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Moon

A body orbiting a planet is called a satellite.

The Moon is a natural satellite that orbits planet Earth.

Many planets have moons, and some planets have many moons - Saturn has more than 50.

The Earth has just one moon - the Moon.

Dwarf planets

Pluto is a dwarf planet.

As the name suggests, a dwarf planet is smaller than a planet.

Its force of gravity is not strong enough to pull in all the many other objects in its orbit around the Sun.

Pluto is not very big.

It is only half as wide as the USA and is smaller than our moon.

The solar system contains hundreds of dwarf planets, including Ceres, which can be found in the asteroid belt.

Asteroids

Asteroids are made of metals and rocky material.

There are many asteroids in our solar system which orbit the Sun in oval or egg-shaped elliptical orbits which can take millions of years to complete.

There are large numbers of asteroids orbiting the Sun in the asteroid belt between Mars and Jupiter.

There are also many in a region beyond Neptune called the Kuiper Belt.

Comets

The solar system also contains small objects called comets.

Comets are similar to asteroids, but are made of ice, dust and rocky material.

As a comet approaches the Sun, it begins to vaporise, which means that it turns into a gas.

It then produces a distinctive tail, which lets us see it in the night sky.

The main difference between asteroids and comets is what they are made of.

• Asteroids are made up of metals and rocky material.
• Comets are made up of ice, dust and rocky material.
• Both asteroids and comets were formed early in the history of the solar system about 4.5 billion years ago.
• Both asteroids and comets orbit the Sun.

One way of remembering that a comet is made of ice is to highlight the letter c in both words

Summary

• The Sun, the eight planets, the moons, asteroids and comets make up our solar system.
• The order of the eight planets from the sun outwards is: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune.
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• The four inner planets are small, solid, rocky, dense planets, close to the Sun.
• The four outer planets are large balls of gas with a small, solid core, much further from the Sun.
• Asteroids are made up of metals and rocky material.
• Comets are made up of ice, dust and rocky material.