The finding propels Titan into a short list of places including Jupiter's moon Europa and Saturn's smaller moon Enceladus suspected of harboring underground seas.

"The evidence is strong that Titan is squishy," said planetary scientist Jonathan Lunine, with Cornell University.

The evidence was put together during six passes over Titan by Cassini, which is orbiting Saturn, between 2004 and 2011. During the flybys, scientists measured minute changes in the pitch of radio signals passing between the spacecraft and Earth to figure how much Saturn's gravity deformed the moon.

They then turned to computer models to match a 10-meter (33-foot) distortion with possible scenarios to explain what was going on. The more solid the moon's interior, the less it would be impacted by Saturn's gravity.

"The measurement is pretty conclusive about the existence of an internal ocean," said lead researcher Luciano Iess, with Sapienza University in Rome, Italy.

"The presence of water does not imply life," he added. "“But Titan has many interesting ingredients - hydrocarbons, a hydrological cycle and a thick atmosphere."

Scientists have no idea if the ocean is in contact with rock, a possible source of minerals and other components believed to be needed for life.

Based on the Cassini findings, Titan's suspected ocean lies about 100 kilometers (62 miles) beneath the surface.

Although the moon sports lakes of liquid hydrocarbons, such as methane and ethane, Titan's ocean is probably mostly water.

"The subsurface ocean has to be made of water, or water mixed with a relatively small percentage of salts," Iess said.

If the ocean were liquid hydrocarbons, the heavier surface ice would sink and Cassini would see a global hydrocarbon ocean on the surface, he added.

Scientists hope to refine gravity maps of Titan after additional Cassini flybys planned through 2017.

Cassini arrived at Saturn in 2004.

The research appears in this week's issue of Science.

(Editing by Todd Eastham)

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