What is the probability of  comet hitting the earth?

Most planets in the solar system with a visible solid surface have craters. On Earth there are very few because geological processes such as weathering soon destroys the obvious evidence. On bodies with no atmosphere, such as Mercury or the Moon, craters are everywhere.There is strong evidence of a period of intense cratering in the solar system that ended almost 4 billion years ago. Since that time cratering appears to have continued at a much slower  rate. The cause of the craters is impacts by comets and asteroids. Most asteroids follow circular orbits between the planets Mars and Jupiter, but all of these asteroids are perturbed, occasionally by each other and more regularly and dramatically by Jupiter. As a result some find themselves in orbits that cross that of Mars or even Earth. Comets on the other hand follow orbits that often come close to Earth or other major bodies to begin with. These orbits are greatly affected if they come anywhere near Jupiter. Over the eons every moon and planet finds itself in the wrong place in its orbit at the wrong time and suffers the insult of a major impact.

Every day thousands of tiny pebbles and grains of sand pelt the earth. but the earths atmosphere protects us from anything bigger.

Here is a clip of a commit hitting the earth from a movie called deep impact...

Here is a more true to life version of a commit hitting the earth



BY ISABELLA GREEN (: