Oct. 28, 2004
BBC
Photo: The pictures are the closest ever taken of the moon
Scientists examining pictures from the Cassini spacecraft think they may be closer to showing there is liquid hydrocarbon on Saturn's moon Titan.
Radar images taken of a strip of the moon revealed dark patches, which could indicate liquid methane or ethane.
This is important because scientists have theorised that the satellite may harbour hydrocarbon oceans and lakes.
The images also suggest that the surface of Titan could be shaped by strong winds.
"Titan is an extremely dynamic and active place, not only in its atmosphere but on its surface as well," said Jonathan Lunine, Cassini imaging scientist.
"We have seen evidence of atmospheric activity, possibly winds, moving material around."
The scientists stress that before any firm theories can be established they have to compare the latest data with other findings from an instrument called the Visual Infrared Mapping Spectrometer (Vims).
Mystery also surrounds the composition of a cloud formation near Titan's south pole. Scientists expected it to be made of methane. But the particles appear to be too big to be methane.
Small strip
The Cassini scientists used radar to gain an idea of the topography of Titan over a strip measuring 100km by 2,000km.
"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."
The daughter of one of the scientists said one dark patch looked like a black Halloween cat, so the team have 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 mysterious planet's surface.
At the moment the scientists are not sure what has caused them. Similar streaks observed on Mars were made by dust against big obstacles.
The Cassini scientists think that the streaks on Titan might be caused by the movement of various materials, like 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.
The first images were the clearest yet of the moon's surface, and scientists said they expected better images later.
Attempts to view Titan's icy surface are difficult because of the thick, orange haze that envelops the moon. But scientists had hoped Tuesday's pass would be close enough for Cassini's instruments to penetrate the satellite's dense smog.
Whole new world
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
http://news.bbc.co.uk/2/hi/science/nature/3963321.stm