Updated throughout for the most current and authoritative content and art available. New coverage includes searching for planets outside our solar system; the possibility of life on Mars and Jupiter's moon Europa; Galileo's data on Ganymede and Europa; and the latest studies on the possibility that comets brought water and complex molecules to Earth. Includes a CD-ROM containing electronic html version of text with hyperlinks, exclusive animations, videos, an interactive study guide, and the Microsoft Explorer web browser.