That would account for the landers now month-long silence on the Red Planet, since it would not have known to contact Earth when engineers were listening for the craft.
"The last set of things we want to check out is if were not synched up, that the lander thinks its a different time than we do," said Richard Zurek, the missions project scientist.
The commands being sent Thursday will instruct the lander to switch on its UHF antenna for 20 minutes every four hours.
If all goes well, the Global Surveyor should pass overhead during one of those transmissions during the course of the 11-day experiment and pick up the signal, which it would then relay to Earth.
"It takes time to guarantee that happens at least once," Thurman said.
However, Thurman said the mission team has little hope of hearing from the lander.
"But we feel obligated to complete all contingency scenarios," he added.
Orbiter camera fails to find lander, so far
Meanwhile, an effort to photograph where the errant spacecraft might have set down on the surface of Mars has proved fruitless.
NASA has used the high-resolution camera aboard the Global Surveyor, a satellite in orbit around Mars since 1997, to aid in the search for the lander.
The orbiter completed imaging the landers most likely landing ellipse - an area about 40 square miles (100 square kilometers) in size - on Dec. 24. Never before has such a large swath of the martian surface been imaged in such fine detail, showing features as small as five feet (1.5 meters) across.
But in sifting through the images that make up the high-resolution mosaic of the targeted area, neither the lander nor its parachute has cropped up, said Michael Ravine, advanced projects manager for Malin Space Science Systems Inc., the San Diego builder of the Surveyors camera.
The lander would appear at most as only a few picture elements, or pixels, in those images, making it all but impossible to spot. Since its parachute is larger and brighter, however, it could conceivably be made out against the comparatively darker background.
"The parachute would have been the only thing big enough," Ravine said. "The lander could be in one of those pixels, but because of the noise, you couldnt be sure enough to point to any two pixels and say, Thats it, and not some other two pixels."
Zurek said JPL now wants to double the search area targeted by the camera.
First, however, the Global Surveyor will make a second attempt to image Mars Pathfinder at 1 p.m. EST on Sunday.
By imaging the Pathfinder, which successfully landed on Mars in 1997, engineers can check whether it is even possible to spot something as small as a lander from the Global Surveyors vantage point.
"We dont want to unduly spend time looking for something we cant possibly see," Zurek said. "It will be a demonstration of what is our true capability."
A Dec. 26 attempt to image Pathfinder was off by several miles (kilometers) because of an error in plugging in the Pathfinders coordinates, Ravine said.
Review panels to report in March
Given that NASA has little hope of ever hearing from the Polar Lander, the search now hinges on determining what went awry after the spacecraft plunged into the martian atmosphere, stepping into a silence that now seems permanent.
"At this point, were really trying to diagnose as best we can what went wrong," Zurek said.
Separate NASA review panels will deliver their reports on the loss in March.
The loss of the Polar Lander came just 11 weeks after the $125-million Mars Climate Orbiter failed to enter orbit around Mars.
Together, the two missions made up the $328-million Mars 98 project, the second installment in NASAs ambitious campaign to explore the Red Planet.
Under the program, NASA aims to send a pair of spacecraft to Mars every 26 months. The next mission, which uses a craft similar to Polar Lander, is scheduled for launch in 2001, although that will now probably be delayed.
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