The solar system is a star system located in the Milky Way galaxy. There are billions of other solar systems in the galaxy. Our solar system consists of a star (the sun) and several planets. There are eight main planets and several dwarf planets. Planet Earth is one of the planets orbiting the sun.

Solar system (image: NASA).

Image: the sun and planets of the solar system. Earth is the third planet from the sun (Creative Commons: NASA).

Birth of the Solar System

How was the solar system created?

In the beginning, the universe consisted of huge clouds of gas and dust. Such clouds are known as nebulae. Even though the gas and dust were tiny particles, they all had the force of gravity. Gravity is a force of attraction between objects.

Over time, gravity began to pull the gas and dust together. About 4.6 billion years ago a nebula began to collapse. The collapse was caused by gravitational attraction. The nebula began to condense into smaller balls of dust and gas.

Gravity caused these balls to continue to shrink. The shrinking balls began to spin faster and faster. This created heat and the balls began to turn into stars.

Usually, a disc of gas and dust remained around each star.  Smaller balls of gas and dust began to form within this disc. These smaller balls began to turn into planets.

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The Sun

Our sun is the star located at the center of the solar system. It is made up of hydrogen and helium. As the sun was formed, it became hot and dense. Today, it continues to generate heat and light through nuclear fusion. The sun is considered a middle-aged yellow dwarf star.

The sun is the primary source of energy for life on earth. It is also the source of energy that drives the climate and ocean currents.

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The Planets in the Solar System

A planet is an object that orbits the sun, has sufficient mass to be round, is not a moon, and has removed small objects from the area of its orbit

There are eight main planets in the solar system. The four inner planets are the terrestrial planets. The four outer planets are giants.

Mercury, Venus, Earth, and Mars are terrestrial planets. They are located closest to the sun. They have a rocky composition and have a high density. In general, these planets have a solid surface and few moons.

Jupiter, Saturn, Neptune, and Uranus are the giant planets. They are located furthest from the sun. These planets do not have a solid surface. They are mostly made up of the gases hydrogen and helium. They are giant planets, but their gaseous nature results in low densities. They tend to have many moons. Sometimes they have planetary rings.

There are also dwarf planets that are too small to be considered a planet. Pluto and Ceres are the most well known of these dwarf planets.

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Other Bodies in the Solar System

In addition to the sun and planets, there are many other bodies in the solar system. These are some of the more significant ones.

Moons: are natural satellites that orbit most planets. Mercury has no moons, the Earth has one, and Saturn has over 60 moons. There are several explanations for how these moons came to be.  Some may have formed from the left over nebular material that created a planet. Others may be passing asteroids captured by the planet’s gravitational field. The earth’s moon is thought to have been created by the collision of an asteroid with the earth.

Asteroids: are rocky bodies that travel around the sun. Most are concentrated in a belt of asteroids between Mars and Jupiter. This asteroid belt may have been created by the break-up of a planet.

Meteoroids: are small rocky bodies. When they enter the earth’s atmosphere they become a meteor. Most meteors burn up in the atmosphere. A handful of meteors are large enough to reach the planet’s surface. These are meteorites. When a large meteor strikes the earth, large craters are created. It is thought that these can cause the extinction events that wipe out life on the planet.

Comets: are icy bodies that orbit the sun in an elliptical path. As they approach the sun, they begin to glow and develop bright tails.

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Vocabulary Building

The following is a recommended list of words and their definitions for students.

gravity: is the force of attraction between objects.

nebula: is a cloud of gas and dust in space.

planet: is an object that orbits the sun, has sufficient mass to be round, is not a moon, and has removed small objects from the area of its orbit.

solar system: is a star and the objects in orbit around it.

Improving Your Reading and Thinking Skills

Think for a few moments. Try to recall the major ideas in this article. Try to answer the following questions to improve your reading comprehension.

• What is a solar system?

• How was the solar system created?

• What are the types of planets found in our solar system?


The Origin, History, Evolution & Future of the Universe


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