2004 following a 3.5 billion-kilometer (2.2 billion miles) voyage.

NASA said in a statement that information from Cassini indicated that large lakes on Titan contained liquid hydrocarbons and ethane.

"This is the first observation that really pins down that Titan has a surface lake filled with liquid," said University of Arizona scientist Bob Brown, team leader of Cassini's visual and mapping instrument.

NASA said large dark areas on Titan's surface had been spotted during numerous close flybys of the moon. However until now it had not been possible to determine whether they were liquid or solids.

But scientists were able to conclude the areas were liquid after studying data from a Cassini instrument able to distinguish chemically different materials based on the way they absorb and reflect infrared light.

The visual and mapping instrument spotted a lake, Ontario Lacus, in Titan's south polar region during a flyby in December, NASA said. The lake is roughly 7,800 square miles, slightly bigger North America's Lake Ontario.

"Detection of liquid ethane confirms a long-held idea that lakes and seas filled with methane and ethane exist on Titan," said Larry Soderblom, a scientist with the US Geological Survey in Flagstaff, Arizona.

"The fact we could detect the ethane spectral signatures of the lake even when it was so dimly illuminated, and at a slanted viewing path through Titan's atmosphere, raises expectations for exciting future lake discoveries by our instrument."

Scientists ruled out the presence of water ice, ammonia, ammonia hydrate and carbon dioxide in Ontario Lacus.

The observations also suggest the lake is evaporating. It is ringed by a dark beach, where the black lake merges with the bright shoreline.

Launched in 1997, the Cassini-Huygens mission is the first devoted to the exploration of Saturn, and is a joint mission by NASA and the European Space Agency.