Free Astronomy Essay Sample


A solar system exists which is a central sun with various bodies such as meteors, asteroids, satellites, comets and planets. These planets are grouped into terrestrial planets and Jovian planets. This essay discusses various aspects of the terrestrial planets.

Get a Price Quote:
- +
Total price:

Terrestrial planets

A terrestrial planet is defined as any of the planets that are closer to the sun and are similar in composition and density. In the solar system, the terrestrial planets are four in number and they include Earth, Mars, Mercury and Venus. These four planets are also referred to as inner planets because they close to the sun. Other names for them are telluric planets and rocky planets (Universe Today). The terrestrial planets have the following common characteristics (WiseGEEK).

i.  They have very weak magnetic fields

ii.  They have orbits that are closely spaced

iii. They have no rings around them

iv. The either have few moons or no moon

v.  They are near the sun

vi.  They are composed of heavy metals and rocks

vii.  They have varied terrain such as mountains, craters and volcanoes.

Averagely, Mercury is about a third as far as Earth. This contributes to the very high temperatures of Mercury as compared to other terrestrial planets. The distance of is about 50% larger than the distance of the earth. The orbits of the Earth and Venus are almost perfectly circular whereas the orbits of mars and mercury are elliptical making their distances from the sun vary over time than Venus' and Earth's. The table below shows the average distances of the four terrestrial planets (The Planetary Society).






Average distance

57,900,000 km

108,200,000 km

149,600,000 km

227,900,000 km

Maximum distance/aphelion

69,800,000 km

108,900,000 km

152,100,000 km

249,200,000 km

Minimum distance/ perihelion

46,000,000 km

107,500,000 km

147,100,000 km

206,600,000 km

Fig1. A table of average distances of the terrestrial planets (The Planetary Society).

The average masses and density of the terrestrial planets are shown in the table below.



Terrestrial planet

Average mass

Density (gm/cm3)


















Fig2. A table of masses and density of terrestrial planets (Zubay, L. G, Pg 48).

The composition of terrestrial planets

Mercury:  this is the innermost solar system's planet. Its surface is composed of craters and the temperatures at the surface are very high because of its closeness to the hot sun. It is believed that the interior of Mercury is made of a molten core. The mercury's core covers about 42 percent of its volume and it is mode of molten iron (Universe Today).

Venus: The density of Venus in the above table suggests that it has a large iron core similar to other terrestrial planets in the solar system. By analogies with the earth, the Venus' core is believed to be partly liquid (Faure, G and Mensing, M. T, Pg 201). The components of the surface of Venus have not been studied due to the fact that the planet is shrouded in a very thick atmosphere that hides its surface.

Earth: the core of the earth is believed to be made of two main parts I.e. the inner core of radius 1220 kilometers and the outer core of radius 3400 kilometers. The Earth's core is made of 80 percent iron. Also, there are other elements such as nickel, platinum, uranium and gold. The inner core of the earth is solid while the outer core is liquid (Cain, F). The surface of the earth is composed of gases where the major ones are argon, oxygen and nitrogen (Egger, E. A).

Mars: The core of mars is composed of liquid iron and sulphides. The surface of Mars is covered with dust which is rich in iron. The surface is dry and rocky (MARS).

Characteristics used to determine whether a planet is terrestrial or jovial

All the terrestrial planets can be identified using their physical characteristics that are the same as those of the Earth. Are approximately of the same size and they are considerably denser relative to the Jovian planets. They planets can be determined through their poles. For instance, the terrestrial planets have less flattened poles as compared to the Jovian planets. Spin can be used to determine the planets. The spin of the terrestrial planets spin less rapidly as compared to that of the Jovian planets.

Similarities between terrestrial and Jovian planets

The following are some of the planets' similarities (Find Health, Education, Science & Technology Articles, Reviews, How-To and Tech Tips at Bright Hub)

i. They are all spherical in spherical shape

ii. These planets are characterized by several storms

iii. They both have an associated magnetic field whereby the fields are more stronger in the Jovian planets

iv. They both have gaseous atmospheres

v.  Even if the planets differ in structure, they both have solid core and the cores for terrestrial planets are larger than those of Jovian planets.

vi. They or form part of the same primordial solar nebula

vii. They all move around the sun in elliptical orbits with different eccentricities

Similarities between terrestrial planets and comets

The comets are bodies made up of dust and a mixture of ammonia, water and methane. They have a nucleus, head and gaseous tail. The main common feature between the comets and the terrestrial planets is that they all move around the sun whereby the comets move on an elongated orbit.

Similarities between terrestrial planets and Kuiper Belt Objects

Kuiper Belt Objects are huge groups of rock and ice that are found near the orbit of Pluto. The main common feature between the terrestrial planets and the Kuiper Belt Objects is that they both orbit around the sun (Windows to the Universe).


In our solar system, there are four terrestrial planets namely: Earth, Mars, Mercury and Venus. The cores of these planets mainly comprises of iron. Among the bodies in the solar system, the asteroids and the terrestrial planets do not have any feature in common. However, there are common features between the terrestrial planets and the Kuiper Belt Objects, comets and Jovian planets.


Have NO Inspiration
to write your essay?

Ask for Professional help