A "tiger team" of engineers has been assembled to investigate why all attempts since Christmas morning have failed to locate the British Beagle 2 lander supposedly sitting on the surface of Mars.

Barreling into the Martian atmosphere at over 12,000 mph while cocooned inside a protective descent module around 0247 GMT December 25, the lander was out of contact with Earth. Minutes later, parachutes and impact-cushioning airbags were to deliver Beagle safely to the surface on an ancient basin near Mars' equator for a 180-day search of past life.

Following the touchdown, Beagle was programmed to contact NASA's Mars Odyssey orbiter when it flew over the landing site. No signal was received by Odyssey, and several further overflights since Thursday morning have ended with the same disappointing result.

The 250-foot radio telescope at the Jodrell Bank Observatory in England has spent hours scanning the sky in hopes of hearing the weak signal from the lander without success.

Now, a special group at the Beagle 2 Lander Operations Control Center in Leicester has been established to devise various ideas to explain the lack of transmissions from the tiny craft.

"We have reconfigured the team at Leicester to divide them into two groups. Group 1 is concentrating entirely on the planning of the commanding and communication sessions you have been hearing about," said Alan Wells from the University of Leicester Space Research Center. "In parallel, we have pulled out a number of specialists into what I'm calling a 'tiger team' or think tank. These are the guys now who are looking at what information we are getting from these passes thus far, looking at the analysis of that data and looking at recovery options that we can pursue."

The tiger team's job is to identify glitches or malfunctions that would cause Beagle's silence and come up with plans to correct them.

"I recognize there are other failure modes that we will not be able to do anything about -- the worst case scenarios," Wells said. "We are not, at the moment, looking at those. We are concentrating our effort on those possible failure modes that we can actually do something about.

"We are having the think tank team look at the data we've got in the areas of communication, the timing and the landing site location."

A possible problem that the group has already attempted to fix is Beagle's onboard clock not telling the correct time. If the clock had been corrupted, the pre-programmed times when the lander was expecting Odyssey and Jodrell contact would be wrong.

On Friday night, "blind commands" were sent from Odyssey to Beagle's landing site instructing the craft to reset its clock. It cannot be confirmed if Beagle received the command but there have been no successful transmissions from the lander in subsequent Odyssey and Jodrell attempts to detect a signal.

"It has reduced the possibility of that as the explanation of why we can't see (a signal from Beagle)," Wells said. "However, it doesn't rule it out. Once we get to pass 14 or 15, we come in with Mars Express. That is a system that has been tested end-to-end with no ambiguity whatsoever and that opens up another opportunity to test these theories of what might or might not have happened.

"We are actually quite restricted with what we can do with Odyssey and even more restricted with what information that we might or might not get with a radio telescope. Mars Express really gives us, I'd say, a ten-fold better means of communication because we tested it before."

Mars Express is the primary path for communicating with Beagle. The link between the two craft was thoroughly tested unlike the communications route using Odyssey and Jodrell, officials point out. Mars Express will be positioned around the planet to begin looking for Beagle on January 4.

Other possible "blind commands" include telling the lander to open its top lid and redeployment of the solar panels in case those automatic post-landing events failed to occur as planned.

"These are good ideas to test but we also have to be very careful within the process of doing them that we don't disrupt the baseline systems that are already installed," Wells explained. "So the exercise now is to do a risk evaluation of these blind commands, seeking all the time to preserve the integrity of the baseline systems. So that is a careful balance."

"We have a model of this spacecraft. So anything that we want to try like this, the sensible thing is try it (on the model) and see what happens," said Colin Pillinger, the Beagle 2 lead scientist.

Meanwhile, Beagle officials have wondered if Odyssey's communications equipment used in the lander search could have been damaged by solar flares in late-October.

"We have asked JPL to look back into their housekeeping data to see if they can confirm that their transceiver on Mars Odyssey is working," Wells said. "We are looking to get a ground pattern from Mars Odyssey, probably picking it up with the Stanford telescope. So that is another line of investigation that is underway."

One of Odyssey's science instruments -- a radiation monitoring device -- stopped working during the intense solar storms.

"That is the reason why we have asked the Odyssey team to re-check the performance of their transceiver," Wells said.

Scenarios that the team isn't studying are "bad day" situations such a catastrophic problem during the fiery entry into Mars' atmosphere or a mishap with the parachutes or balloon-like airbags.

Despite the risky nature of entry, descent and landing -- only three landers sent to Mars have survived -- Pillinger said Beagle's system should have worked.

"We tested it and tested it again. We had a high degree of confidence in it."

Prior to arrival at Mars, the European Space Agency warned of some situations that would doom Beagle.

"An incorrect alignment of the lander could mean it burns up in the atmosphere. The parachutes could fail to deploy, plunging Beagle 2 into the surface at great speed. The balloons could become detached, or get punctured, again possibly causing Beagle 2 to crash."