Ninety minutes after liftoff from the Russian space base in Baikonur, Kazakhstan, the orbiter -- carrying the "Beagle 2" lander -- separated from an unmanned Soyuz rocket and began its 400 million kilometer (250 million mile) trip to uncover the mystery of life on Mars.

If all goes according to plan, on Christmas Day the Beagle-2, named after the ship that took Charles Darwin on a quest for the origins of life, will land on the planet and begin its exploration.

A few hours before launch time at 11:45 pm (1745 GMT), ESA scientific director David Southwood voiced his appreciation of Europe's cooperation with Russia in the 190-million-dollar (162 million euro) Mars mission.

"I'm really happy at this launch, also happy with the Russian involvement: this would have been unthinkable 20 years ago," he said.

For Europe it was "our first step" towards exploring other planets, Southwood noted.

The orbiter is to reach Mars in less than seven months, its seven cameras, radars and spectrometers ready to scour the planet's surface from orbit.

Once in orbit around the Red Planet, the Mars Express will launch the Beagle-2, which will descend to the equatorial region of the Isidis Basin to test the Martian soil, probably landing in the small hours of December 25.

Scientists hope that its lander's findings could, like the data Darwin brought back from the remote Galapagos islands, revolutionise man's understanding of his place in the universe by detecting signs of life on Mars, a notion that has fired men's imagination for centuries.

The Beagle-2, seen in simulated images bouncing on the Martian surface like a large football, contains a package of sophisticated instruments, a pair of stereoscopic cameras, a solar power pack and a "mole" robot that can inch along the Martian surface, or drill a metre or more below it, to sample the soil.

The Mars Express will be followed by two vastly better-funded US missions, one scheduled for June 8 and the other provisionally due to lift off on June 25, also aiming to settle once and for all the question of whether life exists, or has ever existed on Mars.

They will be joined by a Japanese mission launched in 1998, the Nozomi, which after getting lost due to technical mishaps is due to arrive next year.

All four missions are taking advantage of the fact that in August Earth and Mars will be in opposition -- at their closest points.

For the moment however, the Beagle-2 is hogging the limelight, its profile raised by the presence on board of a spot painting by the British artist Damien Hirst -- to serve as a colour calibration chart for its cameras -- and a call-sign composed by the British pop group Blur.

First results from the mission are expected "early next year," Southwood said.

The ESA official regretted that European countries had not been more deeply involved in space exploration.

"So far the French have been the only people in western Europe who feel that a developed nation should have a space project. We have to do things in space, to look outwards," he said.

By pressing ahead with the Mars Express, the ESA is taking a gamble that small, quick, cheap missions can contribute usefully to space research.

The strategy has its critics who say that it can cut too many corners in design and testing compared with bigger, lavishly-funded long-term projects.

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SPACE.WIRE