> Is it based simply on sampling a volume of observed space and extrapolating Yes, that's pretty much it. It's not as bad as perhaps it sounds. The age of t

> Is it based simply on sampling a volume of observed space and extrapolating Yes, that's pretty much it. It's not as bad as perhaps it sounds. The age of the solar system means that the asteroid belt is mostly stable, which means the distribution can be inferred. The Kuiper belt and Oort cloud may throw some outliers in occasionally, though. We don't know enough about them yet.