By BBC News Online science editor Dr David Whitehouse

Engineers are looking into the possibility that a flaw in the design of Nasa's Mars Polar Lander (MPL) may have caused its engines to cut off prematurely when it was descending to the Martian surface.

This alarming suggestion is one of several possibilities under investigation into why the spacecraft has not made contact since 3 December despite strenuous efforts by the world's largest radio telescopes to pick up a signal.

Sam Thurman, MPL's flight operations manager at Nasa's Jet Propulsion Laboratory, said: "The problem has been identified with the design. That's one of several possible causes of loss of mission that have been identified during the investigation."

Future missions

Two review boards are looking into various failure possibilities and their implications for future missions to the Red Planet.

Other suggestions for the loss of MPL include:

• the spacecraft landed on the steep side of a canyon and toppled over;
• its complicated descent system thrusted unevenly;
• its radio broke down.

The latest suggestion is that jarring during descent, possibly from the release of the craft's back shell, might have triggered an early shutoff of the engines that were supposed to control and slow the lander's fall. This would have caused it to drop uncontrollably to the surface.

MPL's thrusters were designed to cut out after one of the probe's three legs made contact with the ground triggering a switch. But shutoff could have occurred as high as 40 metres (130 feet), meaning that it would be severely disabled when it crash landed.