How did the solar system form? Are we alone in the Universe? What are alien atmospheres made of? These questions can be answered by studying the solar system's vast family of satellites.

From the first human footsteps on another world to the most distant spacecraft landing in history, our neighbourhood of moons has always played a central role in our exploration of the planets. For an introductory astronomy course, try The Open University course S194 Introducing astronomy. www.open.ac.uk