Asteroid formation and composition, illustration. At upper left is a large asteroid, surrounded by smaller asteroids. Larger asteroids are nearly spherical, and can develop a core, mantle and crust (composed of different materials), as shown in cutaway at upper right. Smaller asteroids are irregularly shaped and composed of the same undifferentiated materials throughout. Across bottom, the differences this causes in the results of impacts are shown. At lower left, an impact with a large asteroid releases fragments from the different materials found in the core and mantle. In contrast, at lower right, impacts with smaller asteroids results in a cloud of dust and rock debris with no differences in composition.