In this book about the outer reaches of our solar system, readers discover many intriguing facts. For example, the outer planets are separated from the inner planets by the asteroid belt. And, in addition to discovering Jupiter's moons, Galileo, in the early 17th century, observed the phases of Venus and made careful studies of sunspots. Readers also learn why humans could never live on one of the gas planets. The physical and chemical features and movement of the outer planets and their moons are detailed.