Simple version
Planets form in the disc of gas and dust left around a young star. Tiny grains stick together. Those clumps collide and grow. Over time, some become planetesimals, then protoplanets, then full planets.
This process is called accretion. It is messy. Early solar systems are full of collisions, dust, heat and gravity.
Rock planets and gas giants
Close to the young Sun, it was too hot for lots of gas and ice to stay solid. Rocky material survived better, which helped make Mercury, Venus, Earth and Mars.
Farther out, colder regions allowed ice and gas to collect. Large cores could pull in huge atmospheres, forming gas giants like Jupiter and Saturn.
Common mistake
People often imagine planets forming neatly, like marbles being placed in order. It was not neat. It involved repeated impacts and unstable orbits.
The solar system we see now is the calmer result of a much more violent beginning.
Try it
Put small crumbs or grains on a plate and gently move the plate. Some pieces stick together. Others scatter.
This is not the same as gravity in space, but it helps show how small pieces can become bigger clumps over time.
AwareSTEM link
This page links gravity, chemistry, geology and astronomy. It also connects to exoplanets and the search for life.
What learners should notice
Planets are not separate from star formation. They are built from leftover material in a young star system.
This means the story of Earth begins before Earth existed, inside a disc of dust and gas around the young Sun.
Build the understanding
Use the sequence: dust grains, clumps, planetesimals, protoplanets, planets. Then add collisions, heating and sorting by distance from the Sun.
This helps explain why the inner planets are rocky and the outer planets became giants.
AwareSTEM activity idea
Use beads or different sized counters to model accretion. Small pieces gather into larger clumps. Then discuss what the model cannot show: gravity, heat and orbital motion.
Quick recap
How Planets Form sits inside the Earth Forms part of The Story of Everything. The main point is this: accretion, the disc, and why some became rock while some became gas.
By the end of this page, the learner should be able to explain the idea in plain English, connect it back to the timeline, and say why it matters beyond a school-style fact.
Key words to know
Use these as anchor words while learning this topic: How Planets Form, Earth Forms, evidence, time, change, system, signal, scale and connection.
The aim is not to memorise every word. The aim is to build a small vocabulary that helps the learner explain the idea clearly to someone else.
Question to ask
Ask: what does how planets form change in the bigger story?
A good answer should not stop at one fact. It should explain what came before, what changed, and how that change affected the next part of the timeline.