Asteroids are small, rocky celestial bodies. The most familiar group of asteroids to many is the Asteroid Belt, located between Mars and Jupiter. Most of these extraterrestrial rocks are small in size. However, extremely large ones have been noted, such as the asteroid Ceres, which is approximately 930 kilometers in diameter. There are two other main groups of asteroids in our solar system.
One of these groups is called the Near Earth Asteroids. These rocks, while orbiting the sun, often are in close proximity to the Earth and there have been some fears that possible collisions may occur, but so far nothing on any great scale has taken place in the past decade or so. So these asteroids rarely cause any disturbances or worry among people and the likelihood for an asteroid to impact the earth is very small. The other group is called the Trojan Asteroids. These pieces of rock and debris orbit Jupiter and are usually either a little ahead or a little behind the planet in its orbit.
There are so many different types of asteroids in our solar system that each one at first glance looks totally unique and different. Some asteroids are solid rock or metallic, while some can be just small pieces of rock slackly held together. Yet the reason why most asteroids look so unique is due to the number of collisions they have suffered. In high concentrations of asteroids, especially in the Asteroid Belt, the probability of one asteroid smashing or bumping into another is very high. Slowly but surely many of these rocks become disfigured, adding more debris to the universe. There are three types of objects which sometimes resemble asteroids. These are the meteor, meteorite, and meteoroid, each describing the phase of the objects life: moving in space, through the atmosphere, and having struck a surface, respectfully.