Planets of the Solar System

What is the Solar System?

Look up on a clear night and you will see hundreds of tiny lights. Most of those are stars, very far away. But a few brighter ones that do not twinkle are actually planets — and together with the Sun, they make up our Solar System.

The Solar System is the Sun and everything that travels around it. That includes eight planets, dozens of moons, millions of asteroids, and icy comets. The word "solar" comes from Sol, the Latin name for the Sun. Everything here belongs to the Sun's family.

What holds it all together? Gravity. The Sun is enormous — you could fit more than a million Earths inside it — and its gravity pulls on everything nearby, keeping each planet looping around it in a path called an orbit.

The order of the planets

Here are the eight planets in order, starting from the one closest to the Sun:

1. Mercury — the smallest planet and the closest to the Sun.
2. Venus — covered in thick yellow clouds; the hottest planet of all.
3. Earth — our home, the only planet we know of with life.
4. Mars — the "Red Planet", rusty and dusty.
5. Jupiter — the giant, with a huge storm called the Great Red Spot.
6. Saturn — famous for its beautiful rings of ice and rock.
7. Uranus — a pale blue-green planet that spins on its side.
8. Neptune — the most distant planet, deep blue and very windy.

A handy way to remember the order is the sentence: My Very Easy Method Just Speeds Up Naming. The first letter of each word matches the first letter of each planet.

Two kinds of planet

The planets split neatly into two groups.

The inner planets — Mercury, Venus, Earth and Mars — are small and made of rock. You could stand on their solid surfaces. They are sometimes called the "terrestrial" planets, which just means "earth-like".

The outer planets — Jupiter, Saturn, Uranus and Neptune — are giants made mostly of gas and ice. They have no solid ground to stand on. Jupiter and Saturn are called "gas giants"; Uranus and Neptune are colder and called "ice giants".

Between the two groups lies the asteroid belt, a ring of rocky lumps that never formed into a planet.

Why we have day, night and years

Each planet does two movements at the same time, and these explain how time works on Earth.

First, a planet spins on an invisible line through its middle called its axis, like a spinning top. Earth turns all the way around once every 24 hours. The half facing the Sun has daytime; the half turned away has night-time. So night is not the Sun switching off — it is your part of Earth turning to face away.

Second, a planet orbits the Sun. Earth takes about 365 days — one year — to travel all the way around. Planets closer to the Sun have shorter years, and faraway ones have much longer years. A year on Neptune lasts about 165 Earth years!

This is also why some planets are scorching and others are freezing. Mercury and Venus sit close to the Sun and bake, while Neptune is so far away that it is one of the coldest places in the Solar System.

Earth: the just-right planet

Of all eight planets, only Earth has liquid water, breathable air and gentle temperatures. It sits in just the right place — not too hot, not too cold. Scientists call this the "Goldilocks zone", because like the porridge in the story, the conditions are just right for life.

That is one reason looking after Earth matters so much. As far as we know, it is the only home life has.

Try it yourself: build a planet walk

The planets are not just different sizes — they are spread out over huge distances. You can feel this with a simple outdoor model.

1. Find a long, open space such as a park, playground or a quiet street.
2. Mark the Sun at one end with a ball or a chalk circle.
3. Now take steps to place each planet. A simple version: Mercury at 1 step, Venus at 2, Earth at 2½, Mars at 4, Jupiter at 13, Saturn at 24, Uranus at 49 and Neptune at 76 steps.
4. Walk it out as a group, with one person standing at each planet.

You will quickly notice the four rocky planets are bunched up near the Sun, while the giants are spread far, far apart. That empty space between them is what makes our Solar System so vast — and why spacecraft take years to reach the outer planets.

Want to keep exploring the sky? See The Sun, the Moon and the Stars for a gentle first look at space, and Climate and Weather to discover how the Sun shapes life right here on Earth.