Starry Night Pro Plus 6 is more than he could probably want but it is an outstanding piece of software. You can add your own bodies zoom out and see the orbits of all the planets and view asteroid and comet orbits. You can rotate the plane to see exactly where those orbits are. It's expensive though and the lower versions don't have the option to add your own asteroids or comets.

Redshift 6 Premium is much cheaper and probably a better alternative.

However check out both of these titles.