TUCSON (AP): The Phoenix lander is getting ready to flex its muscles on Mars.

The spacecraft successfully freed its 8-foot (2.4-meter) robotic arm from the restraints that kept it folded up and protected from vibrations during the launch and landing, scientists said Thursday. Preparations are now under way to partially flex the arm.

After scientists test the arm's joints at different temperatures over the next several days, they will tell Phoenix to use the camera on the arm to look at the lander's underbelly and take a picture of the terrain beneath it.

Researchers want to make sure the lander is stable so it won't tilt once the arm is fully extended, said Matt Robinson of NASA's Jet Propulsion Laboratory in California.

Phoenix landed near the north pole of Mars on Sunday, and scientists are spending the first week or more testing different parts of the spacecraft before the real work begins.

The robotic arm will be used to dig and scoop up ice and dirt. Scientists are seeking samples to determine if the ice ever melted, and experiments will look for traces of organic compounds considered the building blocks for life.

The three-month mission is led by the University of Arizona, Tucson, and managed by JPL.