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• The solar system is made up of the Sun (our nearest star) and the objects that orbit around it, including planets, asteroids and comets.
• Planets orbit the Sun in roughly circular paths, and moons orbit around planets.
• Asteroids and comets move in paths which are more oval in shape.
• The Sun’s gravity holds all of these objects together, and the gravitational forces between objects can cause less massive objects to orbit more massive objects.

Play this game to explore some key facts and figures about the solar system.

The term solar system means the Sun and all the objects that orbit around it. This includes:

• eight planets
• many moons
• five dwarf planets
• asteroids
• comets
• gas
• dust

At the centre of the solar system is the Sun – our nearest star. The Sun is a medium-sized star and is far closer to Earth than other stars. This is why it appears much larger and brighter than other stars. If the Sun were as far away as Proxima Centauri the next nearest star, it would be too small and dim to see.

The Sun contains most of the mass in our solar system. Although the Sun is not particularly large for a star (an equatorial circumference 4.3 million km across), it is very big and very massive compared to the planets.

The Sun’s enormous mass creates a strong gravitational field around it, which causes smaller objects like planets, asteroids and comets to orbit around it in elliptical paths. Planets orbit in roughly circular paths around the Sun, whereas asteroids and comets follow paths which are more oval in shape.

The four planets that orbit closest to the Sun are:

• Mercury
• Venus
• Earth
• Mars

These planets are known as terrestrial planets and are made mostly of rock and metal. The word terrestrial means ‘earth-like’, and these planets all have solid surfaces.

Most terrestrial planets have atmospheres, but the conditions on their surfaces would not allow humans to survive there.

Venus is the hottest planet in our solar system (despite being further from the Sun than Mercury), due to the high levels of greenhouse gases in its atmosphere. It has a surface temperature of over 470°C.

Only two of the terrestrial planets have moons orbiting them:

• Earth has one moon
• Mars has two moons – Phobos and Deimos

There are four more planets much further from the Sun:

• Jupiter
• Saturn
• Uranus
• Neptune

These planets are called the gas giants and they are very massive, and many times larger than the terrestrial planets. They are made of mostly hydrogen and helium gas, and they are all surrounded by rings and moons.

Jupiter is the largest planet in the solar system and has 79 moons. The four largest moons of Jupiter (Io, Europa, Ganymede, and Callisto) can be seen from Earth with just a pair of binoculars.

Saturn is almost as large as Jupiter and has 82 moons. It has a system of rings orbiting around it, which are made up of rock and icy debris.

It can be difficult to visualise the comparative sizes of all the planets in the solar system, so we have used different sized fruits and vegetables to help you. If Earth was the size of a cherry tomato, what size would the other planets be? Click or tap the image below to find out!

Between the orbits of the terrestrial planets and the gas giants, there are millions of asteroids – rocky objects that orbit the Sun and vary in size from 1km to around 1000km.

Most of the asteroids in the solar system are found between the orbits of Mars and Jupiter, in a region called the asteroid belt .

Like planets, asteroids are mostly made of rock and metal and they orbit the Sun, but asteroids are much smaller than planets so are also known as 'minor planets'.

As well as planets and moons, the solar system also contains dwarf planets, which are too small to be considered planets. The best known of these is Pluto, an ice dwarf that orbits far from the Sun, beyond the orbits of Uranus and Neptune.

Pluto was previously classed as the ninth planet from 1930 to 2006, until more dwarf planets were discovered and it was reclassified.

There are many comets in the outer solar system. Comets are icy objects, which orbit the sun at very large distances.

Comets orbit in paths which are highly elliptical and occasionally make their way into the inner solar system, where the Sun’s intense heat starts to melt them. This produces a large tail made of gases and dust, which can be many millions of miles long which reflects lots of the Sun’s light, causing them to glow brightly.

All objects exert gravitational forces on each other, causing them to be attracted together.

These forces can become very large when the objects have a high mass, like stars, planets or moons. As well as holding planets and asteroids in orbit around the Sun, these gravitational forces hold moons and satellites in orbit around planets.

To understand how gravity can cause an object to stay in orbit, it is useful to look at Isaac Newton’s thought experiment Newton’s cannonball.

In addition to planets and moons, many artificial satellites orbit around the Sun and the planets.

These are objects or machines that have intentionally been launched into orbit.

Artificial satellites have many uses, including: navigation, observing Earth, monitoring weather, space telescopes, and relaying communications signals. Some satellites, like the International Space Station, even carry humans.

Space probes are sometimes sent to explore further into outer space. These are robotic spacecraft which often fly past, or land on, other planets and moons – or even travel much further, away from our solar system.

Space probes have been sent to observe the outer solar system, sample the Sun’s atmosphere and even to visit a comet.