How did Mercury get such an enormous iron core? Why is its tectonic framework so different from any other planet or satellite? What is its crystal composition? Why is the crust so depleted in iron when the interior is so rich in that element? What are the polar deposits? Where do the elements in the exosphere come from? Mercury is a planet shrouded in mystery. Only 45 percent of its surface has been seen in any detail, and that was from the Mariner 10 flyby in 1974. Yet what is known only makes the planet more fascinating. New Earth-based observations have shed light on surface and exosphere compositions, and re-evaluations of the Mariner 10 data, using modern image processing techniques, show evidence for volcanic flow fronts, pyroclastics and other volcanic phenomena not seen before. This ground-breaking book not only chronicles what has been discovered, but looks ahead to what has yet to emerge. An accompanying CD contains all the best Mariner 10 images, including the data for each image, photomosaics and maps.