Stars are born from big clouds of dust and gas - mostly hydrogen, helium and small amounts of heavier elements - which collapse due to gravity. Some of the gas and dust falling onto the star flattens out into a disc, like when a chef tosses a ball of pizza dough to flatten it into a pizza base. This disc of dust and gas around a baby star is where planets grow. You can think of the disc as a place where all the ingredients needed to make a planet are measured out and set up for you, and all that's left to have a solar system is make some planets!

In this disc, some places will be better for growing planets than others. Dust can sometimes get trapped in certain places, and you can end up with a big dust blob. In these dust blobs there is more dust than there is elsewhere, meaning there is a higher density of dust. Consider crossing a hall that only has a few people in it - it's easier to get through the room without bumping into anyone than it is to cross a crowded dance floor. This is because the dance floor has a higher density of people.

Places where there are higher densities of dust make it easier for planets grow by dust colliding and sticking together. This step can be tricky, because sometimes when dust and pebbles smash together, they break apart instead of sticking, but once the moment is right they'll stick and baby planets will grow. This process of the colliding and growing can continue all the way up until they are planet-sized, or some may stay smaller and end up being asteroids.

The baby planets we've made so far are rocky ones, like Mercury, Venus, Earth and Mars, but how do we get the giant planets like Jupiter, Saturn, Uranus and Neptune? If the rocky core we made by smashing dust together is big enough, it can gobble up gas and ice to get bigger, as long as it is far away from the star where it is cold.

If you stand right next to a campfire, it's warm, but as you move away, it gets colder - and the same is true for a star. To get more of the gases and ices onto your planet, you have to be further away from the star, where the ices survive. Then the baby planet can gobble up the gas and ice and sometimes may even act like an ice cream scoop and carve a gap into the disc around the star.

Planets grow from tiny pieces of dust to be the size of the Earth or even bigger in a few million years. It can be a messy process, but in the end, you have planets like our home, the Earth.