From 750m miles away, a glimpse of a frozen, ancient Earth

Triumphant climax to 20-year project as European probe breaks through to Saturn's moon Titan, revealing rocks, rivers and perhaps a sea

Scientists last night unveiled an aerial study of an alien world, across a distance of more than 750 million miles. From an altitude of 10 miles, a little European robot equipped with camera and microphone took the first picture of the surface of Saturn's moon Titan.

Below the thick methane haze, the descending intruder saw evidence of a shoreline - and perhaps a sea or an ocean - and the telltale pattern of drainage. Close-up pictures from the surface of Titan revealed an enigmatic landscape of eroded boulders.

It was the climax of more than 20 years of planning, and a 2bn-mile voyage lasting seven years. The pictures took 67 minutes to return.

The little space probe called Huygens began falling through the orange skies of Titan just after 9am GMT yesterday. Within 12 hours, jubilant scientists back on Earth had begun poring over the raw images, smudged by transmission artefacts and flawed by data gaps, and marvelling at the contours of an undreamed-of world where the air, seas and high ground may all be composed of frozen methane and ethane, chilled solid or flowing in tides of frozen slush.

"We suspected there would be liquid on the surface of Titan," said Marty Tomasko of the University of Arizona, Tucson. "We suspected we would see things that looked like drainage channels and shorelines, but never that we would be able to see them with this clarity."

John Zarnecki of the Open University said: "If it's not a sea it's a lake of tar, or something liquidish.

"And did one see, perhaps, some waves? Our dreams have been fulfilled. There is activity, there is processing going on, on the surface."

These were just the first of around 350 images snapped as the little flying saucer Huygens descended into a landscape dominated by frozen hydrocarbons and an ambient temperature of -180C (-292F).

It was Europe's first landing on another celestial body. It was a first visit to a frozen version of the primitive Earth. And it was a triumph of cooperation that took the US space agency Nasa, the European space agency and the Italian space agency into orbit around Saturn last July and then on a death dive into one of the most mysterious moons in the solar system.

"Titan takes us back to the conditions that probably existed in our early Earth. All the ingredients are there for life except one: oxygen," said David Southwood, the director of science at the European Space Agency, who began work on the mission in 1982.

"The atmosphere of Titan is a cooking pot already. There is weather on Titan. We want to know if there's lightning on Titan, not just out of curiosity about whether these things occur elsewhere, but because long ago that is how our Earth was; that's how things got started. Maybe it all led to this point, where we go back to look at the beginning."

The mission was launched to answer 20-year-old questions with 10-year-old technology. Cassini, the biggest interplanetary spacecraft ever launched, carried its silent partner Huygens for seven years, looping Venus, the Earth and Jupiter, to arrive at Saturn in July. Cassini went twice round Titan to make sure of its target before it pushed the probe slowly away towards the mysterious moon on Christmas Day.

Titan is bigger than Pluto and Mercury. It is the only moon in the solar system with a dense atmosphere, mostly of nitrogen, but veiled by clouds of hydrocarbons so thick that even as the probe burst through the dark shroud, mission scientists had no idea what they might see.

Everything about the mission was a cliffhanger. Huygens, dormant for almost the whole journey, came to life just before it slammed into the moon's high clouds at nearly four miles a second yesterday. The friction took the probe's heatshield to 8,000C. High above the moon's surface, the first of three parachutes opened, the heat shield blew off, and the saucer-shaped box of six instruments began a slow descent through the Titan's clouds.

Sensors began sniffing the air for the chemical signatures of complex gases; and a tiny microphone began to listen for electrical storms and high winds that might buffet the probe. A camera began snapping up to 750 photographs of the unfolding alien panorama below. And the probe's feeble batteries began to transmit data to the mothership Cassini, by now nearly 40,000 miles away with its receiver turned towards its robot companion.

At the speed of light, signals from Cassini to Earth took 67 minutes to cross the void. The scientists at mission control in Darmstadt, Germany, had no idea whether their baby had survived its first contact with Titan's atmosphere until a giant radiotelescope in the US picked up a tiny bleep from Huygens beginning its descent.

Researchers would have been delighted with just two hours of data, as the probe descended to the Titanian surface.

But the bleep continued for five hours, evidence that the feeble batteries of Huygens had continued to provide power after touchdown, and continued long after the mothership Cassini had disappeared over the horizon, leaving its baby to die alone in the alien landscape, 750 million miles from home.

Cassini sends back its signal

· Huygens is 2.7 metres (over 8ft) across and weighs 350 kg (55 stone)

· Cassini is the largest interplanetary spacecraft ever built: the size and weight of a 30-seat passenger bus. Launched in October 1997 it spent four years making 70 orbits of Saturn and its moons

· It is two storeys tall and 3.9 metres wide

· It takes 20 watts to send a radio signal from Saturn to Earth. It takes the same power to run a refrigerator's interior light

· Cassini's 1999 flyby of Earth slowed the planet's orbit and delayed the millennium by a hundred trillionth of a second

· Cassini travelled 2bn miles or 3.2bn kms to reach Saturn. This is like a bee flying from London to Hawaii and back

· The Deep Space network antennae detected a signal from Cassini with a power of 0.0000000000000001 watts, 67 minutes after Cassini's 20-watt transmitter sent it

· 4,300 people were involved in designing, building and managing the mission. British scientists were involved in six of Cassini's 12 instruments and two of Huygens's six instruments