Why is the Phoenix spacecraft a lander instead of a rover?
Despite the success of Mars Pathfinder and the Mars Exploration Rovers, the Phoenix mission will use a lander because it is simply a different type of mission. The rovers were designed to study rocks at different locations, looking for evidence that the liquid water once flowed on the surface of Mars. Unlike the rovers, which were hunting for evidence of water at points along the Martian surface, the Phoenix lander knows exactly where to go to find water. To reach it, however, the spacecraft must dig down below the surface. The Phoenix lander is going to an area of Mars where water is believed to exist in the form of ice just below the surface. This water ice is probably spread fairly uniformly throughout the northern plains so the lander should be able to uncover ice wherever it lands.
