I'm trying to auto-generate random solar systems, and I'm basically just allocating 2% of the total system mass to planets (and moons). It provides interesting results, I always have a few gas giants, I often have many Mars-and-Mercury-massed planets.
But to calculate surface gravity, I need a radius.
This largely depends on the planet's composition... which can be quite varied (and depends quite a bit on where it formed, how it formed, etc).
But if I have a planet with 0.7 Earth mass, and 35% of that is iron/nickel (or siderophile), and 50% lithophile, and so on, can a decent estimate of radius be determined?
Do I need the breakdown on composition to be per atomic element, or can this give decent ballpark numbers if I have the mass as the ratio of lithophile/siderophile/chalcophile/volatiles?
My understanding of physics in this arena is... inadequate. I do not believe it's enough to simply look up the density of these elements on Wikipedia and calculate backwards from volume. Certainly an iron core compresses a bit such that the density is quite higher than that of an iron ingot on the surface?