BIRTH OF A SOLAR SYSTEM:

A planetary system is born from the gas and dust remaining after the formation of a protostar. The first stage is the building up of countless rocky lumps called planetoids by the accretion of grains of dust. In further collision, the planetoids break down and reform finally forming a small number of protoplanets. Nuclear reactions begin in the star while its radiation blows away the remnants of the cloud. Light gases like hydrogen, helium, methane and ammonia cannot be held by small protoplanets in the hotter inner regions of the system, but are retained as deep atmospheres around the larger, colder bodies farther out.

OUR SOLAR SYSTEM:

The Solar system or rather the family of the Sun consists of the Sun and nine planets,together with countless asteroids, moons, comets, meteoric particles on so on. Most of the material moves in orbits confined to a single plane but Pluto and some comets are notable exceptions.
The word planet has been derived from the Greek word 'Planete' which means 'Wanderer'.Astronomers of the ancient world knew only five planets-Mercury, Venus, Mars, Jupiter and Saturn as these planets could be seen with the naked eye from the Earth. Other planets were discovered only after the invention of the telescope-Uranus(1781) ,Neptune(1846) and Pluto(1930).(Image: Planets Alignment, Source:Unknown)

ASTEROIDS:

Apart from the nine planets, there exists a group of minor planets called Asteroids.These mainly lie in between the orbits of Mars and Jupiter. Asteroids vary in dimensions from a few hundred kilometers to just a few centimeters.The first of these planets were discovered in the year 1801 by the Italian Astronomer Giuseppe Piazzi and it was named Ceres.
Today however about five lakh asteroids have been found ranging in sizes from a few miles to about a few centimeters.It is now being predicted that there lies a huge pool of Comets beyond the orbit of Pluto which is refered to as Oort's Cloud.

DO OTHER SOLAR SYSTEMS EXIST?

A system of planets in the making may be revealed in the picture taken at infrared wavelengths by the IRAS Satellite.A disc of gas and dust is seen almost edge-on reaching 1000 billion km from the Star Beta Pictoris, the light which is blocked out by a dark mask at the centre.However later mathematical analysis have shown that such a senario would not give rise to a Solar System such as ours. Evidence indicating the existence of planets around other Solar Systems have come from work done at the Sproul Observatory in Pennsylvania.
A wobble in the movement of Barnard's Star, one of the Sun's closest neighbours,suggests the presence of invisible companions. Barnard's star is a red dwarf, about six light years from the Earth.There is a great deal of evidence for the existence of other Solar Systems however the probability of finding life on any one of them is very low.