The solar system comprises of a star and all the objects that travel around it- moons, planets, comets, asteroids, meteoroids etc. Solar systems can have more than one star called as binary star systems; with more than two stars they are known as multi-star systems.
Our Solar System is located in the outer spiral of the enormous Milky Way Galaxy. It includes our star (the sun) and everything else that orbits around it. This includes the planets with their natural satellites, smaller planets with their satellites, asteroids, comets and also countless particles of small debris.
There used to be nine planets in our solar system. The sequence of them was- Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune and Pluto. Recently, Pluto has been removed from the list.
Solar system was formed around 4.5 billion years ago out of a dense cloud full of interstellar gas and dust. Supernova (shockwave of an exploding star) made the cloud collapse, forming a solar nebula (swirling disk). The gravity pulled more of it in the centre, increasing the pressure in the core which made the hydrogen atoms to combine forming helium and also releasing a large amount of energy. This gave rise to the sun and also more than 99% of the matter.
Matter in the outer part of the disk clumped together, smashed into each other, forming larger objects. Few of them were big enough to be shaped into spheres- planets, moons and dwarf planets.
Some of the matter did not clump together and could never become a planer. Those remaining tid-bits became the comets, asteroids, meteoroids and also irregular moons.
The arrangement and orderly distribution of planets in our system owes to the way the solar system was formed. Nearest to the sun, only rock-solid material could withstand the intense heat which is the major reason why the first four planets (Mercury, Venus, Earth, Mars) are terrestrial is nature with rocky and solid structures.
On the other hand, ice, liquid and gaseous stuff settled in the outer regions, pulled by gravity and hence we find gas in Jupiter and Saturn and also ice in Uranus and Neptune.
In the 17th century, Galileo Galilei’s discovered the concept of a solar system in which the planets revolved around the Sun. He used the telescope to establish that. At that time, the theory was revolutionary and known as Copernican Heliocentric theory. It refuted the earlier claims of Earth being the center of universe.