A "planetary system" is any group of planets that orbits a star that all those planets share....
The name of our star ( called the sun ) is "Sol" so if we live on any planet that Orbits the star called "Sol" we are living in the "Sol-ar" system....Okay?

So, where did all the planets come from?
Gigantic clouds of gas and dust float around in space, Most of this gas and dust comes from old stars that have died and exploded in a Supernova Explosion, or, maybe just a star has fizzled out and the leftover has drifted off into space...
These clouds are called Nebula (Latin for cloud), everything in space makes its own gravity, so like magnets the dust and gas starts to "fall" together....

The in-falling gas and dust starts to form a gigantic whirlpool in space, with most of the gas and dust (we will call "star stuff"), collects more and more in the middle of the swirling cloud.
This can go on for millions of years and as the middle of the whirlpool gets more and more star stuff, things start to heat up..... a lot!
Soon a big ball of star stuff has formed at the centre, the bigger it is the hotter it gets and the more pressure there is.
At some point, an element called Hydrogen, gets so hot and the pressure so great, that it starts to from a different gas called Helium, the process is known as "fusion".

It is at that point that the ball becomes a new Star!

Meanwhile....elsewhere in the swirling cloud......
In the same whirlpool, there might be big lumps of dust and even rocks! These also have gravity and start to form their own littler whirlpools in the arms of the bigger one.
These start to "lump" together to form bigger and bigger lumps, the bigger they get, more gravity they have and the more hungry they get! soon they pull in all the remaining dust and rocks and gases that are near them.
As this is happening these growing lumps are "Orbiting" (going around and around) the star that is at the middle of the BIG whirlpool.
These lumps start to get so big that star stuff, is pulled into them with crashing speed, this melts the star stuff when it hits.... we get a big melted ball of melted (Molten) rock.....
We call it a Planet.

What about our new star (Sun)?
By now the new star has turned on and the heat and gas it is giving off, makes a kind of wind called the "Solar wind".
This "wind" pushes the lighter than rock gas out and away from the new star. Then just like the rocky planets before, these gasses start to form their own smaller whirlpools, as this gas "obits the new star...

The gasses form big balls of gas and any left over dust that the rocky planets missed, and all this happens so far out from the star at the centre that the gas cools down and down, until it turns to liquid (all gas turns to liquid form if you get it cold enough).
We now have a different type of planet in orbit around our new star... A "GAS" Planet. Normally they are huge, Jupiter is a gas planet, a type called "a gas giant".

Jupiter, Saturn, Neptune and Uranus are gas giants, they are the outer planets of our "Solar" system. Towards the middle we find rocky planets, Mars, Earth, Venus, and Mercury.
We notice that as we get closer to the sun the star stuff that makes up the planets is heavier (More dense) the lighter star stuff got pushed away from the new star when it turned on.... also the heavier stuff got pulled in closer to the growing star right at the start......

If you look at the Rings of Saturn, you can see leftover star stuff drifting around this planet, also most of the moons of the planets are star stuff left overs....

What about Pluto?
The Ninth planet out from our star (the sun or Sol) is a small rocky world called Pluto.
Its an odd ball because its rocky and it's orbit is a bit like a buckled wheel on a bike. Pluto's orbit is also, very "elongated" (shaped like a football) a stretched out oval. Its' Orbit is tilted and stretched..... It seems that, Pluto was wandering past our new Solar system and got grabbed by the gravity of the new Star and all the planets.

These days, planets are still growing! even today....
When ever you look up into the night sky and see a "shooting star", you are seeing the process of planet formation still in progress!!!
Shooting stars are tiny specks of dust like a grain of sand, that are still floating around the solar system. More left overs...
Bigger shooting stars, light up the night sky! We call them "Fire balls" and they can be from the size of a golf ball to a car!
These Shooting stars are called "Meteors" and if they reach the ground, "Meteorites".....They light up because they are going SO FAST that the Air rubbing on them makes them "white hot" and they melt away as they fall through the air. Only the bigger ones (about the size of a 20 cent piece) or more solid ones, make the fiery trip through the Atmosphere and hit the ground.

The really Big ones will blast a "Crater" in the ground!
Every day over 300 tones of shooting stars fall into out planet! So Earth "grows" by 300 tones a Day!!!!

Cool huh?

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