LONDON – Europe's first Mars probe remained silent for a third day Saturday, but scientists clung to the hope that the Beagle 2 (search) spacecraft had landed safely on the Red Planet and would respond to a call from its mother ship in about a week.
The British-built Beagle was turned loose by the Mars Express (search) more than a week ago and was scheduled to land on the surface of Mars on Christmas Day and begin searching for signs of life.
But repeated efforts that began Thursday to pick up a signal from the probe, using the powerful radio telescope at Jodrell Bank Observatory in England and NASA's orbiting Mars Odyssey (search), have failed.
Late Saturday, the Jordrell Bank telescope struck out for a third straight day after scanning Mars for two hours. The NASA (search) spacecraft had similar luck earlier in the day.
"There is no sign from Jodrell," said Gill Ormrod, spokeswoman for the British government's physics and astronomy research agency.
Scientists in California joined the search for Beagle II, using a 150-foot dish antenna at Stanford University to listen for transmissions from the probe.
"We looked. We didn't see anything," said Michael Cousins, principal engineer at SRI International, a nonprofit research company that operates the dish.
Although scientists experienced some technical difficulties, Cousins said he believes the dish at Stanford would have picked up the signal if the Mars probe were transmitting properly.
Scientists now hope Mars Express will be able to contact Beagle once it enters its correct orbit Jan. 4.
"We haven't yet played all our cards," David Southwood, the European Space Agency's director of science, said earlier Saturday. "The baby, we believe, is down on the surface and the mother is very anxious to get in touch."
Mars Express was designed to beam back data gathered by Beagle, and Pillinger said its communications were specifically set up to hear the probe's transmissions.
In the coming days, controllers must change Mars Express' orbit from a high one around the equator to a lower polar orbit that will let it establish contact with the probe.
"With Mars Express we will be using a system that we have fully tested and understand," Southwood said. "I'm not writing it off right now and I don't think anyone should. We're hanging in there."
The scientists have maintained an optimistic line in the face of repeated disappointment and hope the probe touched down safely, aided by a parachute.
The 143-pound Beagle, shaped like an oversized pocket watch, was supposed to unfold its solar panels and transmit a signal confirming its arrival within hours of landing. But Jodrell Bank has twice scanned the planet's surface in vain, and Mars Odyssey has failed to pick up a signal in three overflights.
Scientists believe the probe may have landed off course in an area where communication is difficult. They say its antenna may not be pointing in the direction of Odyssey and fear Beagle's onboard clock has suffered a glitch, resulting in the probe sending signals at the wrong times.
Getting a working spacecraft to Mars has proven frustratingly difficult. Several vehicles, most recently NASA's 1999 Mars Polar Lander, have been lost on landing. The Soviet Mars-3 lander touched down safely in 1971 but failed after sending data for only 20 seconds.
Working in tandem, the Beagle and Mars Express are meant to look for signs of past or present life on Mars.
Beagle has robotic arm to take soil and rock samples, including a grinder to clean weathered surfaces and a drill to probe inside rocks.
Mars Express is expected to orbit overhead for at least a Martian year, or 687 Earth days, probing as deep as 2 miles below the surface with a powerful radar in its search for underground water. It also will map the surface with a high-resolution stereo camera.