You could make a diorama. Make pluto and its moons out of different size styrofoam balls. Paint the palls accordingly, then hang them from the top of the box with clear string or fishing string accordingly. Or you could make them out of molding clay, bake them till they are hard. Paint them, insert a wooden dowel in the bottom of the "planets and then place them on a wooden platform. That option requires a lot of work and tools such as a drill and wood glue.
Maybe you can use foam balls and make a diorama.
Make it out of paper mash ea stuff eh stuff us I love josiah