Want your students to REALLY remember the solar system? Have them CREATE an awesome solar system model/mobile. I guarantee they will love it. Mine did! All you need is a $1 bag of styrofoam balls from the dollar store for each student, a note of instructions, and they do the rest. A generic take-home note with instructions is included, as well as pictures. You'll be amazed how awesome they turn out. I did it with 3rd graders and the rest of the school was very impressed.
See them and read more about it on my blog at Tangled with Teaching