Gas giants are massive planets that are made of mostly helium and hydrogen gas. The massive planets are bigger than many of the other planets in our solar system, and the biggest of them all is Jupiter! Not only is Jupiter the biggest gas giant, it's also the biggest planet in our solar system. Young astronauts will love learning the mysteries of this strange planet while comparing it to our own home world. With photographs pared with approachable text, young readers will love learning about Jupiter!