Our solar system contains bodies which come in a variety of sizes. They are also very diverse in their physical and chemical makeup. These bodies---that is, asteroids, comets, and planets---wil be explored in great detail by NASA during the next century. By understanding what these celestial bodies are made of, whether or not they contain life, and how they were formed, we will be able to understand not only the origins of life here on Earth but also about the origin of the universe.