THE FORMATION OF THE SOLAR SYSTEM

Nobody knows for sure how the universe, its galaxies and their many millions of solar systems formed. We do have ways of looking back in time (in fact, every time we look at the Sun, we are looking eight minutes back in time!). This is because it takes light eight minutes to travel from the Sun to Earth. More distant stars may be hundreds of light years away, so when we look at them, we are seeing them as they were hundreds of years ago. However, we are not yet able to look back in time far enough to see how the universe actually began. But, we are able to watch the formation of other stars and know that, millions of years ago, the Sun began its life in a similar way.

Stars are born in swirlling clouds of dust and gas called nebulae. The tiny particles (called "matter") of this huge cloud combine with each other, forming a large star at the centre and planets surrounding it. It is believed that the Solar System, with its Sun, planets, moons, comets, asteroids and meteors formed in a similar way. To demonstrate the formation of a Solar System, join me and my dog, Bobsdog, in our Cosmic Kitchen.

COOKERY WITH BOB THE ALIEN

Right, here we are in our Cosmic Kitchen. Today, we're going to make a Solar System. This will only take a few billion years, but I'm sure the results will be worth the wait. Once we've done that, I'll tell you how to make Shepherds Pie.

Today's Recipe: A Solar System 
Tomorrow's Recipe: Shepherds Pie

Ingredients: Billions of billions of billions of tiny particles of dust, ice, rock, liquids and gases. These can be found anywhere, so there's no need to go searching around for years for them. In fact, you're probably surrounded by them right now without realising it!

Cooking time: Approximately 5 billion years
Best before date: Usually 10 billion years after start of mixture

COOKING INSTRUCTIONS

• STEP ONE
  Find an outer edge of a galaxy. Make sure you have plenty of space. About 5,000,000,000,000 kilometres wide should be just enough for an average-sized solar system. Spread the mixture of the ingredients (mentioned above) out evenly in this space. Call this mixture a nebula. The pull of the galactical centre of the galaxy should begin the process of stirring the particles in the nebula cloud. So, no need for a whisk! Below is what your mixture should look like by now.

• STEP TWO
  After a few million years, the moving particles of your nebula should start joining together with other moving particles. You will notice that most of the particles will join together with particles near the middle of the mixture. This is because the centre of the mixture has a strong gravitational pull, strengthened by the constant addition of little particles. The more particles in the centre, the stronger the gravtiational pull. Then, more particles are attracted. Below is what your Solar System should look like by now:

• STEP THREE
  Temperature of the mixture, especially at the centre, begins to increase as more particles get added to it. Eventually, mixture will get so hot at centre that the ball of particles will glow. This is the beginning of your new young star, which will be the centre point of your solar system. Cooking temperature at centre of this star will now be about 10,000,000 degrees celcius. Keep temperature about here and decrease after a while to create a star which could have nine planets orbiting it, maybe one of them with life. Decrease temperature immediately to prolong life of star, but cause it not to have enough heat to power a solar system properly. Or, increase temperature, creating a huge Blue Giant, shining blue, but causing it to have a shorter shelf-life (lasting only about one million years!).

• STEP FOUR
  While star is cooking at centre of solar system, monitor process of rest of solar system. Notice that your early nebula cloud is becoming less cloud-like and more separated into chunks. Notice how particles gather near the part between your star and the edge of the solar system, forming large balls of gas, although not large enough to be stars. Notice also that, between these and your new star, particles are gathering to form smaller, rockier worlds. You will name these objects planets. These planets all seem to spin round the star at the centre, with bigger clumps of dust smashing into them all the time.

• STEP FIVE
  As star brightens and gives off heat, cool down cooking temperature. This will cool down the temperature of the newly-formed planets, which have now begun orbiting the new star. These new planets are also now large enough to have strong gravitational pulls of their very own, causing smaller collections of particles to spin around them. These smaller collections of particles will be known as moons.

• STEP SIX
  After about 4 to 4.5 billion years, ensure that star is about average temperature. This means that it is causing temperatures at its nearest planet to be around 350°c and temperatures at its most distant planet to be around -230°c. Also ensure that all planets are spread out so that they have interesting individual features, so that people designing websites about them in the future can have something interesting to say about each one.

• STEP SEVEN
  After about 5 billion years, all planets should be settled in an orbit around the star, about half way through its age before it passes its best-before date. Some planets will still be forming, and so will some of their moons. Some may even have things living on them. It all depends on how the gases mixed together during the early cookery process.

By now, you should have your very own working Solar System. Eventually, the temperature of your star at the centre of it will burn up and swell into a red giant. This star will become so big that it may swallow some of the Inner Planets of your Solar System, but heat up any Outer Planets. Eventually, you'll run out of gas and the star will cool down, becoming a white dwarf, being smaller and cooler than it was once during its life time. As it cools further, it'll become a black dwarf or, if it was once a supergiant (a supernova), explode, fling out its gassy contents, and become an invisible pull of gravity, or Black Hole, sucking in the mass around it. This means that, once you've finished with your star, it'll vacuum up its own solar system, saving you the responsibility! Below is a picture of the explosion caused by a supernova (a star collapsing in on itself).