NASA's Mars Reconnaissance Orbiter passes over the planet's south polar region in this artist's concept illustration. NASA plans to launch this multipurpose spacecraft in August 2005 to advance our understanding of Mars through detailed observation, to examine potential landing sites for future surface missions and to provide a high-data-rate communications relay for those missions. The orbiter's shallow radar experiment, one of six science instruments on board, is designed to probe the internal structure of Mars' polar ice caps, as well as to gather information planet-wide about underground layers of ice, rock and, perhaps, liquid water that might be accessible from the surface. Phobos, one of Mars' two moons, appears in the upper left corner of the illustration.