Exploring our solar system

Exploring our solar system

Photo by Mads Bødker - Creative Commons

Photo by Mads Bødker – Creative Commons

This month, our Principia Mission Space Diary investigates some of the things astronaut Tim Peake might see in space, like the planets in our solar system.

All the planets orbiting our sun are unique. They have different landscapes, atmospheres and rotation speeds. To help our young Space Apprentices explore the planets without having to leave Earth, we’ve put together some information for them.


A huge thank you to Year 11 student Anna Fleming, from St George’s School for Girls in Edinburgh, who’s written a fabulous piece for us about Mercury. Thank you Anna for leading our expedition into outer space!


by Anna Fleming

Daytime temperatures on Mercury can reach 800 degrees Celsius. This is because the sun is 38.98 miles from Mercury. Compare this distance to Earth’s distance from the sun – 91.4 to 94.51 million miles – and you can see just how exposed Mercury is to the sun’s heat.

The scorching heat of the day is followed by freezing nights – Mercury is a planet of two extremes. Night time temperatures can go down to minus 290 degrees, as cold as deep space. At this temperature, you would freeze to death instantly. It gets so cold because Mercury does not have an atmosphere to trap heat and regulate temperature. Due to these extremes in temperature, it is impossible for water to exist on Mercury.

During the day and the night, the sky over Mercury is black, also due to the lack of an atmosphere to scatter the sun’s light. Its surface is similar in appearance to our moon, with craters from meteorite impact dotted around and regions of smooth plains. Most of the craters were a result of Mercury being heavily bombarded with meteorites 4.6 billion years ago. These craters can span hundreds of kilometres across and 2 kilometres deep – better watch your step!

There is no weather system on Mercury due to the lack of atmosphere, meaning you wouldn’t have to worry about any storms or hurricanes. However, there are the extremes in temperatures and the occasional earthquake due to compression forces ‘shrinking’ the planet.

The gravity on Mercury is only 38% strong as the Earth’s. This means you could jump three times as high and would be able to easily pick up really heavy objects. Playing football in these gravity conditions would be difficult. The ball would stay in the air for a long time and would go huge distances even with a gentle kick. You would need a much larger pitch and be prepared to use big leaps and jumps to get the ball.


Venus is the hottest planet in our solar system. Its surface can reach temperatures of up to 480 degrees Celsius. This is because it has a permanent layer of thick clouds, which trap in the heat and cause a greenhouse effect. The heat has boiled all the water out of Venus’ atmosphere, which means its surface is too hostile to sustain life.

Venus is not a very welcoming planet. Beneath its clouds of sulfuric acid droplets is a landscape of volcanoes, mountains and craters. Temperatures during the day and night are similar, because of the solar winds which move slowly across Venus’ surface. These winds aren’t like a refreshing breeze though – they only make Venus hotter.

Even though scientists think Venus might once have been a lot like Earth, possibly even with oceans, it has no moon or any seasons. The reason there are no seasons is because Venus doesn’t tilt on an axis, the way Earth does.

The days on Venus are very, very long because Venus spins so slowly. It takes 243 Earth days to equal one day on Venus. Imagine how long that would make your school day! Venus also spins in the opposite direction to the other planets in our solar system, with the sun rising in the west and setting in the east. This may have been caused by an asteroid colliding with Venus and changing its rotation.

The days on Venus might be long, but the years are short – shorter than the days in fact! It takes only 225 Earth days for Venus to orbit the sun, making its year shorter than its day. If you are 10 on Earth, you would be 16 on Venus, but you would only have been alive for 15 Venus days. There’d be days on Venus when you’d have to have more than one birthday!

Despite its harsh landscape and strange rotation, Venus is the brightest natural object in the sky, after the moon and the sun, of course. Because it’s so bright, lots of ancient civilisations had myths about it. This may also be the reason that it was named after the Roman goddess of love and beauty – quite a contrast to its barren and hostile landscape!


Our home planet is the only planet in our solar system known (at present!) to support life. Everything Earth’s inhabitants need to stay alive exists under the thin layer of Earth’s atmosphere, which divides our world from outer space.

Earth is a solid planet whose surface is covered in diverse terrain: mountains, forests, valleys, plains, polar caps and deserts. But one of the key differences between Earth and the other planets in our solar system is water. Around 70% of the Earth’s surface is covered in oceans, and we have rivers, lakes and other bodies of water on top of this. Earth’s water was originally trapped within the planet, but over time volcanic action brought this water to its surface.

Earth has an ozone layer, made from a special kind of oxygen. Like a protective shield around the planet, the ozone layer absorbs most of the sun’s harmful UV rays. This is why preserving our ozone layer is so important – we don’t want to let those nasty rays into our home!

Did you know that your compass wouldn’t work the same way on other planets? Earth has a powerful magnetic field, which we’ve been using for centuries to help us find our way. Scientists believe that it exists because of Earth’s rapid rotation on its axis, and its nickel-iron core. But our magnetic field isn’t just a useful navigation tool. It protects Earth from the effects of solar winds. Solar winds are charged particles that flow from the sun. They can travel at up to 900 kilometres per hour, and reach temperatures of one million degrees – Earth would be very different without our protective magnetic field!


Mars has fascinated Earthlings for a long time, and not just because of its unusual red glow. Scientists believe intelligent life once lived on Mars, which led to the theory of Martians. This is partly because Mars is similar to Earth in many ways. It has seasons like earth, even though these last twice as long and are more extreme than we’re used to, and is the only other planet with polar caps.

Ice water has been found beneath the Martian polar caps, and there’s also evidence of water in the icy soil and thin clouds. The atmosphere is too thick for water to exist as a liquid on the surface of Mars, but the terrain suggests that there were floods long ago. Because of the presence of water, scientists are researching whether it might be possible for people to live on Mars one day.

Like Earth, Mars has volcanoes and canyons. One vast canyon system runs along Mars’ equator and is as long as the United States. And we think the Grand Canyon is big! Mars has our solar system’s highest mountain, which is called Olympus Mons. This mountain is a volcano 21 kilometres high and 600 kilometres wide. Mount Everest is 8.8 kilometres high. Can you imagine something nearly three times higher? Scientists have found evidence of lava on Olympus Mons, which means it’s still an active volcano. It’d be exciting to see it erupt from the ISS!

Even though Mars has some similarities to Earth, there are lots of differences too. Instead of one moon, Mars has two. They’re called Phobos and Deimos. They are much smaller than our moon, aren’t smooth and round, and orbit quite close to the Martian surface. Mars has gravity like Earth, but it’s only 38% as strong. This means that you could jump more than three times as high on Mars.

The days on Mars are only a little bit longer than on Earth – 24.617 hours – but one year takes 687 Earth days. This is because of Mars’ big and elliptical orbit, which gives Mars six seasons instead of four. These extra two seasons are called perihelion, when Mars is closest to the sun, and aphelion, when it’s furthest from the sun. The elliptical shape of Mars’ orbit also creates the largest and fiercest dust storms in our solar system. These can last for months and cover the whole planet. It wouldn’t be much fun living on Mars during one of these storms!


Jupiter is the biggest planet in our solar system, which is why it was named after the Roman god of gods, and the god of the sky. Jupiter is so massive that it would take eleven Earths lined up side-by-side to equal the distance from one side of Jupiter to the other, and 317 Earths to equal its mass.

Unlike Earth, Jupiter doesn’t have a solid surface. It’s one giant ball of gas. This means there’s nowhere for a spacecraft to land. Jupiter has a unique cloud layer in its upper atmosphere, which gives it its unusual marbled appearance. Its cloud belts are made of ammonia crystals and sulfur – imagine how that would smell! Jupiter also has three rings: two faint outer rings and one thick inner ring.

Jupiter has 67 moons in total, all orbiting around it. Its moon called Ganymede is the biggest moon in our solar system. All these moons whizzing around Jupiter make it a bit like a solar system. Scientist believe that if Jupiter was just 80 times bigger, it would have turned into a star, like our sun.

Jupiter wouldn’t be a very nice place to visit, even if there was somewhere to land. Its pressure is so intense that anything that gets through its clouds is crushed and melted. It also has a giant storm called the Great Red Spot. This storm is bigger than Earth and has been raging for hundreds of years!

If you lived on Jupiter, you’d have a very short day at work or school because your whole day and night would be just under ten Earth hours long. Even though your day would be short, your year would last nearly 12 Earth years, so you’d have to wait a long time for your birthday. You’d have plenty of time to plan your party though!


Saturn is famous for its seven rings, which often make it people’s favourite planet. These beautiful rings have puzzled scientists since they were discovered by Galileo in 1610. The ring system is made from billions of particles, which can be tiny icy grains or as large as mountains. The reason we can see the rings from Earth with a telescope is because they’re made from ice. If you’ve seen a frozen lake on a sunny winter’s day, you’ll know that ice is very reflective. Just like the planets moving around the sun, each ring orbits around Saturn at its own speed.

Like Jupiter, Saturn is a gas giant, made from hydrogen and helium, the same gas we use to fill up balloons. Saturn is the least dense planet in our solar system. Because it’s mainly made of hydrogen, it’s less dense than water. This means it could theoretically float if you found a bathtub big enough to put it in.

Saturn has 150 moons and some smaller ‘moonlets’. Each moon is frozen like an ice cube. Saturn’s moons all have interesting and unique qualities, which scientists are still discovering. The moon called Enceladus appears to have an ocean hidden below its frozen surface. Another moon, called Titus, looks like it may have life on it, but its frozen surface of liquid methane lakes and landscape of frozen nitrogen would mean life would be very different to the kind we know on Earth. Another moon called Pan orbits within the main rings of Saturn, sweeping materials out of a narrow space called the Encke Gap.

Saturn has an unusual hexagon shape which surrounds its north pole. The hexagon is a six-sided jet stream which rotates. It is so big that it spans 30,000 kilometres – more than twice the diameter of Earth! The discovery of this strange phenomena thirty years ago helped scientists calculate the rotation speed of Saturn, which is 10.7 Earth hours.

Even though you can’t see Saturn’s rings without a telescope, you can still see the planet from Earth. It’s a pale yellow colour because its upper atmosphere contains ammonia crystals. On Earth, we often use ammonia in cleaning products, especially for glass and stainless steel. Do you think this would make Saturn sparkling and clean?


Uranus is a cold and windy planet made of gas. It was the first planet to be discovered by telescope, which means you can’t see it from Earth with the naked eye. If you get a chance to look at Uranus, you’ll see it’s a pale blue colour. This is because its upper atmosphere is made from water, ammonia and methane ice crystals.

Since its discovery in 1781, scientists have learnt all kinds of interesting things about Uranus, like its strange tilt. Its equator is nearly at right angles with its orbit, meaning that it spins on its side. Instead of moving like a spinning top around the sun like the other planets, Uranus looks like it rolls around the sun. Because of this, scientists have given it the nickname ‘the sideways planet’. Their theory is that something the size of Earth collided with Uranus, dramatically changing the angle it rotates at.

Like Earth, Uranus has seasons, but these are very different from the seasons we know. Each season on Uranus lasts 42 years! One hemisphere of the planet will have non-stop daylight and heat, when it faces the sun. During this time, the other half of the planet has a long, dark winter. The planet slowly rotates so that the other hemisphere is facing the sun, and the seasons reverse. You’d have a very long summer holiday if you went to school on Uranus!

Even though Uranus has such a long summer, it’s the coldest planet in our solar system because it’s so far away from the sun. Uranus is called an ‘ice giant’ planet, because it has an icy mantle which surrounds its rock and iron core. Its minimum surface temperature is minus 224 degrees Celsius – you wouldn’t need a fridge!

Uranus has 13 rings, but they’re not spectacular like Saturn’s. Uranus’ strange tilt means its rings are perpendicular to the sun. Scientists think the rings are made from pieces of comets and moons that collided and broke apart. The dust and debris caused in these collisions is the reason why Uranus’ rings aren’t as beautiful as Saturn’s icy ones. Some researchers believe these rings are still very young, so who knows how they might change over the next few centuries!


Earthlings didn’t know Neptune existed until 1846 because it is so far away from our home planet. It takes such a long time for Neptune to move around the sun – 165 Earth years – that it has only completed its orbit once since humans discovered it. Even though its year is so long, a day on Neptune only takes 16 Earth hours. This is because it spins very quickly on its axis.

Neptune is cold, dark and very, very windy. Its supersonic winds are three times stronger than those on Jupiter and nine times stronger than Earth’s winds. Not very good weather for flying kites!

Are you afraid of storms? Then Neptune isn’t the place for you. Neptune’s biggest storm is called the Great Dark Spot, which is about the same size as Earth. The longest storm on record started in 1989 and lasted five years! Neptune has a second, smaller storm which is about the size of Earth’s moon and is called the Small Dark Spot.

Neptune is an ice giant like Uranus. It’s made from a combination of water, ammonia and methane. The layer of methane gas above its clouds gives Neptune its blue colour, which is why it was named after the Roman God of the Sea. Methane absorbs red light, which is why this planet looks so blue.

There are fourteen known moons orbiting Neptune. The largest moon – Titan – is one of the coldest worlds in our solar system. It spits out particles of nitrogen ice and dust from its surface – not very welcoming for space explorers!

Like Uranus, Neptune also has six faint rings. These are made from ice particles and grains of dust coated in a carbon-based substance. Scientists believe these rings are very young, and won’t last for a long time, so Saturn doesn’t have to worry about being outdone!

Congratulations on completing your mission to explore our solar system. Have a safe journey back to planet Earth, Space Apprentices!