A key scientist on the project named those odds Wednesday, based on reports from radio telescope experts at Stanford University that possible candidate signals from the $165 million lander may have been detected. Follow-up work could verify that it is alive, but sickly.

"It would be a miracle if we get anything back from it but weve got to keep trying," said David Paige, principal investigator for the lander at University of California at Los Angeles. "Id say theres a 50-50 chance that the landers there. Thats close to where I am, personally."

Paige said, however, he was not sure "a good clear path" exists for getting data back from the craft.

If the three-legged lander did safely ease itself down onto the martian surface, Paige said its computer might have saved a set of pictures taken en route to its touchdown.

"Theres a chance that the data it took on the first day is still sitting there and ready to downlink," he said.

Establishing a radio link with the Polar Lander could mean that some data might be retrievable. Moreover, finding the lander intact would help to pinpoint what did go wrong, allowing NASA to better plan future exploration missions at Mars.

"Everything I can cross is crossed," Paige said. "This is like a soap opera, the kind where they kill off one of the main players, then they come back in a couple of weeks and you find out it was just a dream."

A 150-foot radio dish operated by Stanfords Space, Telecommunications and Radioscience Laboratory in Palo Alto, California has been putting an electronic ear to Mars, hoping to pick up signals from the lander, which failed to phone home after its expected arrival at Mars on December 3. When last heard from, it was headed for a perilous touchdown at Mars south pole region. Several high-resolution pictures of the landing site, which are still to be made public, confirm that the area was far more treacherous than scientists believed.

Very weak signals, perhaps from the lander, were detected at Stanford during tests on December 18 and January 4. Weeks of data crunching suggest that a signal -- artificial in nature -- came in from somewhere, but its origin remains in doubt.

Stanford laboratory senior engineer, Ivan Linscott, said researchers have not found any signals that are good candidates for the lander.

"We have some very weak, probably radio frequency interference candidates that we are continuing to investigate," Linscott said. "We have an additional run with the dish [Wednesday], to see if we can confirm the detection of a possible signal. At this time, the signals we see are just as likely due to radio frequency interference."

Paige remains optimistic, though, noting there are software programs inside the lander that could explain why the probe is giving Earth the silent treatment.

"It could have been listening to a large fraction of the commands that we have sent it so far," he said. "But its hard to say why its doing what its doing."