Nasa has abandoned its attempts to locate the Mars Polar Lander (MPL), which landed on the Red Planet last month.

Mission leader Richard Cook said the MPL was definitively lost and that all efforts to trace the probe had been halted.

The last effort to communicate with the three-legged lander ended at 1600 GMT. "We didn't see anything," said Cook.

Now, space agency scientists and engineers will focus on what could have gone wrong and how to avoid the same mistakes in the next mission.

Nasa lost contact with MPL just as it entered the Martian atmosphere last month.

Nasa has yet to give any reason for the disappearance of the $165m craft.

MPL should have landed at the Martian south pole on 3 December, 1999, to look for signs of water. But there has been total silence ever since the final approach.

Crash theory

An unnamed source at Lockheed Martin Astronautics has said it may have crashed down a mile-deep canyon on the planet's surface.

This theory is based on what a Nasa website calls the probe's "probable" touchdown position, which was inside the planned landing area but near a steep-sided gorge.

However, Richard Zurek, a MPL project scientist, described the theory - first published in the Denver Post - as "premature".

He said the crater theory was just one of several scenarios still being investigated.

Nasa tried to locate MPL using cameras on board the orbiting probe Mars Global Surveyor, which was scanning the planet's surface.