A Titanic leap

After a seven-year voyage covering two billion miles, Cassini-Huygens mission reaches Saturn's moon

It took seven years for the Cassini-Huygens spacecraft to travel the two billion miles to Saturn and its moon Titan but it was the final 12 hours that proved the most heart-stopping.

It took seven years for the Cassini-Huygens spacecraft to travel the two billion miles to Saturn and its moon Titan but it was the final 12 hours that proved the most heart-stopping.

Scientists were jubilant last night as they witnessed a successful end to the most ambitious unmanned mission undertaken in space. In emotional scenes from mission control in Darmstadt, Germany, they confirmed yesterday the tiny probe had landed safely on the frozen surface of Titan.

It was the furthest soft landing in the history of space exploration and ­ this time at least ­ the heat shield worked, the three parachutes opened as planned and the radio transmitters sent back the all-important signals suggesting all had gone according to plan.

The landing provided a dramatic conclusion to the Cassini-Huygens mission, which was 25 years in the planning and had cost about £2bn, split between America's National Aeronautics and Space Administration (Nasa), the European Space Agency (ESA) and the Italian space agency.

The first pictures of the surface of Titan came through last night. One showed a system of channels that had probably been cut into the surface by liquid. Another taken closer to the surface revealed what appears to be a terrain of boulders. Scientists said the images were taken from a height of about 10 miles (16km) and the channels must be the size of large rivers.

Professor John Zarnecki said data from Huygens has flowed into mission control and has covered a total period so far of three hours seven minutes and 26 seconds from the point when the Huygens probe first began to parachute down to Titan to the time when the transmissions stopped. About one hour and 10 minutes of the data was collected as the probe sat on the surface of Titan.

Professor Zarnecki said the probe landed on a surface that appears to have the consistency of soft-to-medium compacted snow. "We're not sitting on a liquid, we're sitting on a solid but how solid we don't know," he said.

The success has been fêted by all concerned. "The morning was good, the afternoon was better," announced Jean-Jacques Dourdain, director general of ESA. "We are the first visitors of Titan. We shall unveil the secrets of this new world," Professor Dourdain said. "A very complex machine has worked beautifully. It is a fantastic success for international co-operation."

Packed with instruments, the Huygens probe is designed to describe the chemical and physical nature of the atmosphere of Titan ­ the only moon in the solar system that has one ­ as well as to analyse its mysterious surface, about which next to nothing it known, except that it is minus 180C.

The heat-shield and three parachutes on Huygens were designed to slow the probe from 11,200mph outside the atmosphere to 12mph as it landed.

Radio transmitters on board Huygens relayed data as it floated through the Titan's clouds of noxious organic gases ­ back to the Cassini spaceship orbiting Saturn. Its cameras are designed to take 1,100 images as the probe made its descent.

Professor David Southwood, ESA's science director, said the stream of data sent from Huygens as it made its two-hour journey through Titan's atmosphere, and the time it spent transmitting from its surface, would prove invaluable.

"We're going to be working hard over the next hours and days but this data is for posterity. It is an historic event," Professor Southwood said.

Even by the extraordinary mysteries of space, Titan is a weird place. Scientists know little about the second biggest moon in the solar system ­ a moon that is even bigger than the planet Mercury ­ except that it is obscured by an orange glow caused by frozen particles floating in its upper atmosphere.

A crucial issue was whether the probe would land in a liquid ocean of hydrocarbons or solid ground. First indications suggest it landed on terra firma.

Like on Earth, Titan's atmosphere is largely composed of nitrogen, but Titan's atmosphere also contains organic gasses that would, on Earth, be indicative of life ­ an unlikely proposition on Saturn's moon because of the frozen temperatures.

Simon Green, a planetary scientist at the Open University, said the chemical analysis of Titan will help scientists studying the origins of life on Earth some 4 billion years ago.

"It's like looking at the Earth's primitive atmosphere. It's a great laboratory for studying the past history of life on Earth," Dr Green said.