Seemingly, not all celestial rocks succeed to form planets during the establishment of the our huge solar system. Some of them, with irregular shapes, just revolve around sun. They are what we call asteroids. These rocks contain silicon, chromium, calcium, and nickel. Some of those also contain gold and platinum.
A belt of asteroids is found between the orbits of Jupiter and Mars. The number of asteroids in the belt is around 1 lac which is equal with 0.1 million in other words. Each of it has different orbit, but only about 4000 of them are known.
The first asteroid discovered is called Ceres. With the diameter of about 1000 km, it is also the largest asteroid ever known. Another asteroid that has been discovered long time ago is Vesta. Discovered in 1807 AD, t this luminous asteroid has diameter of about 400 km.
As asteroids have various orbits, sometimes they crash each other and broken down completely. The rubble then sometimes enters the atmosphere of the earth and gets burn out because of the atmospheric friction. That is what we call meteor. Quite big meteors can reach the surface of the earth, which is called meteorites.
