There are only a few desperate options left for contacting the little lander after a month of failed attempts by the European orbiter Mars Express, NASA's Mars Odyssey and the giant Lovell telescope in central England.

"We haven't found Beagle 2, despite three days of intensive searching," said Colin Pillinger, the professor largely responsible for the first British-built spacecraft ever to be sent to another planet.

"Under those circumstances, we have to begin to accept that if Beagle 2 is on the Martian surface, it is not active," Pillinger told a press conference in London.

Mars Express tried unsuccessfully over the weekend to make contact with the pint-sized probe, following a 10-day period of radio silence that was designed to force Beagle 2 to switch into emergency transmitting mode.

"There is one more thing that we can do... It is very much a last resort," Pillinger said.

"We will be asking the American Odyssey spacecraft (team) tomorrow whether they will send an embedded command -- a hail to Beagle with a command inside it," he said.

This "drastic step", effectively telling Beagle to switch off and reload its software, will be repeated in early February by the Mars Express, which is operated by the European Space Agency (ESA), Pillinger said.

Beagle 2 separated as planned from the Mars Express on December 19 but it failed to make contact with Earth after its planned touchdown six days later.

Scientists feared the craft -- designed to unfold like a pocket watch upon landing -- may have been destroyed, failed to open properly or else landed inside a crater, making communication impossible.

"It's not time to grieve. We must look to the future," Pillinger said, indicating that other British missions to Mars were in the pipeline.

The feared loss of Beagle 2 contrasted with the successful landing of the NASA spacecraft Spirit which started beaming back high-resolution photographs of the red planet within hours of touchdown.

Spirit stopped beaming data last Wednesday, possibly because of a computer glitch, although it did acknowledge on Thursday that it had received a transmission from Earth.

Mars Express meanwhile scored a coup last week when it detected evidence of ice at the south pole of Mars, a finding which the ESA said confirmed indications by NASA nearly two years ago. The high-resolution pictures gave forceful backing to theories that the Red Planet was once awash with water, one of the precious ingredients for life.

Beagle 2's mission manager Mark Sims on Monday wished NASA the best of luck in locating Spirit and congratulated them on landing on Sunday a second craft, Opportunity, apparently in a small Martian crater.

The Opportunity has since beamed back to Earth sensational pictures of the mysterious landscape at Meridiani Planum, which is near the Martian equator.

Sims thanked NASA and ESA for their help in the search for Beagle 2.

The usually ebullient Pillinger, whose infectious enthusiasm for his brainchild helped to make Beagle a Christmas headline around the world, was considerably more downbeat on Monday than in the past.

"It's back to the bottom of the hill and pushing the boulder back up again," said the scientist, who dressed in black for the press conference. "We hope we will be back and we will continue the search."

SPACE.WIRE