Despite the failure so far to contact the probe, few experts are willing to write it off just yet. Some say "Beagle's" clock may have been accidentally reset and that its signals are being sent at the wrong times. Another explanation is that its antenna may be pointing in the wrong direction, following a landing on a steep slope.
Duncan Fortune heads the space software group QinetiQ, which is responsible for the communications equipment on both the "Beagle" and "Mars Express," the orbiting European spacecraft that ferried "Beagle" to Mars. "It certainly is a possibility. The system that was designed for 'Beagle' can see a spacecraft passing within 60 degrees of overhead, but if the spacecraft is very heavily tilted over to one side, or it is at the bottom of a crater, then that will clearly cut down the angle," he said.
The crater theory emerged after the latest pictures of "Beagle's" landing area revealed two previously unknown craters, each nearly 1 kilometer in size. Unfortunately, the photographs -- taken by the orbiting U.S. spacecraft "Mars Odyssey" -- were processed only after "Beagle" had already landed. The possibility that "Beagle" ended up either on the rim or inside one of these craters cannot be excluded.
Some observers have simply concluded that the $375 million "Beagle 2" likely crashed on landing. After all, two-thirds of all the probes sent so far to Mars have failed. But project scientists on "Beagle" say they have confidence it survived its fiery descent through the Martian atmosphere, its parachute braking, and a landing inside inflatable airbags.
Colin Hicks, director-general of the British National Space Centre, explained that every component of the spacecraft had been thoroughly tested. For example, the parachute system. "With about nine months to go to the completion of 'Beagle 2,' we found that we had to slow it down more than we had expected, and we had to completely redesign the parachute and have it remade," he said. "That parachute worked perfectly in every test we did."
Fortune, the communications expert, says there's another reason for not giving up. A signal to reset "Beagle's" internal clock was sent to the spacecraft on 30 December. Should the spacecraft fail to get a response from Earth after 10 communication attempts, it will switch to transmitting twice a day, and from 5 January every 10 minutes. So Fortune says he remains optimistic.
"As time progresses, 'Beagle' will realize itself that something has gone wrong with the link, and tries to do its best to help us in the recovery operation. We were disappointed we did not manage to pick 'Beagle' up with 'Odyssey,' but we will carry on until we see a signal," he said.
The "Mars Express" spacecraft is due to settle into its final orbit next week (7 January). Then it should be in a position -- as low as 200 kilometers from the Martian surface -- to pick up even the weakest signal from "Beagle."
If "Beagle" remains silent, however, British scientists say they will turn their attentions to the European Space Agency's "Mars Express" mission. The spacecraft is set to photograph the entire surface of Mars at a high resolution, map global mineral composition, study the atmosphere, and determine the makeup of the planet's outer crust, including the presence of any underground water.
Meanwhile, there are two roving vehicles on the way to Mars, launched last year by the U.S. space agency NASA. NASA calls them the most sophisticated robots ever sent to another planet.
The six-wheeled rovers -- which together cost $820 million -- are to travel about 1 kilometer on the surface, examining everything along the way for some three months. They carry an array of instruments to test the soil and rocks for signs of water and previous microscopic life, as well as stereoscopic cameras to obtain spectacular panoramas of the Martian surface.
The new rovers are much larger than the "Sojourner" robot that was the focus of NASA's successful 1997 Pathfinder mission. The new rovers weigh around 175 kilograms each, compared to "Sojourner's" 11 kilograms.
Both craft are designed to go through a similar descent and landing sequence to that of "Beagle 2," including bouncing within inflatable airbags upon landing. And, as Duncan Fortune notes, if there are any communications problems, the experiences gained from the "Beagle" mission may help.
"Both 'Mars Express' and 'Odyssey' are fully compatible with 'Beagle,' as incidentally are the two American rovers. So, the five elements either in orbit or on the surface of Mars are all fully compatible with each other. The only real difference is that the systems for 'Mars Express' and 'Beagle' were developed together, so there was a lot more testing done," Fortune said.
The first U.S. rover, named "Spirit," is due to land early Sunday (4 January) morning CET in an enormous crater called "Gusev" that may once have been a lake. The second rover, "Opportunity," is expected to land three weeks later, on 25 January, on the other side of Mars at a site called Meridiani Planum, where deposits of water-formed minerals have been detected.