The Mars Polar Lander (MPL) lost by Nasa a month ago may have met its end in a catastrophic tumble down the sides of a canyon almost a mile deep.

Nasa has yet to give any reason for the disappearance of the $165m craft and has told project team members not to speak to the media.

But an unnamed source at Lockheed Martin Astronautics has broken cover and spoken out. A team at the company steered the craft to Mars.

There are "very high odds that MPL landed in a canyon about 1.3 km deep", the person told the Denver Post on Thursday. MPL would then have rolled over and may have broken up. The source said this had been known for two weeks.

"It's like dropping a chair on a steep hill. It's built to land, not to roll," the source said. "The odds of [landing] on a ground slope greater than 10 degrees was very small. The odds of landing on a ground slope greater than 15 degrees, forget it. Some estimates of the slope of the canyon sides are 20 degrees."

Landing odds

This version of the fate of MPL is based on what a Nasa website calls the "probable" touchdown position of MPL. This plots the landing site as 76.13 degrees south and 164.66 degrees east.

This is within the planned landing area but also on a steep-sided gorge. The team at Lockheed Martin did not know of its existence until two weeks after the failed landing.

The source said: "Two weeks later, we got [these maps and images] and it was like, 'Look at that hole!'"

The source thought that although the canyon was in the target area, the odds of landing there were too low to worry about.

'Premature' theory

Richard Zurek, MPL project scientist, described the Denver Post exclusive as "premature", and said the crater theory was just one of several scenarios still being investigated.

"There is a large crater in the western portion of the landing zone which contains rougher terrain than what we've seen elsewhere," Zurek told reporters.

He said that after flight controllers at Lockheed Martin had performed a fourth flight correction manoeuvre a few days before the lander reached Mars, scientists realised they were drifting west and toward the huge crater.

"We had planned a fifth and final correction for a few hours before the landing to push the lander more to the east, but we realised that manoeuvre would also push us too far to the south, so we chose to control the ... landing path. We expected we would have landed a bit north of the crater," he said.

Nasa's efforts to locate MPL are continuing with cameras on board the orbiting probe Mars Global Surveyor scanning the planet's surface. Its initial scan showed nothing, however.

It will continue the search for another two weeks before giving up. The best hope is the satellite will be able to take pictures of the MPL's 20-metre long parachute, a big enough object to be picked out by the satellite's cameras.

"If we find the parachute we will know that the lander is no more than a kilometre away because if everything went right the two would have separated one kilometre above the surface and there wouldn't be much distance between them when they came down," he said.