WASHINGTON, May 28 (Xinhua) -- U.S. Mars lander Phoenix, which touched down on Sunday at northern polar plains on Mars, successfully unstowed its robotic arm on Wednesday, according to NASA mission updates.

Early Wednesday, scientists leading Phoenix mission from the University of Arizona sent commands to move the lander's robotic arm for the first time after its touchdown.

This artist's concept depicts NASA's Phoenix Mars Lander after its planned touchdown on the arctic plains of Mars.

"It's a series of seven moves, beginning with rotating the wrist to release the forearm from its launch restraint. Another series of moves releases the elbow from its launch restraints and moves the elbow from underneath the biobarrier," robotic arm manager Bob Bonitz of NASA's Jet Propulsion Laboratory explained.

The robotic arm is a critical part of the Phoenix Mars mission. It is needed to trench into the icy layers of northern polar Mars and deliver samples to instruments that will analyze what Mars is made of, what its water is like, and whether it is or has ever been a possible habitat for life.

"Phoenix is in perfect health," JPL's Barry Goldstein, Phoenix project manager, said on Wednesday.