A robotic arm on NASA's Phoenix spacecraft, which landed on Mars Sunday night, is the key to discovering whether the planet can support life.

The seven-and-a-half foot long arm has an attached scoop and drill bit that will dig up Martian ice and dust on the northern pole of the planet, according to Matthew Robinson, Robotic Arm Flight Software Engineer with the Jet Propulsion Laboratory. The collected material will be analyzed onboard the Mars Lander and the results sent back to Earth.

"The robotic arm is basically the key to this mission," said Robinson. "None of it is any good if you don't have a robotic arm to bring in samples. We'd be able to get pictures but what excites me is acquiring a sample and processing it, because that gives us a whole new set of knowledge. We're not looking for life itself. We're looking for the elements that support life. We couldn't do it without the arm."

The robotic arm, which weighs 20 to 30 pounds, has four joints. One is an azimuth joint that allows the arm to rotate around the base. Another is an elevation joint that enables the arm to be raised and lowered. The third is a double-jointed elbow and the 3 to 4-inch-wide scoop is attached to the last joint.

During the spacecraft's takeoff and flight through space, the arm was restrained by a series of latches. The robot had to endure several G forces of acceleration during akeoff, hurtling through space at thousands of miles an hour. Then it endured the heat and turbulence of touching down on the Martian surface. Robinson noted that out of 11 missions to Mars, only six spacecraft have successfully landed on the surface.

"The robotic arm was designed to be able to take the types of vibrations and G forces expected, but even still you're concerned," said Robinson. "You work with it so much, it feels like a child. You know you've done your best and it can handle it, but you're still anxious about your baby."

The Mars Lander is on a one-way mission, and is expected to gather and analyze samples for three months. After that, Robinson explained that the planet's temperature will drop well below the current safe range of minus 170 degrees Fahrenheit to 32 degrees Fahrenheit, causing the Lander to freeze up and stop working.

Until that point, earthbound software programmers like Robinson will send daily code feeds to Mars to guide the robotic arm as it gathers samples. Robinson explained that they developed their own software program using C code. Every day they write, test and beam new code sequences to the Mars Lander to run the robotic arm. They send the code from ground-based radar dishes to two of the three orbiters circling Mars. From there, the code is beamed down to the spacecraft on the surface.

The whole sequence takes about 20 minutes, according to Robinson. Then 12 to 16 hours later, the Mars Lander sends a report on its efforts back to earth.

As of Thursday morning, the ground team had started uploading software for a third day. The first day's code was programmed simply to check the temperature on the Martian surface. Then the second day, the code had the Lander remove the clamps from the robotic arm so it could unstow the hardware.

Robinson noted that two Viking Landers sent to Mars in the 1970s the used robotic arms, though they didn't have nearly as much freedom of movement as today's arm. Then in 2000, NASA sent up the MER Rover, which had a robotic arm that used a microscope for close ups of surface material but no scoop or analysis capabilities.

Last March, the space shuttle Endeavour launched to take the pieces of a 3,400 pound, 12-foot-tall robot with a 30-foot wingspan to the International Space Station. The US$200 million robot -- Dextre -- is expected to take on most of the maintenance jobs required outside of the space station, cutting back on the number of dangerous space walks the astronauts must make.