Asteroids are small rocky bodies that orbit the sun, located primarily between Mars and Jupiter. They range in size from dust particles to hundreds of kilometers in diameter. Most asteroids are composed of rock and metals. While in space they are called asteroids, on Earth they are known as meteoroids before entering the atmosphere and meteorites after landing. The vast majority of known asteroids orbit within a belt between Mars and Jupiter, though some have orbits that cross into the inner solar system. Over 300,000 asteroids have been identified so far.

1. Asteroids

2. DefinitionAsteroids, sometimes called minor planets or planetoids, are small Solar System bodies in orbit around the Sun, especially in the inner Solar System.

3. Asteroids are material left over from the formation of the solar system. One theory suggests that they are the remains of a planet that was destroyed in a massive collision long ago.

4. They are smaller than planets but larger than meteoroids.

5. The term "asteroid" has historically been applied primarily to bodies in the inner Solar System since the outer Solar System was poorly known when it came into common usage.

6. The distinction between asteroids and comets is made on visual appearance: Comets show a perceptible coma while asteroids do not.Brief HistoryThe first asteroid was discovered in 1801 by Giuseppe Piazzi of Italy.

7. He named it "Ceres" after the Roman goddess of grain.

8. Ceres is the largest known asteroid at approximately 950 km (590 miles) in diameter, and it lies in the belt of asteroids between Mars and Jupiter at an average distance from the sun of 2.6 A.U.

9. Ever since, asteroids have received an official designation of a number (starting with Ceres of number "1"), and most larger ones have received a name based in Roman mythology.

10. If they have a name, then they are usually referred to with the number then the name, such as 951 Gaspra.

11. Currently, asteroids are also referred to by the International Astronomical Union (the only official body that can name astronomical objects) as minor planets.SizeAsteroids vary greatly in size.

12. The largest and first known asteroid, Ceres, was discovered in 1801. It is 580 miles (933 kilometers) in diameter.