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Last Updated: Wednesday, 13 December 2006, 10:34 GMT
Mountain range spotted on Titan
By Jonathan Amos
Science reporter, BBC News, San Francisco

Titan's Sierras are the biggest mountains yet seen on the moon

The Cassini spacecraft has spied the tallest mountains yet seen on Titan, Saturn's major moon.

The range is about 150km long (93 miles), 30km (19 miles) wide and about 1.5km (nearly a mile) high.

The feature was identified by the probe on a recent pass, using a combination of radar and infrared data.

Dr Bob Brown, one of the scientists behind the discovery, said it reminded him of the Sierra Nevada mountains in the western US.

"One could call them Titan's Sierras," the University of Arizona-Tucson researcher added.

The mountains lie south of the equator. Scientists told the American Geophysical Union (AGU) Fall Meeting that the range was probably as hard as rock, but made of icy materials.

The mountains appear to be coated with layers of organic, or carbon-rich, material. This could be methane "snow".

Impact story

Titan is smothered in a thick photochemical haze, so Cassini must use instruments other than its optical camera system to see features such as these mountains.

Dr Brown, who leads Cassini's Visual and Infrared Mapping Spectrometer (Vims) team, said a theory was now emerging to explain how the range formed.

You can think of Titan as the Earth in deep freeze
Dr Rosaly Lopes, Nasa JPL
It was likely they grew as material welled up from below to fill the gaps opened when tectonic plates pulled apart, he explained. This is similar to the way mid-ocean ridges are formed on Earth today.

Dr Brown said the mountains were close to a circular feature which might be an ancient impact basin. He speculated that it was possible a space collision in Titan's past had kicked off the whole process.

"The energy released in the impact was probably large enough for the impactor to punch through the crust of Titan which then caused tectonic disruption in the area, and that these [mountains] occurred some time afterwards.

"If there is anything to this idea, if this is an impact basin, we ought to see something exactly opposite in the geology on the other side of Titan at what we call the antipode; and we haven't seen that yet."

Like Earth

Close to the mountains, Cassini's instruments also detect clouds. It is probable these are forming when the atmosphere is pushed over the elevated region by winds.

The spacecraft's flyby on 25 October has obtained a wealth of new data. As well as the mountains and clouds, the probe saw more detail in the great dune fields that cover the world and spotted what appears to be an icy volcanic flow.

Cassini has been investigating Saturn and its moons since 2004
Scientists are fascinated by Titan because its chemistry may tell them something about the early Earth.

From the few impact craters seen on the surface, scientists know it must be a very active world. There are channels that are probably being carved by liquid methane; it has volcanoes that spew ices; winds are eroding features and depositing material in distant locations.

"You can think of Titan as the Earth in deep freeze," said Dr Rosaly Lopes, Cassini radar team member at the US space agency's Jet Propulsion Laboratory.

"It has a lot of the geological processes that Earth has. In fact, it is more Earth-like than anywhere else in the Solar System. But the surface is very cold; it's about minus 178C."

Becoming clearer

British scientist Professor John Zarnecki was a principal investigator on the Huygens lander which Cassini put on Titan in January 2005.

He said the moon continued to amaze.

"It is incredible to think that all those kilometres away there is a moon which contains so many similar geographical features to those found here on Earth.

"Huygens gave us a panoramic snapshot of the surface of Titan which we continue to anaylse. When coupled with the results from Cassini's flybys of Titan, we are really beginning to build up a detailed picture of the make-up of this intriguing moon."

Cassini-Huygens entered into orbit around Saturn on 1 July 2004. The mission is a co-operative project of Nasa, the European Space Agency (Esa) and the Italian Space Agency (Asi).


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