Inner and Outer Planets | Internal and External Planets

Inner and Outer Planets

“Inner Solar System” and “Outer Solar System” are two subdivisions of the Solar System. The planets in our solar system are classified as inner and outer planets. Understanding the difference between inner and outer planets is fundamental to understanding the various properties of celestial bodies in our solar system.

Inner planets are defined as the four planets closest to the Sun: Mercury, Venus, Earth, and Mars.

Regarding the outer planets, there are the following four: Jupiter, Saturn, Uranus and Neptune.

Difference between Inner and Outer Planets

The inner planets, which are closest to the Sun, are solid rock balls and include Mercury, Venus, Earth and Mars. The inner planets were constantly bombarded by asteroids and meteorites for the first 600 million years of their existence. As a result, you will find craters of various sizes on the inner planets and their satellites.

The outer planets are large gaseous spheres with rings and include Jupiter, Saturn, Uranus, and Neptune. Between the inner and outer planets there is an asteroid belt.

Internal Planets

Internal planets, also known as terrestrial planets, are the ones in our solar system that are closest to the Sun. There are four of them: Mercury, Venus, Earth, and Mars. These planets are called “terrestrial” because they are solid and rocky, just like Earth.


It is the first planet in the solar system. Its close proximity to the sun means that it circles it twice in a single day. It takes its name from the Roman god of commerce and travel, Mercury. Also messenger of the gods, he was renowned for his high speed. This is probably why the Romans named the planet so when it was discovered.

Its ground is made up entirely of craters, a bit like on the Moon. Entirely burnt by the sun, there are only rocks and dust. Plains mingle with cliffs that are several kilometers long and can extend for hundreds of kilometers.

The temperature varies between 400 °C and -200°C (752 °F and -328 °F) depending on whether the face is exposed to the Sun or not.

At its heart, Mercury is made up of iron.


Venus is the second planet in the solar system. It closely resembles our planet, Earth.

A year on Venus represents 225 days.

Its atmosphere is made up of 95% carbon dioxide for 5% nitrogen. Strong winds of more than 300 km / h reign there at the top of the clouds. There are also very dense clouds of sulfuric acid responsible for a significant greenhouse effect that can push the surface temperature to 740 K, or 466 ° C.
These clouds also make it difficult to observe the surface of the planet when you are in orbit above it.

Its speed of rotation being too slow, Venus does not have a magnetic field.

The brightest after the Sun and the Moon, it is called the Shepherd’s Star when seen from Earth. This is how she got the name of Venus, goddess of beauty in Roman mythology. Indeed, it is considered the most beautiful planet visible in the sky.

Its soil is made up of lava and many erupting volcanoes.


Earth is the third planet in the Solar System. It circles the Sun in 365 days. It is so far the only planet on which life is possible.

Its atmosphere is 75% nitrogen and 21% oxygen.

It has a magnetic field initiated by electric currents from its steel core.

It has a satellite, the Moon, which influences its tides.


Mars is the fourth planet in the Solar System. It circles the Sun in 686 days.

The planet Mars takes its name from the Roman god of war. From Earth, this planet appears red and this is how humans since prehistoric times have associated it with the red color of the blood of battlefields.

Its atmosphere is composed of carbon dioxide, nitrogen and argon.

There are rocks and some craters on its soil. Plains mingle with volcanoes which can sometimes reach 200 km in radius and 20 km in height.

The climate on the surface of Mars is very heterogeneous. It can range from – 133 ° C to 70 ° C.

We know thanks to the photographs of its surface that water flowed one day on Mars. The latter left visible beds.

Mars is the source of superstitions about extra terrestrial life. Indeed, one has long with the existence of another form of life which would have been characterized by the Martians.

We know of two satellites to Mars: Phobos and Deïmos.

Earth Magnetic Field | Nicknamed “earth shield” by Scientists

External Planets

External planets, also known as gas giants, are the planets in our solar system that are farther away from the Sun compared to the internal planets. There are two external planets: Jupiter and Saturn.


Jupiter is the fifth planet in the Solar System. It is also the biggest.

It takes 11 years to circle the sun while it spins around every 10 hours.

It is a gas planet. This means that it has no solid surface. It is only made up of clouds. Its atmosphere covers 90% hydrogen for 10% helium. You can also find traces of water, ammonia or methane.
Its heart is very hot and is around 20,000 K, or about 19,726 ° C.

It also has a strong magnetic field that extends beyond Saturn.

Jupiter has been visited by many probes such as:

Pioneer 10;
Pioneer 11;
Voyager 1;
Voyager 2;
It is surrounded by almost 80 satellites. Like its neighbor Saturn, it is surrounded by quite small rings made of dust.


Saturn is the sixth planet in the solar system. It is also the second in size.

It takes Saturn approximately 29.5 years to complete its full orbit around the sun

Its atmosphere is much the same as that of Jupiter: 75% hydrogen and 25% helium.

Its core is made of silicates and iron. There is a temperature of 12,000 K.

Saturn is famous for its gas and dusty rings that revolve around it.

62 satellites revolve around it. The latter are of heterogeneous sizes. Sometimes as big as a planet and sometimes just small rocky clusters.


Uranus is the seventh planet in the Solar System.

It circled the sun in 84 years.

Invisible to the naked eye, it was the first planet in the Solar System to be discovered in 1781.

It is made up of rocks and ice and its atmosphere is made up of 83% hydrogen for 13% helium. The rest is methane, which gives the planet its blue color.

Its core is composed of silicates and iron surrounded by ice.

It rubs off 27 satellites and 13 rings.


Neptune is the eighth planet in the Solar System.

It takes 165 years to turn around the sun and 16 hours to complete a full turn.

The planet is made up of 15% hydrogen, ice, rocks and helium. Healing atmosphere is also composed of hydrogen and helium.

There are 14 satellites in Neptune.

Sources: PinterPandaiUniverse Today

Photo credit: Wikimedia Commons

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