Comets

Comets are leftovers from the formation of the nine planets in the solar system billions of years ago. Comets are fragile balls of snow and dust found at the edge of the solar system in the Oort Cloud. The Oort Cloud is made up of about 10 million comets, some of which leave the cloud and travel toward the Sun. The Sun's heat melts the snow and these comets appear to grow greatly. Astronomers have seen about 700 comets in the Earth's sky.