BRITISH scientists were forced to revise their plans to track down the missing Beagle 2 yesterday - just as America celebrated the NASA probe's successful landing on Mars.

Both Britain and the US launched separate missions to try and uncover signs of life on the Red Planet.

Nasa's Spirit Rover probe landed in a crater just south of the planet's equator at around 4.35 am UK time and has already beamed pictures back to Earth.

In contrast to the triumphant US mission, nothing has been heard from the British-built Beagle 2 since its scheduled landing on Mars on Christmas Day.

It successfully separated from the European Space Agency's Mars Express Orbiter on December 19, but attempts to track the probe using powerful radio telescopes have failed.

Yesterday scientists admitted Mars Express - the best way of making contact with the probe - was in the wrong place.

Last week mission controllers redirected Mars Express closer to the planet's poles, to push it into a lower orbit where it will be able to listen for the missing Beagle 2.

But they were forced to devise a new communications strategy because it is not in the orbit they originally expected it to be.

Professor Colin Pillinger, Beagle 2's lead scientist, congratulated the successful NASA mission.

"It goes without saying that we congratulate them and wish them every luck," he said. "That isn't to say we have given up on Beagle 2."

Speaking at a press conference in central London, Prof Pillinger said he hoped to establish contact with Beagle 2 on Wednesday.

He said there would be "a real pull-out attempt on January 7 to get in touch with our spacecraft".

He added: "This is the best chance we have. If our best chance doesn't work we really have to start believing that time is running out."

Dr Mark Sims, Beagle 2's mission manager, said: "Only if we don't pick anything up in auto transmit at that point should we give up."

Nasa's orbiting Mars Odyssey has been searching.

Powerful radio telescopes at the Jodrell Bank observatory in England and Stanford University researchers in California have also failed.