Final 'last resort' to find Beagle 2 before work begins on successor

British scientists have begun planning a Beagle 3 mission to Mars for launch in 2007, even as they try their final "last resort" attempt to contact the missing Beagle 2 lander.

A full review of what may have gone wrong with the craft will be led by Professor Colin Pillinger, the chief scientist on the Beagle 2 mission, at the beginning of February.

But first a message will be sent during the next seven days from the orbiting Mars Odyssey spacecraft telling the Beagle 2 - if it is operational - to reboot its computer. That carries the risk that the machine will never return to life if it was working. But Professor Pillinger admitted that that would be no different from the situation now.

"We have to begin to accept that Beagle 2, if it's on the Mars surface, isn't active," he said yesterday, just over a month after the £35m lander was launched to the surface from the European Space Agency's Mars Express orbiter.

Professor Pillinger was still reluctant to state yesterday that Beagle 2 is dead - but said that to plan its successors, "we need to know which parts of the mission we don't have to study in detail". That means finding out how far Beagle 2 did get, and whether it reached its intended landing spot - an elliptical space about 35km long and 4km wide.

The absence of any signal was finally confirmed yesterday morning following computer analysis at the Jodrell Bank radio telescope in the Midlands of 16 gigabytes of radio data detected by a super-sensitive system tuned to Beagle 2's transmission frequency. It found nothing that could be construed as a signal from the lander.

Professor Pillinger was optimisticthat a Beagle 3 lander could still do pioneering science because it would be able to reuse the experiments that had been built into Beagle 2. Those would search for signs of past life in the planet's soil, "and further, to decide if there's still life on Mars, which would be an even bigger finding," he said. Although the US space agency Nasa now has two landers performing experiments on Mars, neither is equipped to do the chemical experiments that would point to past life on the planet.

However, a lander from Nasa, intended to launch in 2007, may have similar capabilities - giving a new urgency to the replacement mission, and putting a higher priority on working out what went wrong this time.

The Beagle 2 team hopes the orbiting Mars Express, Odyssey and Global Surveyor spacecraft will take pictures of Beagle 2's landing area to see if it arrived on target. The Mars Express cameras are sensitive enough to pick out Beagle 2, which is about 1 metre across - and its parachutes, which measure about 10 metres, should be a much clearer marker.