Do you ever wonder how terrestrial planets came into being? Does their formation elude your perception? Though there is no definite theory as to how planets are formed, scientists have a particular presumption about the process of their creation. The theory states that planets form during the collapse of a nebula, into a thin disk of gas and dust. This disintegration of the nebula leads to the formation of a protostar at the center, which is surrounded by a rotating protoplanetary disk. Then, the process of sticky collision takes place and dust particles in the space mount-up the mass, to form large bodies.
While the local mass or planetesimals gets stuck to the large body, the gravitational pull of the body attracts more materials, present in the space, to it. The concentration of the bodies becomes denser and denser, until the moment comes when they collapse to form protoplanets. It is believed that once the planet reaches the size of the Earth's satellite i.e. moon, they begin accumulating an extended atmosphere, by means of atmospheric drag, which in turn increases the capture rate of the planetesimals.
Once the protostar grows to reach a particular size, it can light to form a star. It is at this stage that photoevaporation, the solar wind, Poynting-Robertson drag and other effects take place, removing the surviving disk from the inside. Subsequently, the protoplanets orbit the star or collide with each other, to form a large planet. They can also release materials, which would be attracted to the other protoplanets. Protoplanets that have absorbed a lot of mass would readily become a planet, while the rest, which have survived natural collision, would form natural satellites or dwarf planets or small bodies.
The interiors of a planet get heated up by the energetic impacts of the smaller planetesimals. This causes the planet to melt partly. Its insides then get denser in the core and starts varying in their mass. The effect is more prevalent in planets that are smaller in size, as they lose most of their atmospheres because of the accumulation. However, the loss in gases is restored by out gassing from the mantle and also from the successive impact of comets. There are various escape mechanisms through which smaller planets lose atmosphere they had gained.