In the vast, dark universe shine many galaxies that contain more than 1 billion stars. One small, ordinary star, the sun, has a special family of nine planets and moons called the solar system. The most unique planet in the solar system is the Earth, where life is able to exist. Nothing can live on the other eight planets: you would freeze on Pluto, fry on Mercury, and be squashed on Venus. Read all about the planets and about comets, asteroids, and meteors, and learn about spacecraft explorers.