PASADENA, July 31: At least one of many large lake-like features on Saturn’s moon Titan studied by the international Cassini spacecraft contains liquid hydrocarbons, making it the only body in the solar system, besides Earth, known to have liquid on its surface, Nasa has said.

Scientists positively identified the presence of ethane, according to a statement from Nasa’s Jet Propulsion Laboratory (JPL) in Pasadena, which manages the Cassini mission exploring Saturn, its rings and moons.

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-kilometre voyage. Cassini has made more than 40 close flybys of Titan.

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 than North America’s Lake Ontario.

Scientists had theorised that Titan might have oceans of methane, ethane and other hydrocarbons, but Cassini found hundreds of dark, lake-like features instead, and it was not known at first whether they were liquid or dark, solid material, JPL’s statement said.

“This is the first observation that really pins down that Titan has a surface lake filled with liquid,” Bob Brown, team leader of Cassini’s visual and mapping instrument, said in the statement. Brown is with the University of Arizona, Tucson.

Larry Soderblom, a scientist with the US Geological Survey in Flagstaff, Arizona, said: “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 have 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.

The mission is a project of Nasa, the European Space Agency and the Italian Space Agency.

—Agencies