The early part of the twenty-first century saw the completion of the reconnaissance of the Solar System by spacecraft. With the launch of the New Horizons spacecraft to Pluto in early 2006 and its expected arrival in 2015, spacecraft will have been sent to every planet, major moon, and representative asteroid and comet in our Solar System. With the return of data taken by spacecraft of these objects, the study of planetary surfaces passed mostly from the astronomer to the geologist and led to the establishment of the field of planetary geology. The term geology is used in the broadest sense to include the study of the solid parts of planetary objects and includes aspects of geophysics, geochemistry, and cartography. Much of our knowledge of the geologic evolution of planetary surfaces is derived from remote sensing, in situ surface measurements, geophysical data, and the analysis of landforms, or their geomorphology, the primary subject of this book.

In this chapter, an overview of Solar System objects is given, the objectives of Solar System exploration are outlined, and the strategy for exploration by spacecraft is discussed. In the following chapters, the approach used in understanding the geomorphology of planets is presented, including the types and attributes of various data sets. The principal geologic processes operating on planets are then introduced, and the geology and geomorphology of each planetary system is described in subsequent chapters. The book ends with a discussion of future missions and trends in Solar System exploration.