DARMSTADT, Jan 14: The European probe Huygens made its final descent towards the Saturn moon Titan on Friday, culminating a seven-year quest covering 2.1 billion kilometres to explore one of the greatest enigmas of the Solar System.

The unmanned craft plunged into Titan's roiling atmosphere at the start of a two-and-a-half-hour parachute glide in which it would measure the moon's intriguing weather system and atmospheric gases, scientists said.

Mission controllers - worried that the most ambitious interplanetary mission ever attempted would end disastrously at this hurdle - shouted for joy when Huygens sent a radio signal, picked up by the Green Bank listening station in Virginia.

"The baby is alive," exulted David South wood, director of science at the European Space Agency (ESA). Claudio Solazzo, mission operations chief, said a clam-like shield was designed to protect Huygens from friction heat as it hurtled in from deep space at 20 times the speed of sound and collided with Titan's atmosphere.

"The first thing will be the opening of one small parachute. Soon after that, the main parachute, eight metres wide, will open. After that, all the instruments will be [turned] on. It will be a clockwork process," Mr Solazzo said.

For the next two-and-a-half hours, the 319-kilo craft was scheduled to film Titan's surface, measure wind speed and pressure and analyse atmospheric gases as it descended to the surface.

It would then touch down. But so little is known about Titan that it was unclear as to when and where - the site could be a hard surface of methane ice, or rock, or possibly a chemical sea.

Whatever the circumstances, the instruments are designed to carry on monitoring for another three minutes. Only when data was to be received later, would anyone know whether the huge gamble has been a success, said Huygens scientist Leonid Gurvits.

Titan was chosen because it is the only moon in the solar system that has a substantial atmosphere. Its thick mix of nitrogen and methane is suspected to be undergoing chemical reactions similar to those that unfolded on Earth billions of years ago. That process eventually provided the conditions for life on our planet.

TIME MACHINE: "Titan is a time machine. It will especially provide us with the opportunity to know about the conditions on our early Earth," Alphonso Diaz, NASA Science assistant administrator, told reporters at Huygens mission control, the European Space Operations Centre. -AFP