Planets

How many planets are there in our solar system?

Earth is just one planet in our solar system. In our solar system there are eight planets and three dwarf planets: Ceres, Pluto and Eris. In order of distance from sun, the eight planets are: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. A good way to remember the order of the planets is to remember the sentence 'My Very Eager Mother Just Served Up Noodles'.

How were the planets created?

The solar system started as a massive, swirling dust cloud. About 5000 million years ago, the dust cloud began to shrink. As it shrank, gravity pulled most of the dust towards the centre of the cloud. Gas collected in the centre and heated up to become the sun. Leftover gas and dust in the cloud became the planets.

What are planets made of?

Some planets are made of gas. These planets are Jupiter, Saturn, Uranus and Neptune. Other planets are made of rock. They are Mercury, Venus, Mars and our own planet, Earth. One tiny little planet is not made of either gas or rock. Pluto is a dwarf planet right at the edge of the solar system. It is not considered to have an equivalent status to the other eight planets and so it is known as a dwarf planet. Pluto is made of frozen gases (ice).

The Planets - Further Reading

What is the movement of the planets in space?

The planets are positioned around a massive star called the sun. Each planet travels around the sun at various distances. Generally, the closer that a planet is to the sun, the faster it moves. This movement around the sun is called its orbit.

As well as orbiting the sun, each planet also spins around its own axis. This spinning speed is also different for each planet. As the planets spin on their own axis and orbit the sun, many planets also have natural satellites or moons which circle them. All this movement is what causes conditions such as light and darkness. This is how we measure days, months and years. It also determines the changing conditions of the seasons on Earth.

The Pluto controversy

When Pluto was discovered in 1930 by American astronomer Clyde Tombaugh, it was considered to be the ninth planet in the solar system. In 2006, however, astronomers decided to create a specific definition of what makes a planet. As a result, Pluto was re-classified as a dwarf planet.  For more information, see Topic 5, Chapter 4.