Out-of-this-world pictures yield the secrets of the orange moon

Images of Titan, the largest of Saturn's 33 moons, have wiped the disappointment of the Mars mission off the face of the Earth. Steve Bloomfield reports

Some of the most astonishing photographs ever to be taken reached Earth yesterday, after travelling nearly a billion miles through space. Taken by a camera which journeyed for more than seven years to reach its target, they are of Titan, Saturn's largest moon, and are already beginning to reveal the secrets of this, one of the most tantalising bodies in the universe.

Some of the most astonishing photographs ever to be taken reached Earth yesterday, after travelling nearly a billion miles through space. Taken by a camera which journeyed for more than seven years to reach its target, they are of Titan, Saturn's largest moon, and are already beginning to reveal the secrets of this, one of the most tantalising bodies in the universe.

The colour images, which were beamed back to the European Space Agency's (ESA) base in Darmstadt, Germany, clearly display Titan's bright orange surface. It is covered by a thin haze of methane and what, at this early stage, scientists believe could be a methane sea with islands and a mist-shrouded coastline. One image appears to show boulders that were probably formed from ice.

Scientists, who have long believed Titan's atmosphere mimics that of Earth in its early days, were ecstatic. Dr Andrew Ball of the Open University, who has worked closely on the project, said: "This is fantastic, it's given us a real boost. We had extracted all the information from previous missions and waited years to gain this sort of data. We have opened a window on this alien world."

The little hero that brought back these images to Earth is the 9ft-wide Huygens probe, the world's most ambitious unmanned mission. A collaboration between Nasa and the ESA, it has cost more than £2bn and has taken some 25 years to plan.

British scientists involved in the mission said they were astounded by the quality of data they had received after Friday's successful descent to Titan. Professor John Zarnecki of the Open University said: "We have science data from all of the nine sensors on the Surface Science Package and everyone is busy analysing to see what we can tell about the properties of Titan from this. Although a first glance will give us an initial indication we have years of data analyses ahead - this has exceeded all our dreams."

What has got the experts so excited is that they can at last start to unravel some of Titan's secrets. Aerial photographs of the largest of Saturn's 33 moons, taken on the tiny probe's descent, show dark lines that suggest stream beds carved by liquid flowing into a dark area thought to be a sea of liquid methane.

The head of the probe's camera team, Marty Tomasko, a scientist from the University of Arizona, said: "It is almost impossible to resist speculating that the flat dark material is some kind of drainage channel, that we are seeing some kind of a shoreline. Maybe this suggests it was wet not so long ago and hasn't penetrated so far into the surface."

The pictures were transmitted from the space probe - named after Christiaan Huygens, the 17th-century astronomer credited with discovering Titan - back to its mother spacecraft, Cassini, which relayed them to Earth. Sound was also transmitted; the onboard microphone picked up whooshing sounds which scientists believe were likely to be the wind whistling past the probe on its descent. Titan's winds can reach 1,000 mph, and there is hope that the sound of lightning strikes may also be picked up. A potential holiday destination it is not.

Titan is the first moon other than the Earth's to be explored, and is the only one in the solar system known to have a significant atmosphere. This is rich in nitrogen and contains about 6 per cent methane, making it one and a half times thicker than Earth's. Very little is known about Titan - a moon that is even bigger than Mercury and Pluto. The moon is surrounded by an orange haze caused by frozen particles floating in the atmosphere.

So has ended successfully a mission that was launched from Cape Canaveral, Florida, on 15 October 1997. In order to gain the gravitational pull it required to get as far as Titan, the spacecraft made two "gravity-assisted swing-bys" around Venus and one each around Earth and Jupiter.

It arrived at Saturn in July 2004 and continued orbiting the solar system's second largest planet until Christmas Day, when Cassini released the Huygens probe. The probe's descent to Titan was slowed by three parachutes, while a protective heat shield ensured a safe passage through the dense atmosphere. Its successful landing on Friday led to scenes of jubilation among scientists.

The sixth rock from the Sun

* Saturn is the second largest planet and nearly 900 million miles from Earth. An average day lasts 10 hours 32 minutes, and the planet takes 29.5 Earth years to complete one orbit

* Saturn's climate is not good. Winds on the surface can reach 1,000mph and temperatures can fall as low as 270 degrees below freezing point

* Saturn has a small footnote in rock history. David Bowie's 'Space Oddity' and Elton John's 'Rocket Man' have their sources in Ray Bradbury's short story 'The Rocket Man', whose hero makes three-month treks to the planets, including Saturn

* The pressure on the surface of the planet is about the same as it would be two miles below the sea on Earth. At this depth, the pressure would crush a human body

* Hollywood's Academy of Science Fiction, Fantasy and Horror films gives the Saturn Awards for the year's movies. Last year's was won, appropriately enough, by the third in the 'Lord of the Rings' series

* Galileo called Saturn 'the planet with ears', but 50 years later, in 1655, Christiaan Huygens determined that the 'ears' were in fact rings, and discovered Titan

* Saturn was the Roman god of sowing and reaping, and Saturnalia the riotous midwinter festival marking the solstice and the triumph of the Sun as the days again grew longer

* Titan is the largest moon of Saturn and the second largest in the solar system. It is also larger than the planets Mercury and Pluto