Comparison Of Terrestrial Planets Biology Essay



The planets in our solar system is categorized in two parts, terrestrial the inner planets and Jovian the outer planets. Terrestrial planets are four planets which are closest to the sun, such as Mercury, Venus, Earth and Mars. According to their shapes and structure the terrestrial planets also known as rocky planets and they have roughly the same structure and shape, as a result these planets can be simplified to a central metallic core and an outer silicate rock mantle. In addition to these four planets, some of the satellites in the solar system can also be categorized as terrestrial.

In this picture it shows the terrestrial planets which are the first four closest to the sun and Jovian.

Picture Source: [Image] (accessed September 24, 2009)

General structure of terrestrial planets

Most terrestrial planets have a common structure, a central core and a surrounding mantle. the core is mainly compromised of iron, nickel and other heavy metals, it also may include other materials such as sulphur and silicon. The core itself can be divided into layers which may be molten or solid in state. The mantle which surrounds the core is mainly composed of silicate rocks, it also contains a large amount of minerals and metals. Again the mantle itself can be layered with the density of minerals increasing towards the centre, this however can be vary from planets to planet.

(The Terrestrial Planets, 2009)

Size comparison of terrestrial planets

Terrestrial planets Mercury, Venus, Earth and Mars ( from left to right ) this picture below clarifies the sizes of these four planets. Earth is almost the same size of Venus and sizes of Mercury is close to the size of Mars.


Size comparison between Terrestrial planets and Jovian

In this picture it clarifies the size comparison of Terrestrial and Jovial planets.



Picture source [Image] (accessed September 25, 2009)

Internal structure of the terrestrial planets

Despite the fact that terrestrial planets have similar structures, but the ratio of internal layers is not the same. Venus and Earth are very similar in size and the core size is also similar in both planets. If we compare the core of Mercury and Mars, Mercury has a much larger core than Mars and in overall size Mercury has smaller size compare to Mars.


Structure of Earth

The interior structure of the earth is the same as the other terrestrial planets, it is consisting of different layers, such as crust, mantle and core and these three layers are the main layers of the earth. The first layer is the crust which is the outer part and the second layer which is the middle layer is the mantle and the last layer is the core layer which is the inner layer.


The crust is a thin region and is mainly composed of low density silicates, the density however varies, and in some places the crust has much denser iron.

"The crust ranges from 5 to 70 km in depth and is the outermost layer. The thin parts are the oceanic crust which underlie the ocean basins, and are composed of dense iron magnesium silicate rocks. The thicker crust is continental crust, which is less dense and composed of sodium, potassium and aluminum. Silicate rocks, like granite. As the main mineral constituents of the continental mass are silica and alumina. The oceanic crust mainly consists of silica and magnesium. The crust-mantle boundary occurs as two physically different events. First, there is a discontinuity in the seismic velocity"

(Structure of earth, 2009)


Mantle of earth is about 2900 km, and it is the thickest layer of the earth. The mantle can be divided into upper and lower regions, the upper contains lower density iron and the lower however is much denser due to the increased weight and compression. The lower part of the mantle flows less easily than does the upper mantle. The upper mantle has been found in eroded mountain belts and volcanic eruptions.

"The lower mantle is probably composed mainly of silicon, magnesium, and oxygen. It probably also contains some iron, calcium, and aluminium. Scientists make these deductions by assuming the Earth has a similar abundance and proportion of cosmic elements as found in the Sun and primitive meteorites"

(Earth structure, 2009)


The core is divided into two sections, the upper core and the inner core. The upper core is surprisingly liquid and consists of mainly iron. The inner core is however solid and contains a mixture of iron and nickel.

"The outer core is a hot, electrically conducting liquid (mainly Iron and Nickel). This conductive layer combines with Earth's rotation to create a dynamo effect that maintains a system of electrical currents creating the Earth's magnetic field. It is also responsible for the subtle jerking of Earth's rotation. This layer is not as dense as pure molten iron, which indicates the presence of lighter elements. Scientists suspect that about 10% of the layer is composed of sulphur and oxygen because these elements are abundant in the cosmos and dissolve readily in molten iron"

(Moorland school, 2009).

The inner core is made of solid iron and nickel and is unattached to the mantle, suspended in the molten outer core. it is believed to have solidified as a result of pressure-freezing which occurs to most liquids under extreme pressure.

Earths atmosphere

The atmosphere of earth is a layer of different gases which are surrounding the planet earth and retained due to earth's gravity. The atmosphere has many advantages for our home planet earth, earth's atmosphere absorbs ultraviolet radiations and it is very protective for life on earth.


Venus is the second closest planet to the sun, it is the brightest natural object in the night sky, except sun and moon. Venus reaches its maximum brightness shortly before sunrise or shortly after sunset and that is why it is often called morning or evening star.

Venus is one of the terrestrial planet, it is very similar to earth in gravity and size, and because of that sometimes it is called the sister of planet earth. High reflective layers of sulphuric acid cloud have covered Venus, and these clouds preventing the surface of the Venus from being seen from space in visible light. From all the planets in the terrestrial planets, Venus has the densest atmosphere, mostly consists of carbon dioxide.

(Venus, 2009)

With respect to Venus, the internal structure cannot be known for sure since this would require extensive sampling and analysis. There are however a number of known properties, the similarities between earth and Venus in size, gravity and density shows that there might be some sharing between the interior structure of earth and Venus, like a crust, mantle and core. The core is thought to be at least partially liquid. The size of the Venus is slightly smaller than the size of the earth, therefore it suggest that it might have lower pressure in its deep interior than earth.

Compared to Earth, Venus is 5% smaller in diameter, the surface gravity is %10 less, the mass is 20% less and the internal pressure is known to be 20% lower. Therefore it is estimated that Venus has a density equal to 95% of Earth's density. As a result, Venus is known to have a structure very similar to Earth.



Mercury is an interesting planet, its internal structure is different from both Earth and Venus. it is the smallest planet in the solar system. However it has a very high density, 70% of Mercury is metallic and the rest of the planet is made of silicate material. The iron content is Mercury is the highest in the solar system.

The high density also suggests that the planet must have a much larger core compared to its size, possibly rich in the iron. This is estimated to be around 40% of its total volume. This is much bigger compared to Earth's core ratio

"Mercury is the second densest major body in the solar system after Planet Earth and its density is slightly less than the Earths. Mercury's smaller mass makes its force of gravity only about a third as strong as that of the Earth. An object that weighs 100 pounds on the Earth would weigh only about 38 pounds on Mercury."

(Facts about planet Mercury, 2009)

Mercury has a very thin atmosphere and it is because of the heat of the planet, therefore it has a weak atmosphere which contains hydrogen, helium, oxygen, sodium, calcium and potassium.

Picture Source: [Image] (accessed September 25, 2009)


The red planet is the fourth of the Terrestrial planets, it is also the second nearest planet to the Earth, and it might be the first planet visited by human. It has half the radius of Earth and has only 15% of its mass. It is also 20% less dense than Earth and as a result it has a much smaller core percentage, mars having a thin atmosphere are a terrestrial planet.

Mars is 59 million km away from earth, and it is the nearest planet to the earth which can be seen with fully details with a telescope. Olympus Mons is a huge volcano which is the highest point known in the surface of Mars.

(Mars, the red planet, 2009)

There are some similarities between Mars and earth, the interior structure of Mars suggests that it modelled with a thin crust like earth, mantel and core.

(Mars introduction, 2009)

Picture source [Image] (accessed September 25, 2009)


The planets in our solar system are divided into two parts, the inner and outer planets, the inner planets are Terrestrial Planets and the outer planets are called Jovian.

There are four Terrestrial planets which are closest to the sun, such as, Mercury, Venus, Earth and Mars. Terrestrial planets also called rocky planets due to lots of similarities to their shapes and structure with central metallic core and outer silicate rock mantle. In general the Terrestrial planets have common structure but different in sizes, that Earth is almost the same size as Venus and Mercury is close to Mars according to the size.

Earth has several distinct layers with their own different properties, such as, crust, mantle and core which are the main layers of the earth. Crust is the outer layer, mantle is the middle layer and core is the inner layer.

Venus is the second closest planet to the sun. Except sun and moon, Venus is the brightest object in the night sky, which reaches its maximum brightness in the evening and morning. Venus is very similar to the Planet Earth in size and gravity and its dense atmosphere consists of carbon dioxide.

Mercury is the planet the its interior structure is different from both Earth and Venus. Mercury is the smallest planet in the Solar System with very high density and 70% of Mercury is metallic and the rest are silicate materials.

Mars is the fourth planet and often called as the red planet and also second nearest planet to the earth. There are some similarities between Mars and Earth with thin crust, mantle and core.

Referencing list

The Terrestrial Planets, 2009.

(accessed 26 September, 2009)

Moorland. 2009. Earth science: the structure of earth.

(accessed 26 September, 2009).

The Structure of Earth, 2009.

(accessed 26 September, 2009)

Venus, 2009.

(accessed 28 September, 2009)

Facts about planet Mercury, 2009.

(accessed 28 September, 2009)

Mars, the red planet, 2009.

(accessed 28 September, 2009)

Mars introduction, 2009.

(accessed 28 September, 2009)

Moorland, 2009. Earth structure. (accessed 28 September, 2009)

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