Scientists examining images from the Cassini craft think they may be closer to showing there is liquid hydrocarbon on Saturn's moon Titan.

Radar images of a strip of the moon, covering 1% of the surface, revealed dark patches which could indicate liquid methane or ethane.

The images also show streaky areas of the surface could be caused by winds.

They need to compare the images with more readings, but they said the moon was certainly "geologically alive".

Scientists had theorised that the satellite may harbour hydrocarbon oceans and lakes.

"On early Earth, there was organic material and something happened to those molecules that gave rise to life," said Jonathan Lunine, Cassini imaging scientist.

"We had to find a place elsewhere in the system where that process is being replicated." He added: "It seems to be happening on Titan."

Mystery book

The scientists stressed that before any firm theories could be established they had to compare the latest data, which gives the clearest and closest view of the moon yet, with other findings from an instrument called the Visual Infrared Mapping Spectrometer (Vims).

"The radar instrument is a lot like shouting and listening for the echoes," said Charles Elachi, director of the US space agency's Jet Propulsion Laboratory in Pasadena, California. "In a way we have been listening to Titan's whispers - hearing Titan in its own words."

What the radar data showed was a series of light and dark patches. The dark patches represent areas that reflect fewer radio waves sent out by the radar. Because liquid is known to absorb radio signals, the scientists think they might be looking at giant oily lakes.

CASSINI'S KEY PARTS

1. Antennas enabling communication with Earth2. Boom carrying instrument to measure magnetic fields3. Two cameras will take 300,000 pictures of the planet4. Infra-red spectrometer analyses Saturn's temperature and composition5. Radioisotope thermoelectric generators supply 750W of power6. Cassini has two engines - one is a back-up7. Thrusters used for small changes of direction or speed8. Huygens probe will land on Saturn's largest moon, Titan9. Plasma spectrometer measures charged particles and solar winds

The daughter of one of the scientists said one dark patch looked like a black Halloween cat, so the team has named the feature "Si-Si's Cat" after the young girl.

The data sent back from the Cassini spacecraft during its flyby of Titan also revealed a series of streaks on the satellite's surface.

At the moment, the scientists are not sure what has caused them. Similar streaks observed on Mars were made by dust against large obstacles.

The Cassini scientists think that the streaks on Titan might be caused by the movement of various materials, such as liquid or even ice.

"What is great is that we have something we can map and monitor over time," said image scientist Alfred McEwen. "How these patterns change can give us information about the surface topography of Titan."

However, there is still much uncertainty over what Cassini's pass has revealed about the moon.

"In my mind, unveiling Titan is like reading a mystery book," said Dr Elachi. "We will need to look at all the images over many flybys to put the puzzle together."

Piggy back

Later this year, the piggybacked Huygens probe will be released from Cassini and enter Titan's atmosphere.

It will transmit data during its parachute-assisted descent, and carry out science tasks on the surface - if it survives.

Streaking of surface materials can be seen in the equatorial region of Titan

Conditions on Titan - which is the second biggest moon in the Solar System - are thought to be very similar to those on Earth 4.6 billion years ago. Temperatures rarely venture above -179C (-290F) and the atmosphere is dominated by nitrogen and carbon-based compounds.

So mission scientists think the moon might have something to teach us about the conditions that were necessary for the origin of life on our planet.

Cassini's flyby - one of 45 planned for its tour of Saturn - is expected to give a taster of what Huygens can expect when it enters Titan's atmosphere.

Cassini entered into orbit around Saturn in July, on its four-year mission to explore the ringed planet and its moons. It is a cooperative project between Nasa, the European Space Agency (Esa) and the Italian Space Agency