(Sen) - Saturn's largest moon Titan has already excited planetary scientists with the discovery that it is the most Earth-like body in the Solar System. Now it seems clear that it hides an ocean of water beneath its surface.
NASA's Cassini space probe orbiting Saturn has detected powerful tides affecting Titan which point to there being a vast underground sea.
Titan is unique among moons in the Solar System because it has a dense atmosphere. That allows rains to fall and the surface shows similar features to Earth's such as lakes, river deltas and shorelines.
Those surface features differ from ours because they were produced by liquid methane rather than water. But the underground ocean is believed to be filled with water.
Its presence also causes the crust of Titan to distort by several metres, the Cassini probe found during observations carried out between 2006 and 2011. This tidal pull, as Titan orbits Saturn in an elliptical shape every 16 days, stretches the moon into a rugby-ball shape when it is closest to the planet.
Luciano Iess of the Università La Sapienza in Rome, lead author of a paper published in Science magazine, said: "The important implication of the large tides is that there is a highly deformable layer inside Titan, very likely water, able to distort Titan's surface by more than 10 metres."
He added: "We know from other Cassini instruments that the surface of Titan is made of water ice mostly covered with a layer of organic molecules – the water ocean may also be doped with other ingredients, including ammonia or ammonium sulphate.
"Although our measurements do not tell anything about the depth of the ocean, models suggest that it may be up to 250 km deep beneath an ice shell some 50 km thick."
The UK's leading Titan expert is Professor John Zarnecki, Professor of Space Science at the Open University. He was part of the team that successfully landed the space probe Huygens on Titan in 2005.
The layers of Titan, including an undergound ocean, discovered by Cassini. Credit: ESA/Angelo Tavani
Professor Zarnecki told Sen: "Titan continues to amaze us! Before Cassini-Huygens arrived in 2004, I used to worry that we were over-hyping it and that when we arrived, we would find a dull and boring ball of ice with not much going on.
"But the reality is a million miles from this. We now know that the atmosphere, the surface and now the sub-surface are all fascinating environments in their own rights.
"There was previously a hint that something interesting was going on below the surface - but this paper dramatically proves this to be the case. We just have to go back to Titan as soon as possible!"