Probe Lands on Saturn Moon

A European space probe today ended a seven-year, 2bn-mile voyage when it landed on one of Saturn's moons.

It is hoped that scientists will now receive information which will help them unlock the secrets of Titan, a mysterious cloud-covered body. The signal received from the Huygens probe was only a "carrier signal" used to beam transmissions to its mother ship, Cassini. Useful data will only be obtained when a stronger transmission is relayed to earth by Cassini.

Professor Colin Pillinger, head of planetary science at the Open University and the man behind the doomed Beagle 2 mission to explore Mars, said: "We are very, very pleased to know how it's gone so far. We still have to know that the instruments are switched on. We're really sitting on the edge of our seats here."

The probe is thought to have reached the surface at about 11.30am GMT, having parachuted through Titan's thick, smoggy atmosphere. A signal from the craft picked up by Earth-based radio telescopes continued hours after the landing was scheduled to have taken place, indicating that Huygens was safely on the surface.

Scientists believe it touched down on land rather than into a lake or sea of liquid hydrocarbons. But they will not know until later today if the probe's instruments are working properly, when confirmation of the landing is relayed to the European Space Agency (ESA) operations control centre in Darmstadt, Germany. The first black and white images from Titan are due to arrive later tonight.

Dr Simon Green, of the Open University, said: "We're sure now that the probe has landed. What we don't know is what it has landed in and what the instruments are going to tell us.

"The fact that the signal continued long before the nominal end of mission at plus three minutes tells us that the probe did survive."

Engineers are counting on the probe to have at least three minutes in which to transmit information and images from Titan's surface before its battery runs out.

Huygens left Nasa's Cassini mother ship for Titan on Christmas Day. Controllers received a signal before the scheduled landing time earlier today showing it had begun its descent to Titan, the only moon in the solar system thought to have a significant atmosphere. It is one and a half times heavier than Earth's, but scientists believe the two atmospheres share some similarities.

"Its atmosphere is thought to be somewhat like that of the Earth when the Earth was first formed," Alan Smith, the ESA's deputy head of operations, told the Associated Press. "So people could extrapolate from the measurements they make back to the atmosphere of the early Earth.

"I expect it to be a very interesting and scientifically challenging moon to visit. The Huygens' mission is the first one to get there, that's why it's so exciting."

Much is riding on the success of the 9ft wide probe, which cost £250m. Failure would be a devastating blow for its scientists, some of whom have devoted half their working lives to the mission.

One hazard would be landing on a solid slope in a position that failed to permit a strong signal back to Cassini, and from there to Earth. Saturn is so far away that it takes 66 minutes for radio waves travelling at the speed of light to cross space from the planet to Earth.

Britain's leading Huygens scientist, Dr John Zarnecki, from the Open University, said: "This is not like the planet Mars, where we can return every couple of years. Titan is very, very far away. This is going to be our only shot at it for an extremely long time."

The Cassini-Huygens mission, a project undertaken by Nasa, ESA and the Italian space agency, has been the most ambitious unmanned space mission of all time.

Launched in October 1997 from Cape Canaveral, Florida to study Saturn, it reached the planet on July 1 last year. Since then, it has rewarded scientists with a wealth of data, including extraordinary images of the planet's rings.

Huygens - named after Titan's discoverer, the 17th-century Dutch astronomer Christiaan Huygens - piggybacked on Cassini for a journey that followed a complex route, swinging by Venus, Earth and Jupiter to obtain an extra kick from each planet's gravity.

It carries instruments to explore what Titan's atmosphere is made of, and find out whether it has the cold seas of liquid methane and ethane that experts believe exist.

Scientists calculate that, if that were the case, the seas would have waves seven times higher than those on Earth, but they would move more slowly and be further apart.

Temperatures of -180C (-292F) make the prospect of finding Earth-type life extremely unlikely, although one group of US scientists claims conditions on the moon could support specially adapted life forms.

Just in case Huygens is not alone on the moon, a CD containing four pieces of instrumental music composed by French musicians Julien Civange and Louis Haeri is being carried on board.

"The European Space Agency wanted to add artistic content to the mission, to leave some trace of humanity in the unknown, and send a sign to any possible extraterrestrial populations," Mr Civange said.