By BBC News Online science editor Dr David Whitehouse

Nasa is finally about to give up its attempts to contact the ill-fated Mars Polar Lander (MPL) spacecraft.

MPL was to have landed at Mars' South Pole on 3 December but the last that was heard from it was a routine transmission sent as it began the final phase of its descent. Scientists think that the most likely explanation for the silence is that it tumbled into a hole.

Despite the virtually certain loss, the MPL flight team have continued their efforts to regain communications with the lander. The final set of planned commands were transmitted late last week to place the spacecraft in what is called a "UHF safe mode".

Over the past week the Mars Global Surveyor (MGS) spacecraft, which is in orbit around Mars, has also been listening for the MPL. All attempts will end on Monday, at which time MPL will be officially declared lost.

Vision impossible

Attempts to capture a picture of MPL's parachute from MGS have so far been unsuccessful. However, scientists have just obtained additional information from MPL's navigation data, which includes data up to the day of landing.

This means that the search area for the parachute has shrunk considerably. MGS has already begun looking at this area with high-resolution and the new images are being inspected.

Nasa has had two recent Mars missions go badly wrong. As well as the MPL loss, the Mars Climate Orbiter probably burned up in the Martian atmosphere in September after project scientists mixed Imperial with metric measurements.