The commands were sent at 10 a.m. PST today. They will instruct the lander, if it is operating, to send a signal directly to Earth to the antenna at Stanford on Wednesday, January 26, at approximately 1 p.m. PST.

The Stanford receiving station will listen again during the window on Wednesday to see if it picks up a signal that could originate from Mars. The results of this test will not be immediate and it will take the team several days to process the data.

Mission managers sent commands several times in December and January instructing Polar Lander to send a radio signal to the 45-meter (150-foot) antenna at Stanford.

Although no signal was detected in real-time, the team in charge of the Stanford antenna says that after additional processing of the data they may have detected a signal that could have come from Mars during tests on December 18 and January 4.

Because the signal was so weak, it took several weeks for the Stanford team to process their data and reach this conclusion.

"This week's test is a real long-shot, and I wouldn't want to get anyone too excited about it," said Richard Cook, Polar Lander project manager at NASA's Jet Propulsion Laboratory, Pasadena, CA.

"The signal that the Stanford team detected is definitely artificial, but there are any one of a number of places it could have originated on or near Earth. Still, we need to conduct this test to rule out the possibility that the signal could be coming from Polar Lander."

If in fact the signal were from Polar Lander, two failures would have had to occur.

First, the lander's X-band radio that it would use to transmit directly to Earth would have to be broken. Second, there would have to be a problem somewhere in the relay with Mars Global Surveyor that prevented the signal from being picked up and relayed by the orbiter.

It is unlikely that a broken transmitter on the lander could be fixed, and unclear whether a problem with the relay could be resolved.

Although the Stanford data from the previous tests took several weeks to process, the team expects to have results within several days now that they know what they are looking for.

Even if the signal were coming from the lander, there is little hope that any science could be returned. However, it would give the team a few more clues in trying to eliminate possible failure modes.