6.4. Asteroids

Asteroids are very small planets of rock and metal which revolve round the sun mainly between the orbits of mars and Jupiter. Actually, asteroids are a belt of a kind of debris, which somehow failed to assemble into a planet and keep revolving between the orbits of mars and Jupiter. There may be as many as 100,000 asteroids. The biggest asteroid called ‘ceres’ has a diameter of about 800 kilometres whereas the smallest asteroid is as small as pebble. Some experts believe that asteroids are the pieces of a planet that went close to Jupiter and was broken up by its gravitational pull. Others think that they are part of a ring of separate pieces of matter formed at the same time as the planets.

Sometimes an asteroid can collide with earth. Though the collision of an asteroid with the earth happens very rarely, even then a careful watch is kept on the motion of asteroids by the astronomers. This is because the collision of an asteroid with the earth can cause a lot of damage to life and property on the earth. In fact, the extinction of dinosaurs the earth which occurred about 65 million years ago, is believed to have been caused by the collisions of some asteroids with the earth.

When an asteroid collides with the earth, then a huge crater is formed on the surface of the earth. Many such collisions of the asteroids must have occurred in the past during the entire history of the earth which may have caused craters of different sizes on its surface. However, the natural process of soil erosion like wind and rain, tend to fill up these craters in due course of time. Only a few such craters survived on the surface of the earth so far. The ‘Lonar Lake’ in Maharashtra is one such crater formed by the collision of an asteroid with the earth.