Facts About Our Solar System

How old is the solar system?

Around 4.5 billion years young! It’s not the oldest or the youngest solar system we know of and it formed from densely packed clouds of dust and gas around 9 billion years after the Universe began.

It may seem crazy that we can estimate the age of our solar system, especially when you think the telescope was only invented 400 years ago. It’s worked out by studying meteorites (space rocks that fall to Earth) — some of these are believed to be as old as the solar system itself.
 

What are planets?

We might live on one, but not all planets are the same. Some (like the Earth) are rocky planets, which means that they’re made of rock and metals with a solid surface. They are the planets closest to the Sun in our solar system and are smaller and rotate more slowly than the ginormous gas giants.

There are no points for guessing that gas giants are made up mostly from gases (such as hydrogen and helium), but did you know they have a solid rocky core? I wouldn’t recommend visiting Jupiter’s core though — it’s even hotter than the surface of the Sun. Not much is known about the cores of gas giants because of their dense gassy atmospheres.

Test your class on their planet knowledge with this PowerPoint.
 

Which planet is closest to the sun?

Mercury is the closest planet to the Sun — in comparison, Earth is more than twice as far from the Sun. You might remember the mnemonic My Very Easy Method Just Speeds Up Naming Planets, which gives the order of the planets from the Sun: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, Pluto*.

(*Poor Pluto lost its status as a planet in 2006 for being too small. It’s still out there — sulking probably.)

Challenge your class to come up with a new mnemonic for remembering the order of the planets (excluding Pluto) with this poster activity.
 

Which planet is hottest?

That would be Venus. Despite not being the closest planet to the Sun, temperatures on the surface of Venus can reach over 450°C — hot enough to melt some metals. Venus’ hellish temperatures are a result of its super-thick atmosphere that’s made up mostly of carbon dioxide. Just like on Earth, this carbon dioxide acts as a greenhouse gas and traps heat from the Sun, warming the planet.
 

Which planet is the biggest?

It’s Jupiter, which has over twice as much mass as all the other planets in the solar system combined. It’s also the oldest planet in our solar system and is named after the king of the Roman gods (the equivalent of the Greek Zeus).

Being so humungous means Jupiter often takes the hit from comets and asteroids that might otherwise collide with Earth. It’s not all good news though: Jupiter can also alter the course of objects travelling through the solar system, potentially sending them our way, as the dinosaurs found out.
 

Which planet has the most moons?

Saturn clinches it over Jupiter by just a few moons, although not all of them are confirmed. A moon is a large object that orbits a planet, and these two planets are so colossal that their strong gravitational fields have been able to hold onto loads of moons.

Many of the moons in our solar system are really funky. Take Titan, for example. It’s a moon of Saturn with earthly features such as lakes and rivers. The difference is these lakes and rivers are formed of methane instead of water — so it’d be best to pack a nose peg if you’re ever headed there.
 

What is beyond the solar system?

Some say the solar system ends at Neptune, the furthest planet, but others say it’s where the Sun’s magnetic field ends (over 100 times further away from the Sun than the Earth is). Voyager 1, the most distant spacecraft ever to set off from Earth, is now past this point. But Voyager will take tens of thousands of years to get through the cloud of rocks and ice, known as the Oort Cloud, that surrounds the solar system.

There are over 100 billion stars in our galaxy (the Milky Way — anybody getting hungry?) and there are billions of other galaxies across the universe. That’s the potential for a heck of a lot of solar systems, each as interesting as our own.
 

Can you see planets with the naked eye?

It’s surprisingly easy (and satisfying) to see planets in our own solar system with the naked eye. Venus, Mars, Jupiter and Saturn often appear as bright stars in the morning or night sky. There are many helpful online guides and apps out there for working out the best time to take a look.

Why not set the coolest homework ever and challenge your class to spot a planet?