How does accretion theory explain planetary formation?

Accretion theory explains planetary formation as a process where dust and gas particles in space gradually come together to form planets.

The accretion theory, also known as the nebular hypothesis, is a widely accepted model that explains the formation of planets and other celestial bodies. According to this theory, planets are formed from the dust and gas that surround a young star, known as a protostar. This dust and gas, collectively referred to as a protoplanetary disk, is the leftover material from the star's formation.

The process begins with the dust particles in the protoplanetary disk. These particles, due to their mutual gravitational attraction, start to collide and stick together, forming larger and larger clumps. This process is known as accretion. As these clumps grow in size, their gravitational pull also increases, attracting more and more particles and growing even larger. Over time, these clumps can grow to become planetesimals, the building blocks of planets.

The planetesimals continue to collide and merge, forming protoplanets. These protoplanets continue to accrete more material, growing in size until they become full-fledged planets. The process of accretion is not a quick one; it can take millions to billions of years for a planet to fully form.

The accretion theory also explains the different types of planets. Close to the star, where temperatures are high, lighter elements like hydrogen and helium are blown away by the star's radiation. This leaves behind heavier elements like iron and nickel, which form terrestrial planets like Earth. Further away from the star, where temperatures are lower, lighter elements can survive, leading to the formation of gas giants like Jupiter.

In summary, the accretion theory provides a comprehensive explanation of how planets form from the dust and gas surrounding a young star. It explains the process of accretion, where particles gradually come together to form larger and larger bodies, eventually leading to the formation of planets.