Ceilidh

Michael Zey
st covering 2.1 billion kilometers to explore one of the greatest enigmas of the Solar System.(NASA/JPL/Space Science Institute

Many of the weather processes found on Earth - rain falling on hills and flowing down channels into riverbeds and around islands - also are happening on Saturn's icy moon Titan, but with different materials, scientists said yesterday.

A week after a European space probe penetrated Titan's haze and landed on its surface, scientists say data show that the moon has a dynamic, eroding surface transformed by liquid methane playing the role that water serves on the Earth.

The methane - natural gas held in liquid form by the intense pressure and minus-290-degree temperatures of Titan's surface - rains from the sky and courses down highlands through channels into lakebeds and broad deltas, they said, similar to processes that take place on Earth.

"We now have the key to understanding what shapes Titan's landscape," Dr. Martin G. Tomasko of the University of Arizona said in Paris to describe the mission's first scientific results. "The physical processes shaping Titan are much the same as those shaping Earth."

Scientists said analyzing data from the Huygens probe that landed on Jan. 14 will keep them busy for years. But an early look at this information, including some 350 pictures, confirms that the moon could be a model for processes that happened on Earth billions of years ago.

"We are really extremely excited about these results," said Dr. Jean-Pierre Lebreton, mission manager for the European Space Agency's Huygens project. Scientists should start dreaming about one day sending a rover spacecraft to Titan to explore its unique terrain, he said.

The probe, carried to Saturn by NASA's Cassini spacecraft, landed on a surface with the consistency of loose sand that scientists said appeared to be moistened by methane rain. Heat generated by the spacecraft warmed the surface material, causing bursts of methane gas to boil up around the craft, scientists said.

Dr. Tomasko said the craft landed in a spot that was dry at the time, but appeared to have been rained on recently. "Does that mean yesterday or the day before, the week before? We don't really know," he said. "But the feeling is, in the place we landed, it must rain fairly frequently."

Since no liquid methane was spotted on the surface, he said, it is also possible that Huygens landed in an area that is relatively arid. "It's more like Arizona or someplace like that, where the riverbeds are dry most of the time," he went on. "But after rain, you might have open flowing liquids and pools. These pools gradually dry out; the liquid sinks down into the surface."

Dr. Tobias C. Owen of the University of Hawaii's Institute for Astronomy, noted that nitrogen was the dominant gas in Titan's upper regions but the concentrations of methane increased sharply near the surface. This indicates that there is a big source of methane at ground level, he said, most likely as a liquid very near the surface or on top that is continually renewing the supply of the gas into the atmosphere.

Scientists said the surface was covered with dark deposits from organic materials making up the haze that shrouds Titan. The material settles out of the atmosphere and when washed from higher elevations by methane rain, concentrates at the bottom of channels and riverbeds.

Instrument scans indicate that some of the surface is hard-water ice that flowing methane carves out into channels. Surface images show small rounded pebbles in a dry riverbed nearby, scientists said, adding that spectral analysis of the pebbles indicated that they were made of dirty water ice that had somehow been worn smooth by erosion.

PHOTO1: This image released NASA (news - web sites)/JPL/Space Science Institute shows Saturn's moon Titan in ultraviolet and infrared wavelengths. The European probe Huygens made its final descent towards the Saturn moon Titan, culminating a seven-year quest covering 2.1 billion kilometers to explore one of the greatest enigmas of the Solar System.(NASA/JPL/Space Science Institute