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This computer graphic, using an image of the planet Mars, shows that the planet--like Earth--has a crust, a mantle and an iron core. NASA scientists say this conclusion from radio signals from the Pathfinder spacecraft is the first strong evidence Mars is not just a ball of rock. The image was released Wednesday, Oct. 8, 1997, by the Jet Propulsion Laboratory in Pasadena, Calif. The arrow indicates the direction of the spin access. (KEYSTONE/AP Photo/NASA/Jet Propulsion Laboratory/MALIN SPACE SCIENCE SYSTEMS)