Alien Worlds: Your Guide to Extraterrestrial Life

Gr 4–6—After a brief overview of star life cycles, habitable zones, and how scientists conduct the search for Earth-like planets, the book presents the ecosystems and possible life forms of several imaginary planets. These worlds are based on actual planets observed outside our solar system, and the author makes clear connections between a given planet's characteristics (higher gravity than Earth, for example) and the effects on the alien life that evolved there (six-legged creatures reduce the weight load per leg). However, the transition between facts and fantasy is abrupt and may leave young readers confused about which content is real science and which is, as the book says, "scientifically based speculation." Readers with no background in the topic would be better served by the straightforward explanations in Mark Brake's The Alien Hunter's Handbook, which has a similarly jaunty, humorous tone. The digitally painted images, some based on polymer clay models, are not up to par with National Geographic's usual stunning photography but will be fun for browsers and fans of monster movie special effects. Back matter includes a complicated clay modeling project and extensive Web and print resources.—Sarah Stone, San Francisco Public Library