The most exciting new discovery in modern astronomy must surely be the detection of planets orbiting distant stars, but what kinds of worlds these new planets are is yet to be determined with certainty. In this imaginatively written yet solidly scientific work, planetary scientist John S. Lewis explains how planets form, what they are made of, and how scientists know what they know about both the planets in our solar system and those orbiting distant suns. From solidly grounded knowledge to the latest theories of planetary science, "Worlds Without End" is essential reading for everyone thrilled by the latest discoveries in astronomy.