Secret sea: Swathed in its thick blanket of atmosphere, frigid Titan approaches the brilliant rings of Saturn.

Credit: NASA

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SYDNEY: Saturn's largest moon may have a hidden underground ocean according to new findings from the Cassini-Huygens spacecraft. If liquid water is present on Titan, could simple life exist?

"While other icy satellites have internal water oceans, Titan has abundant organics on its surface too," said Ralph Lorenz a planetary scientist at John Hopkins University, Baltimore, Maryland. "That's a very appealing astrobiological combination."

Wealth of weird features

A team led by Lorenz reported exciting preliminary results from a recent survey of Cassini radar images today in the U.S. journal Science.

Previous observations of Titan have revealed a wealth of weird features, including some that wouldn't look out of place on our own planet: mountain ranges, dunes, lakes and even volcanoes - but on Titan they are made of hydrocarbons, such as methane, and ice as hard as rock.

A moon made of ice and methane - with an average surface temperature of -179°C - doesn't sound like the most hospitable spot for life as we know it, but throw liquid water into the mix, and we're looking at conditions that seem more favourable for the creation of life.

Initial predictions about Saturn's largest moon saw its surface covered by a hydrocarbon ocean. The landing of the European Space Agency's Huygens probe in 2005, followed by radar images from its space-based partner, Cassini, however, dispelled this theory and revealed a largely solid surface. But even with the new influx of data, the internal structure of the moon has been poorly understood.

To find out more, Lorenz and his team have studied Cassini radar images taken between October 2004, when the orbiter first reached Titan, and May 2007. By comparing images of the same fixed geological features, the scientists have discovered that the moon does not rotate exactly as a solid satellite would be expected to.

According to predictions, Titan should rotate about its own orbit in such a way that it always shows the same face to Saturn. However observations showed that the fixed features observed did not remain stationary, but in fact moved by tens of kilometres over the three years studied.

Drifting crusts

This has led researchers to the conclusion that winds in the atmosphere cause the moon's solid surface, or crust, to rotate relative to its inner layers. The crust 'drifts' eastward or westward depending on seasonal variations of wind directions near the surface. This is only possible if a liquid ocean is present beneath the surface.

"This is a fun cross-roads in science," said Lorenz. "The geophysical structure of a planetary body being revealed by the influence of its changing weather patterns on its rotation."

Although other explanations cannot yet be ruled out, an internal body of liquid is in line with several existing theories. If further data confirms the hypothesis, Titan will be the fourth moon in the Solar System to demonstrate a subterranean ocean after Jupiter's moons Europa, Callisto and Ganymede.

In an accompanying commentary also published in Science, Christophe Sotin, professor at NASA's Jet Propulsion Laboratory in Pasadena, California and Gabriel Tobie of the University of Nantes in France, commend the finding and the implications for finding life, noting that "Cassini-Huygens and future missions will help us to understand the cycle of the elements and organic molecules that play a key role in the formation and evolution of life."