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Tides of Titan reveal underground ocean

Saturnian ocean Saturn's largest moon Titan may have a huge subsurface ocean according to new data from NASA's Cassini spacecraft.

While scientists have learnt a great deal about Titan atmosphere and surface, very little is known about the Saturnian moon's interior.

The new study, published in the online version of the journal Science, supports the idea of a global ammonia-doped liquid water ocean less than a hundred kilometres below Titan's methane soaked surface.

The teamclosely examined Titan's rotation and orbit to draw conclusions about its interior.

Cassini, which has been exploring the ringed world of Saturn since 2004, has flown past Titan more than 80 times, including six close flybys.

Scientists used subtle changes in radar signals from Cassini during these flybys to develop a gravity map, or geoid, of the moon.

They found that as Titan travels along its 16-day elliptical orbit around Saturn, the geoid changes.

Flexing and stretching

"Saturn's gravity is generating tidal forces, tugging and stretching Titan, just as (to a lesser extent) the Moon raises tides on Earth," says Cassini scientist Dr Sami Asmar from NASA's Jet Propulsion Laboratory in Pasadena, California.

"By monitoring how much Titan is deforming, we can start to draw conclusions about the composition of its interior."

"Titan is flexing rapidly as it orbits Saturn, and that high rate of deformation is consistent with a liquid ocean or more precisely a fluid layer below the surface," says Asmar.

"Examining how this fluid layer is reacting to the gravitational tidal pull of Saturn, tells us about the type of liquid that's likely to be involved in the process."

"The tidal flexing generates heat from friction, which would allow water to exist under Titan's surface in a liquid form," says Asmar.

Professor Trevor Ireland from the Australian National University says "the idea of a subsurface water ocean kept liquid by tidal heating is a reasonable conclusion."

"It could also be an icy mush which would also allow deformation to take place very quickly."

Ireland says we've seen similar processes on the Jovian moons Io and Europa where tidal flexing has heated the interior.

"That's resulted in volcanic activity on Io and what's likely to be a liquid ocean under Europa's frozen surface."