In 1997, NASA's Pathfinder began a new era in Mars exploration when it touched down and, along with its tiny rover, Sojourner, explored the Martian surface for the first time in 20 years. In December 1999, a new NASA spacecraft will land on Mars, to be followed by several more missions over the coming decade. In The Mystery of Mars, former astronaut Sally Ride and science teacher Tam O'Shaughnessy draw on the latest Pathfinder data, as well as decades of study of Mars, to present a comprehensive overview of Earth's nearest neighbor. With its thin atmosphere, rocky canyons, extinct volcanoes, and icy polar regions, Mars has many things in common with Earth--and may have even had life. Comparing the two planets' evolution, geology, and geography, the authors explain what we know about Mars today and what we hope to learn about it in the future. With lavish color photographs, this engaging and accessible introduction to the Red Planet is the ideal guide to this new age of Mars research.