> There's a catch: the volume formula is probably wrong because I've done it for a
> full sphere. How much of a "partial sphere" are we talking about? If it's half,
> divide the mass by 2.
>
> Also, we're talking about a hollow sphere, so I don't know how that affects the
> formulas. Maybe it doesn't because the impact may be reflected in the density
> formula.

It's not very easy, because you have to compute the partial surface area, and then use a nasty density integral, calculated on the mentioned partial spherical surface (and density happens not to be constant, which will bring major havoc inside the integral). Sadly I forgot all the formulas, maybe I could help if I had my books, but they are buried somewhere and it's 3AM...