A third attempt by NASA's orbiting Mars Odyssey - at about 1:15 a.m. EST Saturday - made no contact with the Beagle 2, which was supposed to have landed at 10 p.m. Wednesday. It should have started emitting its signal within a few hours.
Britain's Jodrell Bank Observatory, which has twice scanned the Martian surface with its huge radio telescope, has also failed to detect a signal from the tiny lander, which was sent to Mars to search for signs of life.
Chief Beagle scientist Professor Colin Pillinger has kept an optimistic stance in the face of headlines like the one from the Daily Star newspaper, "The Beagle is Stranded." He appeared more subdued Saturday morning after the latest failure.
He clearly held hope for the Beagle's survival, and was banking on communications help from the Beagle's mother ship, The Mars Express, which is in orbit around Mars and due to start communications Jan. 4.
"We reckon our best chance of a communication with Mars is to wait until Mars Express is available for use," Pillinger told a news conference.
"Mars Express is, after all, our primary route for communication. ... We have to consider it the best way of talking to Beagle 2," he said, referring to the Beagle's mother ship, which is in orbit around Mars and due to start communications Jan. 4.
David Southwood, the European Space Agency's director of science, also said he was not "writing off" the Beagle "and I don't think anyone should."
"I'm pretty sure it's down on the surface of Mars," he told the British Broadcast Corp. "We have quite a few more chances ... There may be things on Beagle we can fix by sending down the right commands from Mars Express."
The scientists have said Mars Express, which carried Beagle into space and set it loose a week ago, could offer the best chance to get a signal because it is designed to beam back data gathered by the probe.
The Mars Express went into orbit Thursday but controllers must change its path from a high elliptical one around the equator to a lower polar orbit that will let it establish contact with Beagle 2.
Southwood told the news conference there was still a "good chance" the mother ship will make contact with Beagle 2.
"We haven't played all our cards, and we'll then be using a system we absolutely know has been tested and we fully understand," he said.
Possible explanations for Beagle's failure to call home include an off-course landing in an area where communication with Mars Odyssey was difficult, if not impossible. Also, transmission from the lander's antenna could be blocked from reaching Mars Odyssey or the ground-based telescopes, the agency said.
Two U.S. Viking spacecraft made it to Mars in 1976, while NASA's Mars Pathfinder and its rover vehicle Sojourner reached the surface in 1997.
Several vehicles, most recently NASA's 1999 Mars Polar Lander, have been lost on landing. The Soviet Mars-3 lander made a soft landing in 1970 but failed after sending data for only 20 seconds.
The $370 million European mission aims to search for evidence of life on Mars. Beagle was supposed to have plunged into the Martian atmosphere for 7 1/2 minutes on its way to a landing softened by parachutes and gas bags. Once there, its antennae were to flip open and begin transmitting home.