Extraterrestrial life hasn-t yet been discovered, but smiling cartoon aliens can be spotted throughout this otherwise nonfictional exploration of the solar system and space travel. Planets and other celestial bodies get anthropomorphic details (an asteroid wears eyeglasses; Saturn, with -more than sixty moons,- is shown juggling several of them), but even with these and other jokey images, Martin packs a substantial amount of information into spreads about the planets, moons, stars, and astronauts; several flaps are incorporated into the scenes, revealing additional facts and details. It-s an accessible, hands-on primer for astronomers in the making. Available simultaneously: The Animal World. Ages 4-8. (Apr.)