Author William Hartmann has fully updated this text, which retains a comparative approach to the principles of planetology, including organization by physical topic rather than by planet. This unique approach promotes an understanding of the unifying principles and processes that cause similarities and differences among the moon and planets. This edition features findings and photos from Mars Odyssey and Mars Global Surveyor missions as well as information on new discoveries about Mars, such as underground ice and possible glacial features. The author also includes new results about the "Tagish Lake fireball," material from the landing of the NEAR spacecraft on asteroid Eros, and updates on satellites of Jupiter and Saturn. The text's unique math boxes provide flexibility to teach planetary science at a descriptive level or at a moderately advanced level involving algebra and elementary calculus.