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What is an asteroid?

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Quick answer

An asteroid is a rocky leftover from the early solar system, too small to be a planet. Most orbit the Sun in a belt between Mars and Jupiter, ranging from tiny boulders to bodies hundreds of kilometers across. It's a rocky or metallic object orbiting the Sun.

Key things to understand

  1. It's a rocky or metallic object orbiting the Sun.
  2. Most lie in the asteroid belt between Mars and Jupiter.
  3. They're leftovers from the solar system's formation.
  4. Sizes range from pebbles to hundreds of kilometers wide.
  5. A large impact is thought to have wiped out the dinosaurs.

People also ask

What's the difference between an asteroid and a comet?
Asteroids are rocky and mostly stay in the inner solar system; comets are icy, come from farther out, and grow tails near the Sun.
Where are most asteroids?
In the asteroid belt, a ring of rocky bodies orbiting the Sun between Mars and Jupiter.
Could an asteroid hit Earth?
Large impacts are rare but possible; agencies track near-Earth asteroids and study ways to deflect a dangerous one.

Part of the guide: Space & Astronomy →