During its 422-million-mile flight from Earth to Mars after launching on Aug. 4, 2007, Phoenix relied on electricity from solar panels during the spacecraft's cruise stage. The cruise stage was jettisoned seven minutes before the lander, encased in a protective shell, entered the Martian atmosphere. Batteries provide electricity until the lander's own pair of solar arrays spread open. -Mission News
You can even check out the video of the Martian Arctic Plains!