After more than a month of searching for a signal from NASA's Mars Polar Lander, mission controllers have given up hope of finding it .

The Mars Polar Lander was on a mission to Mars to study its atmosphere and search for water, something that could help scientists determine whether life ever existed on Mars.

Polar Lander was to have touched down December 3 for a 90-day mission. It was to land near Mars' south pole.

The lander was last heard from minutes before beginning its descent.

The last effort to communicate with the three-legged lander ended with frustration at 8 a.m Monday.

"We didn't see anything," said Richard Cook, the spacecraft's project manager at NASA's Jet Propulsion Laboratory.

The failed mission to the Red Planet cost the American government more than $200 million dollars. Now, space agency scientists and engineers will try to find out what could have gone wrong. They do not want to make the same mistakes in the next mission. Controllers have been testing dozens of different scenarios to try and explain what might have happened to the lander.

Nobody knows exactly what happened to the lander, but there are several theories.

The Mars Polar Lander could have touched down on the side of a canyon and toppled over. Some people think the lander could have exploded before entering the atmosphere. Others say its radio systems might have failed, or that the lander could have sunk into Martian dust.

NASA sent a spacecraft called the Mars Global Surveyor to take high-resolution images of the landing site to search for signs of the lander. NASA hoped the orbiter would spot the lander's parachute or shadow. But so far attempts to capture a picture of the lander's parachute have been unsuccessful.

Another lander and orbiter are scheduled to launch next year, but at least part of the mission is now in doubt.

"The orbiter for sure will happen. There's no issue there," Mr. Cook says. "The lander they're still talking about."

The Polar Lander Spacecraft was 1.06 metres tall by 3.6 metres wide. Its total weight was 576 kilograms.

1. Who was on a mission to Mars to study its atmosphere and search for water, something that could help scientists determine whether life ever existed on Mars?