Formation of Solar System

Our solar system was formed about 4.5 billion years ago from dense cloud of interstellar gas and dust.

Our solar nebula:

But what is a nebula? It's the collection of loose clouds of gas and dust, a spinning, swirling disk of material.

Possibly due to presence of shockwaves of a nearby supernova these gases collapsed and became more and more dense. In the upcoming million years the nebula contracted and cooled. Once the formation started it was irreversible to recreate nebula. Sun was formed surrounded with thin, swift disk of gas and dust similar to rings of Saturn today.

                  

Formation of The Sun:

The Sun is formed from the giant, rotating cloud of gas and dust. 

Gravity at the centre pulled more and more material in. The pressure in the heart was ultimately so high that hydrogen atoms started to fuse and form helium, releasing a massive amount of energy. With that, our Sun was born, and more than 99 percent of the available matter gradually accumulated.

Formation of Planets:

The Rocky Planets:

The inner or rocky planets are Mercury, Venus, Earth and Mars. As they were close to the young sun, here intensity of light and heat was huge. As a result ice evaporated and gases like Hydrogen and Helium simply blew away. Now, nothing other than rocks left which combined to form planets, dwarf planets, moons and the asteroid belt.

    Newly Formed Earth

Our Earth was struck to an object nearly to the size of mars and the debris from that became our moon.

The Gas Giants:

They include Jupiter, Saturn , Uranus and Neptune.

As they are far from the Sun here temperature was low allowing ices to survive which formed planetary cores in short amount of time. These large cores were able to hoover up any surrounding material like Hydrogen and Helium forming thick atmospheres.

Astronomers believe that Jupiter, Saturn, Uranus and Neptune, the four giant planets of our solar system, originally formed far closer together than they are today, and slight encounters with the remaining debris around them caused them to change their orbits.

One can say Jupiter and Saturn drifted towards the sun and Uranus and Neptune migrated gradually outwards.

That's how The Gas Giants were formed.