Space is a rocky place. The biggest space rocks are asteroids. As they bang around out there in space, these rocks break into smaller and smaller pieces that sometimes fall to Earth.
Most of them burn up in streaks of light. Some crash into our planet and leave behind meteorites. Every once and a while, a really big one makes a giant crater.
Smaller pieces of rock and iron that travel through space are called meteoroids. Meteoroids orbit our Sun just like asteroids and planets.
When a space rock enters a Earth's atmosphere, it becomes a meteor - or shooting star. The meteor heats up and makes the air around it glow. We see a streak of light. Most meteors burn up. Scientists think up to 10,000 tons of meteors fall on the Earth each day, but most are no bigger than a speck of dust.
A meteor makes it all the way to ground without burning up is called a meteorite. Meteorites range in size from tiny pebbles to boulders.
Some planets and moons don't have enough atmosphere to protect them against meteor and asteroid impacts. Earth's moon, Mercury and even Mars are covered with round impact craters from these collisions.