Scientists jubilant as probe lands on Titan

One of the first raw images from the European Space Agency's Huygens probe as it descended to Saturn's moon Titan. Picture / Reuters

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 last 12 hours that proved to be the most heart-stopping.

Scientists were jubilant last night as they witnessed a successful end to the most ambitious unmanned mission ever undertaken in space. In emotional scenes from mission control in Darmstadt, Germany, they confirmed yesterday that a 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 that 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 US$3 billion, split between America's Nasa, Europe's ESA and the Italian space agency.

It was launched in October 1997 and the Huygens probe - which is about the size of a domestic washing machine - was jettisoned on Christmas Day from its seven-year embrace with the much larger Cassini mother ship to begin its journey towards Titan.

Radio astronomers detected the first tentative signals from Huygens at about 10.35GMT but it was not until noon that further confirmation came through.

They had calculated that the probe had landed at about 11.25am - two hours after it had begun its precarious descent through the thick Titan atmosphere.

But it took until after 3.00pm for the first "housekeeping data" to be received from Huygens and for confirmation to be passed on to a waiting world.

"The morning was good, the afternoon was better," announced Jean-Jacques Dourdain, director general of the European Space Agency (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 cooperation."

Packed with six instruments, the Huygens probe is designed to describe the chemical and physical nature of the complex 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 minus180C.

The heat shield and three parachutes on Huygens were designed to break the speed of the probe from 1,522mph to just five metres per second - about the speed at which you fall when jumping off a chair. To everyone's relief, everything appeared to work as planned.

Radio transmitters on board Huygens relayed data as it floated through Titan's clouds of noxious organic gases 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 that the stream of data sent from Huygens as it made its two-hour journey through Titan's dense atmosphere, and the time it spent transmitting from its surface, would prove invaluable.

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

Even by the extraordinary mysteries of the space, Titan is a weird place. Planetary 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 that it landed on terra firma.

Another aspect of Titan is the chemical nature of its atmosphere, which like that on Earth is largely composed of nitrogen. However, Titan's also contains organic gases that would on Earth be indicative of life - an unlikely proposition on Saturn's moon because of the extremely low temperatures.

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

"We're sure it has landed, but we are not sure what it has landed on, or whether the instruments have worked," he added.

Professor John Zarnecki of the Open University, and principal investigator on the Huygens probe, said that it was an emotional moment when the first signals came through from Huygens - which take more than an hour to reach Earth.

"It's very difficult to say anything that doesn't sound cliched. The last 24 hours have been the hardest of the whole project," he said. "There was tremendous relief to put it mildly."

- THE INDEPENDENT