This chapter has several goals. The first is to provide some general historical background on how Mars was perceived before spacecraft exploration started with the launch of Mariner 4 in 1964. The second goal is to provide an overview of what conditions are like on Mars today. Most of the book concerns the record of past events as preserved in the landscape and in the rocks at the surface. Although conditions may have been different in the past, those that prevail today provide strong constraints on how we interpret that past record. A third purpose is to give a brief overview of topics that are important for our understanding of the planet, but which are a little off the main theme of the book, which is to describe the major geological features of the planet and their origin. A brief description of the present atmosphere is included here, for example. We also include a section on martian meteorites. These are both huge topics with a vast literature, and no attempt is made in the book to treat them comprehensively. A fourth aim of the chapter is to provide a short geological overview so that the subsequent, more detailed chapters can be read in light of a general knowledge of the planet's geology. Most geological topics are just touched upon here and referenced to later chapters.

Telescopic observations

Mars is the fourth planet from the Sun.