A part of astronomy is the planetary science which concentrates on studying how the planets, moons, dwarf planets, comets, asteroids and other bodies that orbit the Sun are gathered together. The formulation and evolution of our Solar System has been studied for a long time by now, first by telescope and now via spacecrafts, and the scientists have come up with explanation how the planets were formulated. Nowadays, the scientists are still making new discoveries, but the core ideas are the ones explained further in the following part.
Planetary science has divided the Solar System into three parts: inner planets, the asteroid belt, the outer planets. The planets were born from the protoplanetary disk that surrounded our Sun a long time ago. Gravitational attraction, collision and accretion formed the disk into clusters of matter which are known as protoplanets. The solar wind and radiation pressure excluded the matter that was not firmly enough attached to those clusters and also some planets that did not have sufficient mass did not retain a gaseous atmosphere of their own and disappeared. The planets that still existed continued to expel more matter and survived a period of intense bombardment. A hypothesis has been risen that states that the Moon was also a protoplanet but due to the bombardment collided.
Planets differentiated after they had reached sufficient masses. These processes cause the planet to develop a stony or a metallic core which can be surrounded by an outer surface or a mantle. Furthermore, the core of the planet can have either solid or liquid regions and some planetary cores also have a magnetic field for protection against solar wind stripping.
The interior heat that comes from the planet is due to the collision that once created the body of the planet, radioactive materials or tidal heating. Planets that have atmosphere can have erosion due to wind and water.
