There is nothing more marvellous than our solar system. It is the only place in the universe that is known (by us, at least) to support life, and part of the wondrousness of this strange little backwater in the Milky Way galaxy is its relative teeny-tininess.

Because, really, our galactic home is not hugely significant in the great scheme of things. Our planetary system is on one of the outer spurs of the Milky Way – a galaxy that has potentially four hundred billion stars and therefore four hundred billion potentially similar systems. Just to give you an idea, there are thought to be at least a hundred billion galaxies too.

Yet, enough of that; the numbers are too much for a mind to comprehend. Let’s focus on the thing that we know a bit more about – even if we don’t know much about it at all.

Because our solar system is full of amazing things – things that we’ve hardly begun to scratch the surface of. From balls of ice in the far reaches of the solar system to the gorgeous rings of Saturn, the system is really a quite amazing place.

Here, we’re going to run through some of the most important things that you should know about our neck of the galactic woods: how it was formed, what’s in it, and what lies beyond.  

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What is a Solar System? and How was it Formed?

The definition of a solar system is, if you think about it, really quite self-explanatory. It is made up of the sun and everything that orbits it gravitationally.

Just as Earth has a gravitational pull, so does every planet, star, or object in the universe. The bigger the object, the stronger the gravitational pull.

This is why the Sun – the biggest object in our solar system – is the thing around which everything spins. The planets – and all other sorts of things too – are all suspended by this solar pull, which allows us to refer to a thing called the solar system of things that all depend on each other.

But as we’ve said, it is wrong to call our solar system the solar system – as it is one of literally billions. The closest, by the way, is Proxima Centauri, some 4.2 light years away.

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So How was the Solar System Formed?

Like all solar systems, ours came into being through the collapse of an interstellar nebula or molecular cloud. These big drifting clouds of dust and gas slowly form into clumps due to the gravity of increasingly dense gases.

This all happened some 4.6 billion years ago, when the cloud core became the protostar which ultimately became the Sun. Meanwhile, as the gravitational pull of the Sun became stronger, the nebula would have started spinning more quickly, producing the accretion of ever larger planets and objects.

Quite an interesting thing to consider is that there would have been hundreds and thousands of protoplanets, dwarf planets, and general debris throughout the solar system, which either got destroyed over the years or else merged with other planets. The remnants of all this can still be seen in the asteroid belt beyond Mars and the Kuiper Belt beyond Neptune.

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planetary nebula - astronomy
Nebulae are some of the most beautiful things in the universe.

What’s in Our Solar System?

Now you know what a solar system is, let’s take a look in more detail at what you might find if you were to take a trip around it.

We suspect that you’ll find most of these names familiar already.

The Planets of Our Solar System.

There’s been a fair amount of discussion about the planets in our solar system in the last decade or so, as the definition of a planet was changed.

This meant that Pluto – poor Pluto – was kicked off the list and recognised instead as a dwarf planet.

So, what is a planet these days? It’s something incredibly specific actually, as such an object needs to meet four criteria:

  • It needs to orbit a star or the remnants of a star;
  • It should be big enough that its gravity has caused it to become round;
  • It should not be so big that it causes thermonuclear fusion – as a star would; and
  • It should have cleared its neighbourhood of celestial bodies, meaning that things either orbit it or do not exist anymore.

The Eight Planets in the Solar System.

  • Mercury – The closest planet to the Sun, it is also the smallest planet in the Solar System, with an orbit of around eighty-eight days. Like the Earth it is a rocky planet – and its surface is heavily cratered.
  • Venus – The second planet from the Sun, Venus is actually the brightest object in the night sky after the Moon – and it can actually cast a shadow. It is smaller than Earth and, like Mercury, does not have any moons.
  • Earth – Home sweet home. Earth is the third planet, and, like Venus and Mars, it sits in the Sun’s ‘habitable zone’. It is, however, the only planet to have an atmosphere that is actually habitable.
  • Mars – The Red Planet is the last of the terrestrial planets – those planets made of rock. We’ve done twenty-six successful missions to Mars with the hope that maybe we’ll find evidence of life.
  • Jupiter – Beyond the asteroid belt sits Jupiter, the largest of the solar system’s planets. It has a mass two and a half times that of all other planets combined. Made of gas, it has seventy-nine moons, some of which are bigger than Mercury.
  • Saturn – Famous for its rings – made of ice particles primarily – Saturn is the second-biggest planet in the solar system, and it too is a gas giant.
  • Uranus – Often used as a dirty pun, Uranus is the first of the ice giants – the two planets at the furthest end of the solar system. Predictably, it is made of ice.
  • Neptune – The final planet in the solar system, Neptune is cold – like, really cold.

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saturn and its rings
Saturn is one of the most beautiful planets. Image from NASA

The Solar System’s Dwarf Planets.

Beyond the major planets – which pretty everybody probably knows by heart – there are the dwarf planets. These are celestial bodies that aren’t quite planets, as they don’t fit the four criteria outlined above.

The most important of these criteria is that the dwarf planets have not ‘cleared their neighbourhood’ – meaning that they are not gravitationally dominant in their particular area.

Pluto, the most famous of the dwarf planets, has not cleared its neighbourhood, for example. Its orbit is affected by that of Neptune. Meanwhile, it moves in what is known as the Kuiper Belt, which, if it were a proper planet, would be in its gravitational sphere.

There are potentially hundreds of dwarf planets in the Solar System. However, identifying them requires a lot of work and observation. There are many candidates, but only five have been confirmed.

These are Pluto, Eris, Ceres, Makemake, and Haumea – of which only Ceres can be found in the asteroid belt between Mars and Jupiter. All the others are beyond Neptune.

What Else is in Our Solar System?

Whilst the most famous parts of the Solar System are those planets that are so well recognised, there are thousands of different bodies that constitute the rest of our solar system.

For example, there are thought to be over eight hundred thousand asteroids as well as three and a half thousand comets and over two hundred moons.

But think about it. The end of the solar system is thought to be where the solar wind reaches and where the sun’s gravity ends. And these are both huge distances beyond what we know of the solar system.

The limit of the solar wind is four times Pluto’s distance from the Sun, whilst the gravitational reach of the Sun stretches a thousand times further.

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space from the earth
The universe is just so incredibly - large.

And What’s Beyond Our Solar System?

When you look up at the night sky, the six brightest points of light you will see are all in the Solar System.

After that, however, the brightest things you will see are other stars at the centre of different solar systems.

The brightest of these are Sirius (or Canis Majoris), Canopus, and Rigil Kentaurus, part of the Alpha Centauri system (our star’s neighbour). These are all very close stars, with Sirius sitting in the Greater Dog constellation, Canopus in Carina, and Alpha Centauri in Centaurus.

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