Landing in a crater was among a number of scenarios being looked at by scientists trying to regain contact with the probe, after a sixth opportunity to hear its signal passed on Monday without success.

Others include communication problems, or technical hitches preventing Beagle 2 from making contact with its temporary relay station, the orbiting NASA spacecraft Mars Odyssey.

"We'd have to be incredibly accurate and incredibly unlucky to go right down this crater, which of course would not be good news," said Beagle 2's chief scientist Professor Colin Pillinger.

"There's going to be impact debris around it, which means more rocks," he told reporters in London. "It would certainly make the bouncing process worse. The last thing we wanted was to bounce on slopes or on more rocks."

Seven chances

Seven more chances to hear Beagle 2's electronic bark - a nine-note tune composed by the British pop group Blur - remain until 17 January, including two on Tuesday at 0724 and 2020 GMT and one on New Year's Eve at 0904 GMT.

Lead scientist Prof Colin Pillinger (C)
applauds after Beagle 2's separation

From 6 January there will be four more attempts to be made via Mars Express, the European Space Agency craft on which the 33-kilo probe - named after the Royal Navy exploration ship on which Charles Darwin honed his theory of evolution in the 19th century - travelled to the red planet.

"Our best opportunity to communicate with Beagle 2 is probably to wait until Mars Express is in position," said mission manager Mark Sims.

Jam-packed with revolutionary instruments, the disc-shaped probe had been due to touch down at Isidis Planitia, a large, flat plain near the Martian equator that may once have been awash with water.

Scientists picked the site - a flat, low-lying basin that is 700 square km in area - to minimise natural hazards.
 
But not surprisingly for a pockmarked planet, the area has a crater one kilometer wide at its centre, and possibly hundreds of metres deep.

Craters revealed

It was only revealed by close-up pictures of the site taken by another NASA orbiter, Mars Global Surveyor, minutes after the British probe was supposed to have landed last Thursday.

When Beagle 2 separated from Mars Express on December 19 - after a 400 million km journey through the heavens - it was set to become the first European spacecraft to land on another planet.

During its 180-day mission it was programmed to test rock, soil and air samples for signs of past or present life on Mars.

Although Beagle 2 is one of the most spectacular parts of the Mars Express mission, it represents only about 10% of the overall project's total scientific work, European Space Agency scientists have said.

Other instruments aboard the Mars Express will enable researchers to obtain the most comprehensive coverage of the planet to date.

The equipment include a stereoscopic camera, a means of observing gravity anomalies, a radar capable of seeing beneath the surface and spectrometers to examine minerals and the atmosphere for any evidence of life.