My point is that it would be a lot of effort for very little work to do it in the game itself, with an automatic calculation of the mass and density. The_Duck made a black hole plugin and if I remember right, they had their own gravitational fields. So, use a variation of that plugin, make a module named LargeBody or something, input gravitational parameters in the cfg, and you have yourself an asteroid you can land on. In fact, I might just do that myself.