The theory that vast seas of liquid methane or ethane exist on Saturn's moon Titan has been bolstered by evidence recently gathered by a passing space probe, researchers say.

Among the details observed by the Cassini-Huygens spacecraft is a sea larger than any of the Great Lakes, scientists at the U.S. National Aeronautics and Space Administration (NASA) said late Tuesday.

Cassini's radar sensor took images of dark features near the frigid moon's north pole that were much larger than any previously seen on Titan. The largest one seen was at least 101,000 square kilometers in size, the researchers said.

"We've long hypothesized about oceans on Titan and now, with multiple instruments, we have a first indication of seas that dwarf the lakes seen previously," Jonathan Lunine, Cassini interdisciplinary scientist at the University of Arizona, said in a written statement.

Although the researchers admit that there is no conclusive evidence that the features are liquid seas, their smooth appearance and shape are among the characteristics that suggest they are composed of a fluid.

The scientists believe the liquids are a mixture of methane and ethane, which are prevalent in Titan's atmosphere.

Titan is the second-largest moon in the solar system and is about one-and-a-half times as big as Earth's moon.
 
The Cassini-Huygens mission is a joint project of NASA, the European Space Agency and the Italian Space Agency.