One of the easiest solar system projects is to create a model similar to a mobile. You will need styrofoam spheres of different sizes, dowels, paint and twine. You will need a sphere for each planet and the sun. Use spheres that are most representative of the the proportional sizes of the planets. Paint each sphere according to the attributes of that planet and one for the sun. Using the sun as the center, create a mobile with the planets around the sun.