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The eight planets of the Solar System


Mercury is the closest planet to the Sun but surprisingly, not the hottest. It doesn't have an atmosphere so any heat the planet gets from the Sun quickly escapes back into space.

Temperatures can still get as high as 427°C which is 61 times hotter than the average temperature on Earth!

But because there is nothing to hold in the heat, Mercury can also reach temperatures as low as -173°C, almost twice as cold as the lowest temperature ever recorded on Earth.

No atmosphere also means the planet doesn't have a sky! If you could visit Mercury, you would be able to see stars at daytime and the Sun would look twice as big. Because Mercury is the closest planet to the Sun, it has a very quick orbit. This means it only takes 88 Earth days to go round the Sun which gives Mercury an 88-day year. But it rotates quite slowly and means that a day on Mercury lasts for 59 Earth days.

The first probe to reach Mercury was in 1974 and it mapped out the surface to find it was really similar to our moon with lots of craters.


Venus is the brightest object in our solar system after the Sun and our Moon which means on a clear night you might be able to see it without using a telescope. Because of this, people have known about its existence since prehistoric times and the first probe to visit it was in 1961.

Venus is sometimes called the 'Twin Planet' because it is similar to Earth. It's only slightly smaller than Earth and has an atmosphere complete with clouds.

These clouds are a bit more deadly than ours because they are made of sulphuric acid which is poisonous to us. Acid clouds, mixed with an atmosphere of carbon dioxide, make Venus the hottest planet in the solar system reaching 482°C – that's almost 7 times higher than the hottest
temperature ever recorded on Earth!

Venus also has the slowest rotation in the solar system meaning 1 day on Venus is the same as 243 days on Earth. But for Venus to orbit the Sun takes just 224 Earth days, which means that a year on Venus is shorter than a day!


Mars is also known as the 'Red Planet' because it has lots of iron oxide on its surface giving it that rusty red colour. It is the second-smallest planet in the system and fourth in line from the Sun meaning it can get pretty cold there.

Same as the Earth, it has a North and a South pole which are covered in ice, and reaching temperatures as low as -140°C. 20°C is the highest temperature on Mars, similar to a sunny day back here on Earth. A day on Mars is slightly longer than here at 25 hours, but a Mars year is almost twice as long as an Earth year, taking 687 days to orbit the Sun.

Mars also has the highest mountain in the solar system, called Olympus Mons, which measures around 15 miles high. That's three times taller than Mount Everest!


Earth is our home planet and the only one known to support life. It is the fifth- largest planet and is orbited by one moon. Our planet is the only one in the solar system to have water in its liquid form, which allows it to support life.

71% of Earth's surface is covered in water and the oceans help to keep the temperature cool enough for life to survive. It takes 24 hours for the Earth to rotate once – a day – and it takes 365 days for the Earth to orbit the Sun – a year.

The surface of our planet is very young because it is always changing. The surface is made up of different sections called tectonic plates which move over time, re-shaping the Earth's surface.
Even though the Earth is over 4 billion years old, it is expected to support life for another 500 million years.


Jupiter is the largest planet in the solar system and is 318 times bigger than the Earth! It's also the fastest rotating planet too, with 1 day only lasting 10 hours – but a year on Jupiter lasts for 12 Earth years.

Jupiter doesn't have a solid surface and is made up of gas, giving it the name 'gas giant'.

It has winds that can travel up to 400mph that swirl around the planet giving it bands and stripes. These coloured bands are called zones and belts. Each one has a slightly different
temperature and holds different chemicals to make them different colours.

Its most famous feature is its 'Red Spot', which is a storm that's so big it is visible from Earth. It's been raging for 300 years! Jupiter is the planet that has the most moons in the solar system. It has 4 main moons that were discovered by a famous astronomer called Galileo Galilei in 1610, but there are now thought to be up to 64 moons orbiting Jupiter.

Its biggest moon is called Ganymede, the largest moon in the solar system – which is
bigger than Mercury!


Saturn is the second biggest planet in our solar system. Similar to Jupiter it has over 60 moons and is made up of different gases. Even though it is a gas giant, it is also the lightest planet. Saturn is so light that it would float in water, if there was an ocean big enough.

Its most interesting feature is the series of rings that surround the planet. The rings aren't solid, but are made up of lots of little pieces of rock and ice particles that orbit Saturn at the same speed.

A day on Saturn is very short at only 11 Earth hours, but because it is so far from the Sun, 1 year is equal to almost 30 years on Earth! Saturn is also very cold because of its distance from the Sun, 25 times colder than the average temperature on Earth at -175°C.


Uranus is the third biggest planet in the solar system and the only planet that rotates on its side. Scientists think it may have been knocked over onto its side by another planet long ago.

This means that some parts of Uranus can't be reached by the Sun for long periods of time. Some nights can last as long as 40 Earth years there! Uranus was the first planet to be discovered by a telescope by Sir William Hershel in 1781.

Even though you could see it without a telescope, it hadn't been noticed before that time because it is quite dim and has a slow orbit.

The core of the planet is made up of ice and rock making it the coldest planet in the solar system with temperatures of -224°C, 32 times colder than the average on Earth! It also has a complex layer of clouds made of water and other chemicals. Scientists have even discovered that Uranus has its own weather activity and seasons. It has 27 moons and like Saturn, it also has a system of 11 rings orbiting it. They are very dim and difficult to see, but the brightest ring orbiting Uranus is called the Epsilon ring.


Neptune is the planet furthest away from the Sun and is made up of the same kinds of gases found on Uranus. Methane is the gas that makes up most of the atmosphere on Neptune and gives it that dark blue colour.

Because it was so far away with such a slow orbit, when Galileo observed Neptune in 1613, he thought it was a star. It was finally discovered by two different mathematicians in 1846.
Neptune is the windiest planet with winds that can reach up to 1,240mph, which
is three times faster than anything recorded on Earth.

It is 17 times bigger than Earth and takes 165 years to orbit the Sun. This means only one year on Neptune has passed since it was discovered in 1846 – happy birthday Neptune! It has 11 moons with a 16-hour day but even though it is the planet furthest away from the Sun, it is not the coldest, with temperatures of -218°C.


The Sun is at the centre of the Solar System, and its gravity holds all the planets in place.
The Sun is the biggest object in the Solar System and makes up 99% of its mass. Its diameter is around 109 times bigger than Earth, but you could fit over A MILLION Earths inside the Sun.
Astronomers think that the Sun

(and the planets) formed from the solar nebula about 4.59 billion years ago, so it's pretty old!

Its temperature is 5,500 degrees Celsius on the surface and a whopping 15.6 million degrees Celsius at the core. The temperature of the Sun isn't the same all over; in some places 'sun spots' occur where it isn't as hot than elsewhere.

It's made almost entirely of hydrogen, with a bit of helium and a few heavier gases including oxygen – and there's even some iron in there too. Light from the Sun reaches the Earth in just 8 minutes! Remember – don't ever look directly at the sun – you could seriously damage your eyes.

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