The US space agency (Nasa) says the veteran Mars Global Surveyor spacecraft is probably lost and irrecoverable.
Mars Global Surveyor was launched in November 1996 (Image: Corby Waste/Nasa)
The orbiter entered a "safe mode" as it struggled to control a solar panel, and engineers have not been able to contact the probe since 2 November.
Nasa will use the Rover Opportunity on the surface of the Red Planet to try to speak to the 10-year-old spacecraft in the next couple of days.
However, mission officials concede they are not expecting success.
"While we have not exhausted everything that we could do, we believe the prospect of recovery of MGS is not looking very good at all," said Fuk Li, Mars exploration programme manager at Nasa's Jet Propulsion Laboratory (JPL) in Pasadena, California.
"However, MGS has been a good friend; it's had an illustrious career, the data it has collected has taught us a lot about Mars and it will continue to teach us a lot about Mars.
"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."
The rover will use a low-power UHF antenna to try to contact MGS in the next couple of days. If it gets a reply, it will relay that response to Earth.
The problem for Nasa is that its knowledge of MGS's precise orbital position has deteriorated because tracking has not been possible. As the period of silence continues, the uncertainty will grow and make detection or communication ever more difficult.
The concern for engineers is that the problematic solar panel is stuck in a position that means the spacecraft can no longer generate enough power to communicate.
"It's anybody's guess as to where that stuck panel is pointed, but we feel there's a good chance that we're getting enough power to maintain operations," said Tom Thorpe, project manager for Mars Global Surveyor at JPL.
Mars Global Surveyor was launched in November 1996, operating longer than any other Martian craft.
Carrying a powerful camera that has returned thousands of images, it has discovered features suggesting water once flowed on the desert world, mapped its mineralogy, and has surveyed potential landing sites for future surface missions.
The spacecraft is one of four spacecraft orbiting the Red Planet. Its companions include Nasa's Mars Reconnaissance Orbiter and Mars Odyssey, and the European Space Agency's Mars Express.
Mars Global Surveyor was originally launched as a $247m mission to study the planet's surface for one Martian year, roughly two Earth years. It was recently granted another two-year extension.
"We may have lost a dear old friend and teacher - Mars Global Surveyor," said Michael Meyer, Nasa's lead scientist for Mars exploration.
"MGS has generated a tremendous legacy, not only in the discoveries in hand but also in the future scientific surprises to be discovered from the ongoing analyses. All the data from MGS is in the planetary data system which is available to the world scientific community for study."