NASA is investigating whether incorrect software commands may have doomed the Mars Global Surveyor spacecraft, which abruptly fell silent last year after a decade of meticulously mapping the Red Planet.

The space agency said the theory is just one of several that may explain the probe's failure. NASA on Wednesday announced the formation of an internal review board to investigate why the Global Surveyor lost contact with controllers during a routine adjustment of its solar array.

John McNamee, deputy director of solar system exploration at NASA's Jet Propulsion Laboratory, said a preliminary investigation points to incorrect software commands uploaded to the spacecraft in June.

The software was aimed at improving the spacecraft's flight processors. Instead, bad commands may have overheated the battery and forced the spacecraft into safe mode, McNamee told scientists gathered Tuesday in Virginia to plan for future Mars missions.

An account of McNamee's speech was posted on the NASA watchdog site nasawatch.com, and it was confirmed Wednesday by Doug McCuistion, director of NASA's Mars Exploration Program.

Overheating problem

Records show there was an incorrect loading of software, which could have resulted in a cooling radiator for a battery being pointed at the sun, McCuistion said.

"It may have overheated and lost the battery, which then would not allow us to have adequate power to operate the spacecraft," McCuistion told AP Radio.

If the Global Surveyor's demise is traced to a technical error, the mistake raises questions about why engineers did not catch the problem before the software program was sent to the spacecraft.

McCuistion said the space agency will wait for the completion of the investigation before declaring an official cause of failure.

Before it failed, the Global Surveyor found strong evidence that liquid water recently coursed through two gullies on the planet.

The Global Surveyor, which lost contact with Earth in November, was the oldest of six active spacecraft on or circling Mars. NASA has made several unsuccessful attempts to locate the missing probe.

"We're declaring it most likely dead," McCuistion said. "I doubt we will see it again."

During its 10 years mapping the Martian surface, the Global Surveyor beamed back some 240,000 pictures, including the first detailed images of swirling dust devils and gullies.

Shortly before it failed, the Global Surveyor re-imaged thousands of gullies and found the strongest evidence yet that liquid water recently coursed through two of them. The discovery, which still needs to be confirmed, raises the possibility that Mars might harbour an environment conducive to primitive life.