From a planet with a hexagonal storm to the home of the solar system's largest volcano, our neighboring bodies are unique and fascinating locales. Where else would you find a place with days longer than its years? Humanity's understanding of planets has changed dramatically since ancient times when astronomers mistook the lights they saw in the sky for wandering stars. We've come a long way since then, but there's still much we don't know.

Could there be life on Mars? How many planets exist outside the solar system? Is there another "Earth" out there? And why can't we call Pluto a planet anymore? Discover the answers to these questions and more in this authoritative, essential guide to planets in the solar system and beyond.