Book excerpt: The next frontier in space exploration is Mars, the red planet--and human habitation of Mars isn't much farther off. Now the National Geographic Channel goes years fast-forward with "Mars," a six-part series documenting and dramatizing the next 25 years as humans land on and learn to live on Mars. This companion book to the series explores the science behind the mission and the challenges awaiting those brave individuals. Filled with vivid photographs taken on Earth, in space, and on Mars; arresting maps; and commentary from the world's top planetary scientists, this fascinating book will take you millions of miles away--and decades into the future--to our next home in the solar system.