NASA scientists are beginning to lose hope of re-establishing contact with their oldest Mars space probe, missing since Nov. 2.

"We may have lost contact with a dear old friend and teacher," Michael Meyer, lead scientist with the Mars Explorations Program, told reporters during a conference call on Tuesday.

NASA launched the Mars Global Surveyor in November 1996. The probe has spent the past 10 years in the near vacuum of space, returning more than 240,000 images of the red planet and providing scientists with a wealth of information about Mars's geology and meteorology.

While its mission was expected to end in early 2000, the probe's longevity meant NASA scientists were able to renew its mission year after year.

Among its many important accomplishments, Mars Global Surveyor has photographed young gullies apparently cut by flowing water and discovered water-related mineral deposits. Water is of course one of the elements needed to support life.

"It's changed our concept of the red planet," said Meyer. "Although it still looks cold and dry, we now know that recently Mars had water and had much more water in the distant past."

But on Nov. 2, the probe reported problems moving its solar panel and went into a pre-programmed backup mode. Since then, NASA scientists have been unable to "talk" with the Mars Global Surveyor, one of five active space probes in orbit around the planet.

"We have not exhausted everything we could do," said Mars Program Manager Fuk Li.

"We're still holding out some hope, but we are fully prepared in our hearts that we may never be able to talk to the spacecraft again."