You're sort of conflating what scientists are pretty sure about in a general sense and what they actually know about how it works in the specifics. Take a look

You're sort of conflating what scientists are pretty sure about in a general sense and what they actually know about how it works in the specifics. Take a look at the wikipedia page for this topic: https://en.wikipedia.org/wiki/Nebular_hypothesis https://en.wikipedia.org/wiki/Nebular_hypothesis Just as an example: > The formation of planetesimals is the biggest unsolved problem in the nebular disk model. How 1 cm sized particles coalesce into 1 km planetesimals is a mystery. This mechanism appears to be the key to the question as to why some stars have planets, while others have nothing around them, not even dust belts.