This morning's prompt was 'sidewinder'.

Looking at how planet agglomeration works in theory and in a sim named stargen. Planets sweep up dust and only accumulate gas if they're big enough and the medium is cold enough. Worrying about dust then gas, the sim places particles one by one to grab dust and maybe gas, with many 'duds' as the inventory is depleted. A particle has an orbit which it sweeps out between near and far based on eccentricity.