Density

Normal planet density in Stars! is approximately one planet for every 5000 l.y.^2. That is, if you divided the universe up into squares 70 l.y.^2. on each side, there would on average be one planet in each square.

Selecting Sparse decreases density to approximately one planet for every 6500 l.y.^2. Selecting Dense increases the density to approximately one planet for every 4000 l.y.^2. Choosing Packed increases the density in number of planets by 30% over Dense in all but the Huge universe (which is stuffed as full as is playable by the Dense setting).