On Monday night, NASA had hoped to catch a glimpse of the surveyor from the camera on the new Mars Reconnaissance Orbiter. But the orbiter failed to spot it.

Now NASA will try an even less likely search effort. Engineers will send a signal to the silent spacecraft, asking it to turn on a beacon on one of the two Mars rovers below. If the rover beacon turns on, NASA could figure out where the lost Mars Surveyor is, said project manager Tom Thorpe.

"While we have not exhausted everything we can do ... we believe the prospect for recovery of MGS is not looking very good at all," said Fuk Li, Mars program manager at NASA's Jet Propulsion Laboratory in Pasadena, Calif., which controls the probe. "We're still holding out some hope."

NASA will keep trying small-scale communications efforts. Experts believe the surveyor, which lost contact Nov. 2, probably developed a problem with a device that moves solar panels causing it to lose communication.

The entire Mars Global Surveyor program cost $247 million, including launch expenses and a decade of in-flight operations. NASA had just approved a two-year mission extension for $6 million a year.

Launched on Nov. 7, 1996, the probe gave scientists the best topographic map of any planet in the solar system, said Cornell University astronomer Steve Squyres, who didn't have an instrument on board the probe but was part of NASA's scientific review team.

The probe gave Earth its first detailed views of massive dust storms and gullies. It also revealed a new mystery about Mars: It once had a magnetic field.

The low-cost probe rose "from the ashes" of a dramatic Mars failure, Squyres said. In 1993, the $813 million Mars Observer disappeared just before getting to the planet. Most of that probe's instruments were built again and included on the Mars Global Surveyor.

Christensen called the global surveyor "a workhorse" because of its numerous and diverse scientific instruments.

"It really has opened up new vistas of Mars that we hadn't the foggiest notion of," said Arizona State University geologist Ron Greeley.

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