Ten things you didn't know about our Solar System

If you think you’re pretty clued up on the Solar System, think again.

Some of these facts are absolutely out of this world!

You can't stand on Uranus

An image of Uranus taken from the Voyager 2 in 1986 — Image caption,
Uranus’ clouds are made up of hydrogen sulphide, meaning they have a very similar smell to rotten eggs. Gross.

If we ever manage to travel to the gas planets, you might be in for a bit of a shock when you step off the spaceship. That’s because Jupiter, Saturn, Uranus and Neptune don’t have solid surfaces - they have a rocky core, but are mainly big balls of hydrogen and helium.

The whole of Mars is as cold as the South Pole

Meridium Planum, on the surface of Mars. — Image caption,
This is a photo of Meridium Planum, a plain on the surface of Mars.

If you’re travelling to Mars anytime soon, be sure to bring your big coat. Its average temperature is roughly -60°C, the same as the South Pole (minus the penguins). Some scientists, , have suggested ways in which we could make Mars warmer. One of these ideas is to build giant mirrors that will reflect the Sun's rays, and kick-start some speedy Martian warming.

Saturn's rings are 90% water

A monochrome photo of Saturn — Image caption,
If you like it then you should put a ring on it.

Saturn is home to the Solar System’s most epic ice rink. Being so far from the Sun, the water in its rings is frozen into ice. It is one of four planets that have rings around them - the other gas planets do too. However, the rest were undiscovered until the 1970s when probes went to explore them. Saturn’s were the first rings seen through telescopes from Earth.

Jupiter’s largest moon has a salty ocean that contains more water than on Earth

A photo of Jupiter and its largest moon Ganymede, taken from the Cassini spacecraft — Image caption,
Jupiter has 53 named and 14 unnamed moons. This is a photo of Jupiter and Ganymede.

Forget holidays in the Mediterranean. If you want vast ocean views, Jupiter’s biggest moon Ganymede is the place to be. The moon is larger than Mercury and would be classed as a planet if it were orbiting the Sun rather than Jupiter.

Mercury takes roughly three Earth months to orbit the Sun

An artist's impression of Mercury. — Image caption,
This is an artist's impression of Mercury. Mercury’s orbit is 88 days and it takes 59 days to rotate.

In three months you could write a book, pass your driving test or learn basic guitar. It’s also the amount of time it takes Mercury to travel around the Sun. It’s the shortest orbit in the Solar System, because Mercury is the closest planet to the Sun. So, next time someone asks you when you’ll get around to mowing the lawn, tell them it’ll be in roughly one Mercurian year.

It would take 100 times longer to travel around the Sun than the Earth

A photo of the sun — Image caption,
The sun accounts for 99.8% of the mass of the entire Solar System.

Long haul flights to the other side of the world can be gruelling, but it’s nothing compared to how long it would take to fly round the Sun. To go on this trip of a lifetime, you’d have to prepare yourself for a journey of 206 days. Let’s hope there are places to stop to refuel along the way.

A day is longer than a year on Venus

An artist's impression of Venus. — Image caption,
This is an artist's impression of Venus. Venus and Earth are very similar in size, but it is far less habitable - its surface temperature is 465°C, hot enough to melt lead.

This one might sound completely out there, but bear with us. A day is how long it takes a planet to rotate fully, and a year is how long it takes a planet to orbit the Sun. Venus is one of only two planets that rotates clockwise, and it spins much slower than others in the solar system. Some think this is due to it being knocked into a different direction by another planet, or it just gradually slowed to a halt then started turning the other way. It takes 243 Earth days for Venus to do one complete rotation, and 225 Earth days to orbit the Sun. Therefore, a day is longer than a year on Venus.

Pluto isn’t the only dwarf planet in our Solar System - we have six

An artist's impression of the five dwarf planets. — Image caption,
This is an artist's impression of five of the dwarf planets. Some of them have moons, too.

The first time you may have heard the term ‘dwarf planet’ was when Pluto got demoted to one in 2006 (RIP). However, we actually have six in our Solar System. Pluto, Ceres, Makemake, Haumea, and Eris were the only five that we knew about up until very recently. Ceres is in the asteroid belt between Mars and Jupiter, and became the first dwarf planet to be visited by a spacecraft in 2015. Recently though, a new dwarf planet has been discovered, which is officially called 2015 TG387, but has been given the nickname 'The Goblin'.

The Solar System is roughly 4.5 billion years old

A compilation of photos of the planets and the Earth's Moon — Image caption,
All the other planets in the solar system can fit inside Jupiter.

The Solar System is ancient. To put it into perspective, if the age of the Solar System were a year, humans would appear on Earth just before the countdown on New Year’s Eve.

The Solar System might not end with Pluto

An artist's impression of Tythe, in the Oort cloud. — Image caption,
This is an illustration of Tythe, a hypothetical planet three times as big as Jupiter that some scientists thought might be in the Oort cloud. NASA has since ruled that it doesn’t exist.

The Oort cloud is the Solar System's Terra Australis. It's a theoretical bubble of icy debris predicted by scientists to be the furthest part of our Solar System, but remains tantalisingly undiscovered. If the Earth was 1 centimetre away from the Sun, the Oort cloud would be half a kilometre away. Even so, there are parts of the distant Solar System that we know about, such as the Kuiper Belt.

This article was published in October 2018

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