What are asteroids?

                We all know that in our solar system there are nine planets which always revolve round the sun in elliptical orbits. In addition to these planets, there are many small bodies or irregular lumps of rocks which orbit the sun. These small heavenly bodies are called ‘asteroids’ or ‘planetoids’.

               There are about 100,000 asteroids but majority of them are two small to be seen from the earth. Each asteroid has its own orbit in which it revolves round the sun. The biggest asteroid is ‘Ceres’. It measures 1/800th of the size of the earth. The Italian astronomer Piazzi discovered this asteroid in January 1801. The ‘Vestal’ is the only asteroid visible to the naked eye though it was discovered after “Ceres”. The diameter of these asteroids range from 1 km to 800 kms. The total mass of these asteroids is 1/3000th of that of the earth. Two-thirds of the asteroids revolve in orbits lying between the orbits of Mars and Jupiter. Some asteroids revolve between Mercury and Mars also. The asteroid ‘Incarus’ is one of them. The orbit of the asteroid named ‘Hidalgo’ lies between Mars and Saturn. The asteroids ‘Hermes’ and ‘Eros’ are within a range of a few million kms from the earth.

               Eros is a small asteroid that wanders from the asteroid belt and comes within a range of 25.6 million kms from the earth in every seven years, i.e. closer than any other body in the solar system except the moon. It was discovered by G.Witt, in 1898. A second asteroid belt beyond the orbit of “Pluto” has been assumed by the scientists in their recent studies.

               These bodies appear like saucers under powerful telescopes. Some of them are very bright, while some others are faint. Their sizes have been determined on the basis of their brightness.

               Most of the asteroids are constituted of the same ingredients of which the rocks on the earth are made. Their surface temperatures however differ. Scientists believe that asteroids might have originated when some big planets exploded in space and its small pieces then started revolving round the sun. However, nothing can be said about their origin correctly.