Two million miles to go ... on course for a Red Christmas as the Beagle goes solo

After six months and 17 days it was the final 30 seconds of the 250 million-mile journey that proved to be the most tense for the scientists involved in the mission to Mars.

This was how long Mike McKay, the director of flight operations, paused before announcing to the world the Beagle-2 space probe had successfully disengaged from its mother ship, the Mars Express.

It marked a critical moment in the history of British space exploration, as the world's most ambitious attempt to search for signs of Martian life passed a crucial test of its technology. "We can confirm that we have Beagle-2 separated successfully," Dr McKay said yesterday at precisely 11.12am as he heard confirmation over his headset from engineers at the European Space Operations Control Centre in Darmstadt, Germany.

It was left to Professor David Southwood, the European Space Agency's director of science, to explain the importance of the moment. "Beagle has separated from us and it's on its way to Mars. It's been a very intense morning. The team deserves many congratulations," Professor Southwood said. "This is just the beginning. We've now got to wait until Christmas Day to make the next steps [but] the mother and baby are both doing well."

If the critical "spin-up and eject" mechanism had failed it would have meant that Beagle-2 would still be locked in a deadly embrace with its mother ship, in effect ending the £100m mission in embarrassing failure. Now that it has been freed, Beagle-2 can continue its direct journey to the surface of Mars where it will be the first space probe since the Viking mission of the 1970s to land and search for the chemical signature of extraterrestrial life.

It is scheduled to parachute into the Martian atmosphere in the early hours of Christmas morning - landing in Isidis Planitia, a large basin north of the equator - while the Mars Express mother ship will continue its separate journey taking measurements from its orbit around the Red Planet. A nervous team of engineers who made the spring-loaded device that gently pushed and spun Beagle-2 away from Mars Express - stabilising it like a spinning rugby ball - beamed with relief when Dr McKay confirmed the separation.

Other scientists at the Royal Geographical Society in London - which had a live video link with the Darmstadt operations centre - punched the air and cheered wildly on hearing the news. But the happiest face of all belonged to Professor Colin Pillinger, a planetary scientist at the Open University, who originally conceived the idea of a lander to probe the Martian dust for the chemicals which would indicate the presence of fossilised life.

Like a master of ceremonies in a bright orange shirt and black jacket, Professor Pillinger expertly fielded questions from the audience during the nervous half-hour between receiving the first preliminary signals of Beagle-2's separation and final confirmation. What happens if you find life, he was asked. "I won't have any difficulty in getting money for the next mission," he quipped. How do you define life? The same way Charles Darwin would have defined life, he answered. "It must be capable of reproducing itself and evolving."

When confirmation finally came through, Professor Pillinger likened it to a football match played in two legs. "And both of them were away, a long way away in space. We've travelled 250 million miles, we've got a one-nil result in the first leg: we're playing the second leg on Christmas morning," he said.

Before Beagle-2's array of robotic instruments can get to work, the 154lb (70kg) probe must first land softly. Its heat shield must protect against burning up in the Martian atmosphere, its parachute must open, its three gas-filled bags must inflate and its solar panels have got to peel back and soak up the sun's rays.

Beagle-2 - named after the ship that sent Darwin on his own voyage of discovery - will enter the Martian atmosphere at 12,500mph and must in the space of just seven crucial minutes slow down quickly enough to land gently on Mars.

If all goes to plan, at about 5.15am on Christmas morning, Beagle-2 should be able to send its first signal and picture to the American Mars Odyssey probe orbiting overhead. When the Martian lander's relayed message eventually reaches Earth, it will mean just one thing: the beagle has landed.

The astronomer Sir Patrick Moore described Beagle-2 as a "British triumph". He predicted that any life on Mars would be low level and probably aquatic. "I'm very hopeful that it will succeed because this is important to see if there is life on Mars, and I do not mean Martians or aliens. I'm 50-50 if it is there but if it is, then Beagle will find it."

Professor Pillinger stressed that there was no question of winning a race with the US space agency Nasa - which has two probes due to touch down early in January.