*Comets are mostly made of ice and are very old. As they travel close to the Sun, some of the ice melts off and becomes a gas, causing bits of dust and debris to trail behind the comet. Asteroids, comets, and meteors are chunks of rock, ice, and metal left over from the formation of our solar system 4.6 billion years ago. There are currently about 1.3 million known asteroids, and more than 3,800 known comets. A meteor is a space rock that enters Earth's atmosphere, creating a streak of light in the sky. During ancient times, people believed that the passing of a comet was an omen of doom. Most meteor showers come from comets, whose material is quite fragile. Small comet fragments generally won’t survive entry into our atmosphere.