An asteroid is a chunk of rock and metal that orbits the Sun, often found in the vast space between Mars and Jupiter. Most asteroids are leftovers from when our solar system formed about 4.6 billion years ago: they're pieces that never came together to form a planet.

Asteroids range from the size of a pebble to hundreds of miles across. The largest in the asteroid belt, called Ceres, is about as wide as Texas. Unlike planets, asteroids have irregular, lumpy shapes because they're too small for gravity to pull them into spheres. When you see pictures of asteroids, they often look like giant potatoes floating in space.

Scientists study asteroids because they're like time capsules, preserving clues about the early solar system. Some asteroids occasionally cross Earth's orbit, which is why astronomers track them carefully. About 66 million years ago, a massive asteroid struck Earth, creating an explosion so powerful it contributed to the extinction of the dinosaurs.

When a small piece of an asteroid breaks off and enters Earth's atmosphere, it becomes a meteor, creating a bright streak across the night sky that people call a shooting star. If it survives the journey and lands on Earth, scientists call it a meteorite.