Scientists began releasing the robotic arm on NASA's new Mars spacecraft, one day late because of a radio problem.
The Phoenix lander is in excellent shape, project manager Barry Goldstein said.
The robot will spend three months exploring the planet's northern arctic region, searching for evidence of whether the planet could have supported life.
Phoenix's arm will eventually dig into the soil, seeking ice believed to be inches below the surface.
The $420-million mission is led by University of Arizona, Tucson, and managed by NASA's Jet Propulsion Lab in La Canada Flintridge.