Radio antennas in California, England and the Netherlands listened on Friday for a signal from the landers UHF transmitter.

However, analysis of the data completed on Monday turned up no trace of the spacecraft, which landed on Mars more than two months ago. Any and all artificial signals the dishes did pick up were terrestrial in origin.

"They have been working around the clock to help us and we are grateful for their efforts," said Richard Cook, project manager for the Mars Polar Lander at NASA's Jet Propulsion Laboratory (JPL).

Polar Lander Flight Operations Manager Sam Thurman said in an interview last week the opportunity was the best yet to hear from the spacecraft on the odd chance it survived the landing.

NASA last heard from the spacecraft on December 3, just minutes before it was supposed to enter the martian atmosphere at the onset of what would have been a 90-day mission to probe the planets south polar region.

NASA geared itself up to send more commands the 181 million miles (290 million kilometers) to the spacecraft late Monday, instructing it to contact Earth at a specific frequency. It will coordinate an international attempt to listen again on Tuesday, this time adding a radio array in Italy to the mix.

The second round of observations will eliminate any remaining uncertainty about the operational status of the landers batteries. On Tuesday, the various antennas will conduct two 30-minute listening windows with a two-hour "cooling down" period in between.

It could take a full week to sift through that data for a weak signal. Scientists have said they are listening for the equivalent of a cellular telephone call made from Mars.

"It strikes me as very unlikely that we have a signal from the lander, but if there is any chance weve got to look for it," said Carl Pilcher, who as NASAs science program director oversees the space agencys solar system exploration efforts.

After Tuesdays data has been combed through, the Europeans will likely bow out of the search, a JPL spokeswoman said.

However, NASA may deputize the enormous Arecibo Observatory radio dish to assist in listening for the Polar Lander later this month, when Mars comes into view of the Puerto Rican facility.

NASA had proclaimed the lander dead and lost on January 17. However, a team of Stanford University scientists announced several days later that they had received what appeared to be artificial signals from Mars on two separate occasions.

Since then, NASA has sent multiple commands to the lander, pausing each time to then listen for a response. Nothing has been heard since the renewed efforts began.

NASA is anxious to hear a signal, no matter how faint, from the Mars Polar Lander because it would help in the agencys efforts to divine why the mission failed.

The lander was the second Mars-bound spacecraft NASA lost in 1999. The Mars Climate Orbiter was destroyed in September when it came too close to Mars upon entering orbit around the Red Planet.

The double loss will likely have a large impact on the shape and timing of NASAs ambitious Mars exploration program. Pilcher said NASA would likely begin to announce those changes in late March.