Planets of our Solar System - BBC Bitesize (2024)

Our Solar System is amazing!

At the centre is the Sun. Orbiting around the Sun are eight planets with over 100 moons between them, at least five dwarf planets, countless asteroids and the occasional comet.

In this Space guide you can learn about:

• the role of the Sun in the Solar System
• the different types of planets: terrestrial, gas and ice
• the main features of the other planets
• how we explore space and learn about other stars and planets

In the centre of the Solar System is the Sun, our star. It is a huge ball of burning gas made mostly of hydrogen.

The Sun makes up 99% of all the mass in the Solar System; that means if you put together everything else in the Solar System, the Sun would be 99 times more massive!

Astronomers think the Sun is about 4.6 billion years old and it is about half way through its life.

The planets

Every object in our Solar System is held in place by the Sun’s gravitational pull.

The planets in the Solar System are all different but we can divide them into groups based on their common features.

• There are four planets (Mercury, Venus, Earth and Mars) which have solid, rocky surfaces.

• There are two gas giants (Jupiter and Saturn) which are made of gas and are the largest planets in the Solar System.

• There are two ice giants (Uranus and Neptune) which are so far from the Sun that they are frozen solid.

is a small rocky sphere, not much bigger than our Moon.

It is the closest planet to the Sun, about two fifths of the distance between the Sun and Earth. This means the side facing the Sun can get very hot - up to 430°C during the day.

But Mercury has almost no atmosphere, so it does not hold onto this heat. The side facing away from the Sun cools down to -180°C at night.

It takes Mercury 59 days to spin round once on its axis. Mercury travels very fast around a short orbit, so its year is only 88 days long.

is the second planet from the Sun - about three quarters of the distance between the Sun and Earth. It is known as Earth’s twin because they have very similar sizes.

Venus is the hottest planet in the Solar System with an average temperature of 460°C.

Its thick atmosphere acts like a blanket trapping the Sun’s heat inside.

The surface of Venus is dry and rocky with lava flows across parts of the planet.

It takes Venus 243 Earth days to spin round on its axis but only 225 days to complete an orbit of the Sun. So a day on Venus is actually longer than a year!

is the third planet from the Sun and the only planet in the Solar System with life on it.

Our planet is habitable because it is just the right temperature to support life.

Earth lies in the Goldilocks Zone where it is not so close to the Sun that it gets too hot and not so far from the Sun that it gets too cold.

It also has an ideal atmosphere, which traps just the right amount of the Sun’s heat to keep Earth's temperature stable.

Both these features contribute to Earth having liquid water on the surface, which living things need to survive.

is the fourth planet from the Sun and the last of the terrestrial planets. It is about half the size of Earth and about one and a half times the distance from the Sun that Earth is.

Like Earth, Mars is in the Goldilocks zone but its thin atmosphere does not trap enough of the Sun's heat to have a stable temperature. At its hottest, Mars reaches about 20 °C but this can drop to -153 °C. There is water on Mars but it is in the form of ice under the surface at the planet's poles.

Evidence from the Curiosity and Perseverence rovers on the surface of Mars shows that Mars used to have a thicker atmosphere and it once had liquid water on the surface, and therefore possibly life.

Mars has two moons. A day on Mars lasts just over 24 hours and a year lasts 687 Earth days.

Between Mars and Jupiter is the main .

Asteroids are rocky objects that orbit the Sun, just like planets do. There are millions of asteroids of very different shapes and sizes.

• Some are almost spheres, like planets, but most are irregular shapes.
• Some are the size of small stones and pebbles.
• Some measure hundreds of kilometres across.

The largest object is the asteroid belt is the dwarf planet Ceres, which is 950km in diameter (that's about the same the length as Great Britain).

is the fifth planet from the Sun and the largest planet in the Solar System.

It is about five times the distance from the Sun that Earth is and eleven times the width of Earth. Jupiter is so huge that it is twice as massive as all the other planets in the Solar System put together.

Jupiter's stripy appearance is caused by winds blowing clouds of different types of ice, liquid and gas around. The Great Red Spot on its surface is a huge storm that has been raging for at least 300 years.

Jupiter is thought to have 80 moons. The largest four are called Io, Europa, Ganymede and Callisto, They can be seen from Earth with a pair of binoculars or a telescope.

A day on Jupiter lasts less than ten hours and a year takes around twelve Earth years.

is the sixth planet from the Sun and the second gas giant.

It is about nine times the width of Earth and nine and a half time further away from the Sun.

Saturn is the least dense planet. Its density is so low that it would float on water – if you could find a bathtub big enough!

Saturn is famous for its beautiful rings which extend out about 280,000 km from the planet, the rings have an average thickness of only 10m.

The rings are thought to be bits of comets, asteroids, or moons that broke up before they reached the planet. As well as its rings, Saturn is orbited by 83 moons.

A day on Saturn lasts for just under eleven hours, while a year is about 29 Earth years.

is the seventh planet from the Sun and the first of the ice giants.

It is four times wider than Earth and nearly twenty times further from the Sun.

Because it is so far from the Sun, the average temperature on the surface is only - 195°C. The coldest recorded temperature on Uranus was - 224°C, which is the coldest temperature recorded on any of the planets.

Uranus has at least 27 moons, 13 rings and spins on its side like a ball rolling along its orbit. It is the only planet to do this.

A day on Uranus takes 17 hours, while a year is 84 times an Earth year.

is the eighth planet from the Sun and the second of the ice giants. It is the only planet in the Solar System that we cannot see with just our eyes.

It is about four times wider than Earth and thirty times further from the Sun.

At 4.5 billion km from the Sun, it receives very little heat and so has an average temperature of just -200°C.

Neptune has 13 moons. A day on Neptune lasts around 16 hours and it takes about 165 Earth years to orbit the Sun once.

Beyond Neptune is the .

Instead of rocky asteroids it contains objects made from ice, rock and dust, including the dwarf planet .

In terms of planets, dwarf planets and asteroids, this is the edge of the Solar System.

The gravitational force of the Sun reaches way beyond Pluto and the Kuiper Belt, to what is called the .

While planets and asteroids fly around the Sun in flat circular or oval orbits, the Oort Cloud is more like a sphere, with many icy objects spread out all around it.

No-one knows for sure, but it is thought that the closest part of the Oort Cloud might be 2, 000 times further from the Sun than Earth. Its furthest parts could be as far as 100, 000 times further away.

Comets

are frozen objects made from ice, dust and rocks. They sometimes come much closer to the Sun, which makes them warm up.

As they heat up, some of the ice melts. This releases glowing gases and dust which form a tail that stretches out behind the comet.

Some comets have regular orbits so astronomers can predict when they will be visible from Earth. Halley's comet was discovered in 1682 and returns every 76 years. It will appear next in the year 2062.

Our Sun seems much bigger than other stars in the sky because it is much closer to Earth. But compared to other stars it is only of average size.

Our Sun is just one of many billions of stars in our galaxy, which is called the Milky Way. The Milky Way is a spiral galaxy and our Solar System is about half-way along one of its arms.

Our Sun orbits the centre of the Milky Way at about 140 miles every second. It takes about 230 million years for for it, and us, to complete one full orbit.

And the Milk Way is just one galaxy in the Universe.

The Hubble Space Telescope has discovered around 100 billion galaxies and the James Webb Telescope will be able to find even more. Astronomers think that there are 200 billion or more galaxies.

The Universe is huge!

Solar System – A group of objects orbiting around a star.

Planet – A large, spherical object orbiting a star.

Moon – A large object orbiting a planet.

Orbit – the path an object takes round another object.

Day – the length of time a planet takes to complete one spin.

Year – the length of time a planet takes to complete one orbit of the Sun.

Mass – the ‘stuff’ that something is made of, all the matter that makes up that object.

Goldilocks Zone – the distance from a star where the temperature is not too cold, not too hot, but just right for the conditions for life to exist.