step 1: 5 billion years ago the sun formed from a cloud of gas and dust that collapsed because of gravity
step 2: after the cloud collapsed it formed into a rotating disk. very dense and hot in the center where the star began to form
step 3: the spinning motion of the disk caused it to flatten. planetesimals formed causing more changes to the disk
step 4: as the planetesimals grew their gravitational pull increased and the large planetesimals collected more of the gas and dust
step 5: small planetesimals collided with larger ones and the planets began to grow larger and more stable
step 6: each planet swept up the material in its region so the planetary orbits are separate from each other
