What are the four stages of a Terrestrial Planet?

Our solar system is full of mysteries. The biggest mystery is about its formation. There have been many theories put forward by great thinkers and philosophers, but according to the most popular theory of planetary formation, solar system coalesces from interstellar dust and rocks in four distinct phase. First one is the sudden gravitational collapse of a dislike cloud that surrounds the hot core. Second and third phases are the condensation of cloud and the combination of gas and dust particles into a solid object called planetesimals. The last phase is the compression of these planetesimals with dust and ice particles in a process known as runaway accretion.  Our solar system contains many planets out of which only eight are known. These planets are categorised into terrestrial planets and Jovian planets. Mercury, Venus, Mars, and Earth are terrestrial planets while Jupiter, Saturn, Uranus, and Neptune are jovian planets. The main difference between terrestrial and Jovian planets are regarding their size and satellites. Terrestrial planets are smaller in size and have less number of satellites as compared to Jovian planets.

Four stages of terrestrial planet


Terrestrial planets are formed through a process called accretion. It is a process in which the microscopic particles condensed together and further grow into planets.  These particles are held together by the electrostatic force of attraction. But as their size increases the gravitational force also increases, which further accelerate their growth. This results in the formation of planetesimals which further grow in size to form planets.



The first stage involved in the planetary development is Differentiation. It is quite a complicated process. Differentiation is the process of separating out the constituent particles from the planetary body depending on the density. The denser materials of a planet sink to the centre while the less dense materials rise to the surface. Denser materials migrate to the core whereas the lighter materials from the crust and atmosphere. Differentiation occurs as the system seeks to minimise the gravitational potential. There are two types of differentiation which are involved in the planetary development.

Stages of Planetary Formation

They are:

  1. CHEMICAL DIFFERENTIATION: – It describes the process in which the material separate out due to their difference in their densities. The heavier particles sink to the centre of the planet while the lighter particles rise and form the early atmosphere. The inner core is solid due to the presence of materials such as iron, nickel while the outer core is liquid.
  2. PHYSICAL DIFFERENTIATION: – It involves the following steps

GRAVITATIONAL SEPARATION: It is similar to that of chemical differentiation where the particles separate out due to the difference in their densities.

Moon’s KREEP: On the Moon, a distinctive basaltic material has been found which is high in incompatible elements such as phosphorus, rare earth metals, potassium which is denoted by the abbreviation KREEP.

Four stages of terrestrial planet

FRACTIONAL MELTING AND CRYSTALLIZATION: – Magma in the earth is formed by the partial melting of a source rock in the mantle. The melt extracts a large portion of the conflicting elements which are not stable when present in the major minerals. As the magma rises above a certain depth, the minerals present in it start crystallising at a particular temperature and pressure. This results in the formation of solids which removes elements from the melt.

THERMAL DIFFUSION: – When the material is unevenly heated the lighter particles move to outer zones while the heavier materials move to the colder zones. This process is known as thermophoresis or the Soret effect.

DIFFERENTIATION THROUGH COLLISION: – Differentiation on Earth had already separated the lighter and the heavier particles. The Moon’s density is considerably less than that of Earth, due to lack of the large iron core.

Four stages of terrestrial planet

  1. CRATERING: – The crust which is newly formed slowly cools down but the bombardment of planetesimals continues and the planet that is formed result in the formation of craters. A crater is a large bowl-shaped cavity in the ground or on a celestial object which is caused by the explosion or an impact with a meteorite. The Moon and Mercury’s surface has a large number of craters.
  2. FLOODING: – While catering was still occurring, the crust of a planet fractured, the lava evolved out and flew through the craters, smoothing and filling them. In the case of Earth water also flew through the craters during the planetary formation. It rose into the atmosphere and came back to the earth as rain resulting in the formation of many water bodies. However, this didn’t happen in other planets of the solar system. That is why we find only lava flooding in other planets.
  1. SURFACE EVOLUTION: – The last stage of planetary formation is Surface Evolution. It takes place about billions of years ago. The face of the planet got slowly altered by the movement of tectonic plates and the movements of air and water. The movement of the tectonic plates results in the formation of mountains. It also gave rise to shift In continents. Meanwhile, the wind took away all the unwanted materials from the surface.

Four stages of terrestrial planet


Q1. What is the difference between volcanism on Venus and that around the ring of fire on Earth?

The volcanoes nearby the ring of fire on earth are composite volcanoes. In this type of volcano, the oceanic crust of one plate is sliding underneath the subduction zone forming a gummy sort of lava.
The volcanoes on Venus are shield volcanoes which project magma from the depths above hot

Q2. What is the difference between terrestrial and Jovian planets?

The two most important aspects are regarding size and number of satellites. Terrestrial planets are smaller in size as compared to the jovian planet. Also, terrestrial planets have less number of satellites. Venus, Mercury Earth and Mars are terrestrial planets while Jupiter, Saturn, Uranus and Neptune are jovian planets.